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  • 1.
    Aghaali, Habib
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Ångström, Hans-Erik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    A review of turbocompounding as a waste heat recovery system for internal combustion engines2015In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 49, p. 813-824Article in journal (Refereed)
    Abstract [en]

    Internal combustion engines waste a large amount of fuel energy through their exhausts. Various technologies have been developed for waste heat recovery such as turbocompounds, Rankine bottoming cycles, and thermoelectric generators that reduce fuel consumption and CO2 emissions. Turbocompounding is still not widely applied to vehicular use despite the improved fuel economy, lower cost, volume, and complexity higher exhaust gas recirculation driving capability and improved transient response. This paper comprehensively reviews the latest developments and research on turbocompounding to discover important variables and provide insights into the implementation of a high-efficiency turbocompound engine. Attention should be paid to the optimization of turbocompound engines and their configurations because the major drawback of this technology is additional exhaust back-pressure, which leads to higher pumping loss in the engines. Applying different technologies and concepts on turbocompound engines makes the exhaust energy recovery more efficient and provides more freedom in the design and optimization of the engines. Turbine efficiency plays an important role in the recovery of the wasted heat so turbine design is a crucial issue in turbocompounding. In addition, variability in geometry and rotational speed of power turbines allows for more efficient turbocompound engines in different operating conditions. The conclusion drawn from this review is that turbocompounding is a promising technology for reducing fuel consumption in the coming decades in both light- and heavy-duty engines.

  • 2.
    Aghaali, Habib
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Ångström, Hans-Erik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    The Exhaust Energy Utilization of a Turbocompound Engine Combined with Divided Exhaust Period2014Conference paper (Refereed)
    Abstract [en]

    To decrease the influence of the increased exhaust pressure of a turbocompound engine, a new architecture is developed by combining the turbocompound engine with divided exhaust period (DEP). The aim of this study is to utilize the earlier stage (blowdown) of the exhaust stroke in the turbine(s) and let the later stage (scavenging) of the exhaust stroke bypass the turbine(s). To decouple the blowdown phase from the scavenging phase, the exhaust flow is divided between two different exhaust manifolds with different valve timing. A variable valve train system is assumed to enable optimization at different load points. The fuel-saving potential of this architecture have been theoretically investigated by examining different parameters such as turbine flow capacity, blowdown valve timing and scavenging valve timing. Many combinations of these parameters are considered in the optimization of the engine for different engine loads and speeds.

    This architecture produces less negative pumping work for the same engine load point due to lower exhaust back pressure; however, the exhaust mass flow into the turbine(s) is decreased. Therefore, there is a compromise between the turbine energy recovery and the pumping work. According to this study, this combination shows fuel-saving potential in low engine speeds and limitations at high engine speeds. This is mainly due to the choked flow in the exhaust valves because this approach is using only one of the two exhaust valves at a time. To reveal the full potential of this approach, increasing the effective flow area of the valves should be studied.

  • 3.
    Aghaali, Habib
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Ångström, Hans-Erik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Serrano, Jose R
    Universitat Politècnica de València.
    Evaluation of different heat transfer conditions on an automotive turbocharger2014In: International Journal of Engine Research, ISSN 1468-0874, E-ISSN 2041-3149, Vol. 16, no 2, p. 137-151Article in journal (Refereed)
    Abstract [en]

    This paper presents a combination of theoretical and experimental investigations for determining the main heat fluxes within a turbocharger. These investigations consider several engine speeds and loads as well as different methods of conduction, convection, and radiation heat transfer on the turbocharger. A one-dimensional heat transfer model of the turbocharger has been developed in combination with simulation of a turbocharged engine that includes the heat transfer of the turbocharger. Both the heat transfer model and the simulation were validated against experimental measurements. Various methods were compared for calculating heat transfer from the external surfaces of the turbocharger, and one new method was suggested.

    The effects of different heat transfer conditions were studied on the heat fluxes of the turbocharger using experimental techniques. The different heat transfer conditions on the turbocharger created dissimilar temperature gradients across the turbocharger. The results show that changing the convection heat transfer condition around the turbocharger affects the heat fluxes more noticeably than changing the radiation and conduction heat transfer conditions. Moreover, the internal heat transfers from the turbine to the bearing housing and from the bearing housing to the compressor are significant, but there is an order of magnitude difference between these heat transfer rates.

  • 4.
    Alenius, Emma
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Sound Generating Flow Structures in a Thick Orifice Plate Jet2014In: Progress in Turbulence V: Proceedings of the iTi Conference in Turbulence 2012, Cham, Switzerland: Springer, 2014, p. 201-204Conference paper (Refereed)
    Abstract [en]

    The aim of thiswork is to study sound generating flowstructures in a thickcircular orifice plate jet, placed in a circular duct. Large eddy simulations (LES)are performed for two jet Mach numbers, 0.4 and 0.9. Characteristic frequenciesin the flow, and their corresponding flow structures, are identified with dynamicmode decomposition (DMD). The results show that a tonal noise is generated atfrequencies where the jet displays strong ring vortices, in the plane wave range.The main sound generating mechanisms seems to be a fluctuating mass flow at theorifice opening and a fluctuating surface force at the plate sides, caused by the ringvortices. The frequencies are believed to be chosen, and strengthened, by a feedbackmechanism between the orifice in- and outlet.

  • 5.
    Alenius, Emma
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Large eddy simulations of acoustic-flow interaction at an orifice plate2015In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 345, p. 162-177Article in journal (Refereed)
    Abstract [en]

    The scattering of plane waves by an orifice plate with a strong bias flow, placed in a circular or square duct, is studied through large eddy simulations and dynamic mode decomposition. The acoustic-flow interaction is illustrated, showing that incoming sound waves at a Strouhal number of 0.43 trigger a strong axisymmetric flow structure in the orifice in the square duct, and interact with a self-sustained axisymmetric oscillation in the circular duct orifice. These structures then generate a strong sound, increasing the acoustic energy at the frequency of the incoming wave. The structure triggered in the square duct is weaker than that present in the circular duct, but stronger than structures triggered by waves at other frequencies. Comparing the scattering matrix with measurements, there is a good agreement. However, the results are found to be sensitive to the inflow, where the self-sustained oscillation in the circular duct simulation is an artefact of an axisymmetric, undisturbed inflow. This illustrates a problem with using an undisturbed inflow for studying vortex-sound effects, and can be of interest when considering musical instruments, where the aim is to get maximum amplification of specific tones. Further, it illustrates that at the frequency where an amplification of acoustic energy is found for the orifice plate, the flow has a natural instability, which is suppressed by non-axisymmetry and incoming disturbances.

  • 6.
    Alenius, Emma
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    LES of Acoustic-Flow Interaction at an Orifice Plate2012In: 18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference), 2012Conference paper (Other academic)
    Abstract [en]

    The scattering of plane waves by a thick orifice plate, placed in a circular or square duct with flow, is studied through Large Eddy Simulation. The scattering matrix is computed and compared to measurements, showing reasonably good agreement except around one frequency ($St \approx 0.4$). Here a stronger amplification of acoustic energy is observed in the circular duct simulations than in the measurements and the square duct simulations. In order to improve the understanding of the interaction between an incoming wave, the flow, and the plate, a few frequencies are studied in more detail. A Dynamic Mode Decomposition is performed to identify flow structures at significant frequencies. This shows that the amplification of acoustic energy occurs at the frequency where the jet in the circular duct has an axisymmetric instability. Furthermore, the incoming wave slightly amplifies this instability, and suppresses background flow fluctuations.

  • 7.
    Alenius, Emma
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Scattering of Plane Waves by a Constriction2011In: Proceedings of ASME Turbo Expo 2011, Vol 7, Parts A-C, American Society Of Mechanical Engineers , 2011, p. 1043-1052Conference paper (Refereed)
    Abstract [en]

    Liner scattering of low frequency waves by an orifice plate has been studied using Large Eddy Simulation and an acoustic two-port model. The results have been compared to measurements with good agreement for waves coming from the downstream side. For waves coming from the upstream side the reflection is over-predicted, indicating that not enough of the acoustic energy is converted to vorticity at the upstream edge of the plate. Furthermore, the sensitivity to the amplitude of the acoustic waves has been studied, showing difficulties to simultaneously keep the amplitude low enough for linearity and high enough to suppress flow noise with the relatively short times series available in LES.

  • 8.
    Allam, S.
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Cooling fan noise control using micro-perforates2012In: Int. Congr. Expos. Noise Control Eng., INTER-NOISE, 2012, p. 10434-10445Conference paper (Refereed)
    Abstract [en]

    Baffle or split silencers are commonly used, e.g., in HVAC systems and as inlet/outlet silencers on gas turbines. Another application is to reduce noise from the cooling fan inlet for large IC-engines. A baffle silencer can be seen as a periodic arrangement of parallel rectangular absorbers which can be placed in a rectangular duct. The noise reduction afforded by parallel baffles depends not only on the physical properties of the lining, but also upon the angle of incidence of the sound waves impinging and the baffle length. In this paper the potential of using baffles made of Micro-Perforated Panels is investigated in particular with the cooling fan inlet application in mind. Theoretical models for the damping is derived and used to design optimum configurations. The models are based on the wave propagation in a periodic array of baffles so that only one period can be investigated in order to find the different modes. In particular the least attenuated mode is important to find in order to optimize the behavior. An important aspect is the inner structure of the MPP baffle, i.e., can it just be an empty air volume or to what extent must internal waves be prevented by putting in walls. From a stiffness point of view some inner walls might also be needed to avoid vibration problems. Due to these complexities the theoretical models are only presented for the simplest cases. In order to validate the models and to get a more complete test of different designs experiments were also carried out. During these experiments the effect of flow was also tested.

  • 9. Allam, S.
    et al.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Investigation of aerodynamic installation effects for an axial fan2013In: 19th AIAA/CEAS Aeroacoustics Conference, 2013Conference paper (Refereed)
    Abstract [en]

    The aim of the work reported in this paper is to investigate the aerodynamic installation effects for a generic cooling fan system. This is done by treating the ducted fan as a multi-port source and performing a source characterization, i.e., determining the source strength and source reflection matrix. From the source strength, which represents the sound radiated by the fan in a reflexion free (infinite) duct, the effect of various inflow distortions can be studied. The work is part of the EU-project ECOQUEST where the data will be used to validate the acoustic prediction tools.

  • 10.
    Allam, Sabry
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Knutsson, M.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Development of acoustic models for high frequency resonators for turbocharged IC-engines2012In: SAE Technical Paper 2012-01-1559, 2012, 2012Conference paper (Refereed)
    Abstract [en]

    Automotive turbo compressors generate high frequency noise in the air intake system. This sound generation is of importance for the perceived sound quality of luxury cars and may need to be controlled by the use of silencers. The silencers usually contain resonators with slits, perforates and cavities. The purpose of the present work is to develop acoustic models for these resonators where relevant effects such as the effect of a realistic mean flow on losses and 3D effects are considered. An experimental campaign has been performed where the two-port matrices and transmission loss of sample resonators have been measured without flow and for two different mean flow speeds. Models for two resonators have been developed using 1D linear acoustic theory and a FEM code (COMSOL Multi-physics). For some resonators a separate linear 1D Matlab code has also been developed. Different models, from the literature, for including the effect of mean flow on the acoustic losses at slits and perforates have been implemented in the codes and compared to the experimental data. Correct modeling of acoustic losses for resonators with complicated geometry is important for the simulation and development of new and improved silencers, and the present work contributes to this understanding. The developed models give acceptable agreement with the measured results even with flow but can be improved for 3D FEM if correct CAD data is available. The 1D linear theory can be used for simple geometries and to get a general overview related to the resonance frequencies and damping level.

  • 11.
    Allam, Sabry
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Acoustic modelling and characterization of plate heat exchangers2012In: SAE Technical Paper 2012-01-1562, Society of Automotive Engineers, 2012Conference paper (Refereed)
    Abstract [en]

    There is increased concern about the noise emission from cooling systems. This is mainly due to an increased need for cooling needs due to turbo-charging and EGR systems, which tend to increase the fan power and thereby the noise. An important issue in this context is the behavior of the heat-exchanger and its acoustic transmission and absorption properties. In this paper an acoustic model to evaluate such data for a common type of heat exchanger, the parallel plate type, is presented. The basic configuration is assumed to be a matrix of parallel, narrow channels. The developed model is based on a so called equivalent fluid for an anisotropic medium. It is mainly dependent on the heat exchanger geometry combined with the Kirchhoff model for thermo-viscous wave propagation in narrow tubes. The proposed model can be used to predict the sound transmission and absorption for an entire heat exchanger for incident plane waves. This model is validated by comparison with measurement results for seven different heat exchangers used in vehicle and train cooling units at different flow speeds

  • 12.
    Allam, Sabry
    et al.
    Helwan University, Cairo, Egypt.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Fan Noise Control Using Microperforated Splitter Silencers2014In: Journal of Vibration and Acoustics-Transactions of the ASME, ISSN 1048-9002, E-ISSN 1528-8927, Vol. 136, no 3, p. 031017-Article in journal (Refereed)
    Abstract [en]

    Splitter or baffle silencers are commonly used, for example, in heating ventilation and air conditioning (HVAC) systems and as inlet/outlet silencers on gas turbines. Another application is to reduce noise from the cooling fan inlet for large IC-engines. A splitter silencer can be seen as a periodic arrangement of parallel rectangular absorbers, which can be placed in a rectangular duct. The noise reduction afforded by parallel splitters depends not only on the physical properties of the lining but also upon the angle of incidence of the impinging sound waves, and the splitter and duct dimensions. In this paper, the potential of using splitters made of microperforated plates (MPPs) is investigated, with a particular focus on cooling fan inlet/outlet applications.

  • 13.
    Allam, Sabry
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Noise control for cooling fans on heavy vehicles2012In: Noise Control Engineering Journal, ISSN 0736-2501, E-ISSN 2168-8710, Vol. 60, no 6, p. 707-715Article in journal (Refereed)
    Abstract [en]

    In this paper two different objects for fan passive noise control have been examined: heat exchangers and inlet/outlet parallel splitter silencers based on micro-perforated panels. The first object is theoretically and experimentally examined while the second is only examined experimentally. Throughout this paper two measurement methods were used. The ISO 15186-1:2000 to test the acoustic transmission for a diffuse field and plane wave testing in a duct of a sample cut from each heat exchanger type. Based on an anisotropic equivalent fluid model a theoretical model for the heat exchanger acoustic transmission is presented. A new type of splitter silencers based on micro-perforated plates, which can add damping up 10-20 dB in the frequency range of interest (<5 kHz), are also presented.

  • 14.
    Bodin, Olle
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx). KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Wang, Yue
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx). KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx). KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    LES of the Exhaust Flow in a Heavy-Duty Engine2014In: Oil & gas science and technology, ISSN 1294-4475, E-ISSN 1953-8189, Vol. 69, no 1, p. 177-188Article in journal (Refereed)
    Abstract [en]

    The flow in the exhaust port and the exhaust manifold of a heavy-duty Diesel engine has been studied using the Large Eddy Simulation approach. Some of the flow characteristics in these components are: flow unsteadiness and separation combined with significant geometry-induced secondary flow motion. Detailed analysis of these features may add understanding which can be used to decrease the flow losses and increase the eciency of downstream components such as turbochargers and EGR coolers. Few LES studies of the flow in these components have been conducted in the past and this, together with the complexity of the flow are the motivations for this work. This paper shows that in the exhaust port, even global parameters like total pressure losses are handled better by LES than RANS. Flow structures of the type that afect both turbine performance and EGR cooler efficiency are generated in the manifold and these are found to vary significantly during the exhaust pulse. This paper also clearly illustrates the need to make coupled simulations in order to handle the complicated boundary conditions of these gas exchange components.

  • 15.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Nonlinear source characterisation techniques for IC-engines2012In: 19th International Congress on Sound and Vibration 2012, ICSV 2012, 2012, p. 2442-2449Conference paper (Refereed)
    Abstract [en]

    A source characterization model for IC-engines, which can take weakly nonlinear source properties into account, is developed in the paper. It is based on so called polyharmonic distortion modeling, used for nonlinear characterization of microwave systems. Comparisons are made with the results from linear source models and another previously published weakly nonlinear source model. The results show that the new nonlinear impedance matrix model gives improvements in the prediction of sound pressure levels in the exhaust system.

  • 16.
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    The effect of speed variation on in-duct source data determination2014In: 21st International Congress on Sound and Vibration 2014, ICSV 2014, 2014, p. 2395-2401Conference paper (Refereed)
    Abstract [en]

    Experimental acoustic source characterization is used for IC-engines and fluid machines connected to duct or pipe systems. Information about the engine as an acoustic source is needed to calculate insertion loss of mufflers or the level of radiated sound. The source model used in the low frequency plane wave range is often the linear time invariant 1 -port model. The acoustic source data is obtained from experimental tests or from 1 -D CFD codes describing the engine gas exchange process. Multi-load methods and especially the two-load method are most commonly used to extract the source data. The IC-engine is a high level acoustic source and in most cases not completely linear. The real part of the measured source impedance sometimes has negative values which is un-physical. This effect has been attributed to non-linearity and source time variation. Another possible explanation could be speed variation giving measurement errors especially for higher harmonics. In the present paper this effect is studied by re-visiting source data experiments for IC-engine exhausts and comparing the outcome of different methods for extracting the amplitude and phase of the pressure in terms of frequency components or engine orders.

  • 17.
    Bodén, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Zhou, Lin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Acoustic Properties of an In-Duct Orifice Subjected to Bias Flow and High Level Acoustic Excitation2012In: Proceedings of the 10th International conference on Flow-Induced Vibration (& Flow-Induced Noise): FIV2012, Dublin, Ireland, 3-6 July 2012 FLOW-INDUCED VIBRATION, 2012, p. 187-193Conference paper (Refereed)
    Abstract [en]

    This paper experimentally investigates the acousticproperties of an orifice with bias flow under medium andhigh sound level excitation. The test included no bias flowand two bias speeds for three different frequencies. Experimentalresults are compared and discussed with theory.It is shown that bias flow makes the acoustic propertiesmuch more complex compared theory and with theno bias flow case, especially when velocity ratio betweenacoustic particle velocity and mean flow velocity is nearunity.

  • 18.
    Bodén, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Zhou, Lin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    An experimental study of the effect of flow and high level acoustic excitation on the acoustic properties of perforates and orifices2013In: 20th International Congress on Sound and Vibration 2013, ICSV 2013: Volume 3, 2013, International Institute of Acoustics and Vibrations , 2013, p. 2545-2552Conference paper (Refereed)
    Abstract [en]

    Perforates are for instance used in mufflers for automotive applications and in acoustic liners for aircraft engines. In these applications they are often exposed to high level acoustic excitation in combination with grazing or bias flow. The paper is based on an experimental study of the nonlinear properties of these types of samples without mean grazing or bias flow as well as on a study of an orifice with bias flow under medium and high sound level excitation. The effect of grazing flow is discussed based on data from the literature. It is known from previous studies that high level acoustic excitation at one frequency will change the acoustic impedance of perforates at other frequencies, thereby changing the boundary condition seen by the acoustic waves. This effect could be used to change the impedance boundary conditions and for instance increase the absorption. It could obviously also pose a problem for the correct modeling of sound transmission through ducts lined with such impedance surfaces. Experimental results are compared to a quasi-stationary model. The effect of the combination of frequency components and phase in the excitation signal is studied. The bias flow tests included different flow speeds for different frequencies. The level of acoustic excitation is varied from much smaller to larger than the mean flow velocity. It is shown that bias flow makes the acoustic properties more complex compared to the no bias flow case, especially when the velocity ratio between acoustic particle velocity and mean flow velocity is near unity.

  • 19.
    Canton, Jacopo
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Mechanics.
    Örlü, Ramis
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx). KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Linear stability of the flow in a toroidal pipe2015In: 9th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2015, TSFP-9 , 2015Conference paper (Refereed)
    Abstract [en]

    While hydrodynamic stability and transition to turbulence in straight pipes - being one of the most fundamental problems in fluid mechanics - has been studied extensively, the stability of curved pipes has received less attention. In the present work, the first (linear) instability of the canonical flow inside a toroidal pipe is investigated as a first step in the study of the related laminar-turbulent transition process. The impact of the curvature of the pipe, in the range 8 e [0.002,1], on the stability properties of the flow is studied in the framework of linear stability analysis. Results show that the flow is indeed modally unstable for all curvatures investigated and that the wave number corresponding to the critical mode depends on the curvature, as do several other features of this problem. The critical modes are mainly located in the region of the Dean vortices, and are characterised by oscillations which are symmetric or antisymmetric as a function of the curvature. The neutral curve associated with the first bifurcation is the result of a complex interaction between isolated modes and branches composed by several modes characterised by a common structure. This behaviour is in obvious contrast to that of straight pipes, which are linearly stable for all Reynolds numbers.

  • 20.
    Ceci, Alessandro
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Gojon, Romain
    KTH, School of Engineering Sciences (SCI), Mechanics. ISAE-SUPAERO, Toulouse, France.
    Mihaescu, Mihai
    KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx). KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics. KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Large Eddy Simulations for Indirect Combustion Noise Assessment in a Nozzle Guide Vane Passage2018In: Flow Turbulence and Combustion, ISSN 1386-6184, E-ISSN 1573-1987, Flow, Turbulence and Combustion, ISSN 1386-6184, p. 1-13Article in journal (Refereed)
    Abstract [en]

    The combustion noise in aero-engines is known to originate from two different sources. First, the unsteady heat release in the combustion chamber generates the direct combustion noise. Second, hot and cold spots of air generated by the combustion process are convected and accelerated by the turbine stages and give rise to the so-called indirect combustion noise. The present work targets, by using a numerical approach, the generation mechanism of indirect combustion noise for a simplified geometry of a turbine stator passage. Periodic temperature fluctuations are imposed at the inlet, permitting to simulate hot and cold packets of air coming from the unsteady combustion. Three-dimensional Large Eddy Simulation (LES) calculations are conducted for transonic operating conditions to evaluate the blade acoustic response to the forced temperature perturbations at the inlet plane. Transonic conditions are characterized by trailing edge expansion waves and shocks. It is notably shown that their movement can be excited if disturbances with a particular frequency are injected in the domain.

  • 21.
    Du, Lin
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx). Beijing University of Aeronautics and Astronautics, China.
    Holmberg, Andreas
    Karlsson, Mikael
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Sound amplification at a rectangular T-junction with merging mean flows2016In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 367, p. 69-83Article in journal (Refereed)
    Abstract [en]

    This paper reports a numerical study on the aeroacoustic response of a rectangular T-junction with merging mean flows. The primary motivation of the work is to explain the high sound amplification, recently seen experimentally, when introducing a small merging bias flow. The acoustic results are found solving the compressible Linearized Navier-Stokes Equations (LNSEs) in the frequency domain, where the base flow is first obtained using RANS with a k-epsilon turbulence model. The model predicts the measured scattering data well, including the amplitude and Strouhal number for the peak amplification, if the effect of eddy viscosity damping is included. It is found that the base flow changes significantly with the presence of a small bias flow. Compared to pure grazing flow a strong unstable shear layer is created in the downstream main duct starting from the T-junction trailing edge. This means that the main region of vortex-sound interaction is moved away from the junction to a downstream region much larger than the junction width. To analyze the sound amplification in this region Howe's energy corollary and the growth of acoustic density are used.

  • 22.
    Du, Lin
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Sun, X.
    Effect of flapping frequency on aerodynamics of wing in freely hovering flight2015In: Computers & Fluids, ISSN 0045-7930, E-ISSN 1879-0747, Vol. 117, p. 79-87Article in journal (Refereed)
    Abstract [en]

    The two-dimensional incompressible Navier-Stokes equations are solved using the immersed boundary method. The wing is driven to translate in the horizontal direction and rotate periodically to emulate the wing motion of a fruit fly in normal hovering flight, while the motion in the vertical direction responds passively to the action of the wing aerodynamic lift and weight of the insect body. The insect body is modeled by a point mass. It is shown that flapping wing cannot produce required lift to maintain stable hovering flight in specified range with low flapping frequencies, if the insect weight is equivalent to the averaged wing lift in one cycle on the assumption of zero vertical velocity. The vertical velocity influences the instantaneous angle of attack of the hovering wing, which results in the variation in aerodynamics of the wing. The insect may experience fluctuating hovering flight with a reduced weight when the flapping frequency is low. The fluctuating amplitude decreases with increasing flapping frequency. The efficiency of hovering flight is also a problem of concern.

  • 23.
    Du, Lin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Using micro-perforated plates to realize a silencer based on the Cremer impedance2014In: Proceedings of Forum Acusticum, European Acoustics Association (EAA), 2014Conference paper (Refereed)
    Abstract [en]

    Current trends for IC-engines are driving the development of more efficient engines with higher specific power. This is true for both light and heavy duty vehicles and has led to an increased use of charging. The charging can be both in the form of a single or multi-stage turbo-charger driven by exhaust gases or via a directly driven compressor. In both cases a possible noise problem can be a strong Blade Passing Frequency (BPF) typically in the kHz range and above the plane wave range. In this paper a novel type of compact dissipative silencer developed especially to handle this type of problem is described. The silencer is based on a combination of a micro-perforated tube backed by a locally reacting cavity. The combined impedance of micro-perforate and cavity is chosen to match the theoretical optimum known as the Cremer impedance at the mid-frequency in the frequency range of interest. Due to the high damping achieved at the Cremer optimum (hundreds of dB/m) it is easy to create a compact silencer with a significant damping (say >40 dB) in a range larger than an octave. Several principles are presented to determine the parameters of micro-perforate and cavity. The numerical results indicate that, following the principles, a silencer with broad-band damping can be achieved.

  • 24.
    Du, Lin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Åbom, Mats
    KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Karlsson, Mikael
    KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Knutsson, M.
    Modelling of Acoustic Resonators Using the Linearized Navier Stokes Equations2016Conference paper (Refereed)
    Abstract [en]

    To tune the acoustics of intake systems resonators are often used. A problem with this solution is that the performance of these resonators can be affected a lot by flow. First, for low frequencies (Strouhal-numbers) the acoustic induced vorticity across a resonator inlet opening will create damping, which can reduce the efficiency. Secondly, the vorticity across the opening can also change the end-correction (added mass) for the resonator, which can modify the resonance frequency. However, the largest problem that can occur is whistling. This happens since the vortex-sound interaction across a resonator opening for certain Strouhal-numbers will amplify incoming sound waves. A whistling can then be created if this amplified sound forms a feedback loop, e.g., via reflections from system boundaries or the resonator. To analyse this kind of problem it is necessary to have a model that allows for both sound and vorticity and their interaction. This means using a convected wave equation type of model is not sufficient. A better approach is to apply the linearized Navier Stokes equations, which will give a full model of the vortex-sound effects. In this paper an effort to apply this approach on a set of generic resonators is described. Besides the numerical results comparisons with experiments are also presented.

  • 25. El Nemr, Y.
    et al.
    Veloso, R.
    Girstmair, J.
    Kabral, Raimo
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Schutting, E.
    Dumböck, O.
    Ludwig, C.
    Mirlach, R.
    Masrane, A.
    Koutsovasilis, P.
    Experimental investigation of transmission loss in an automotive turbocharger compressor under ideal and real engine operating conditions2017In: 12th European Conference on Turbomachinery Fluid Dynamics and Thermodynamics, ETC 2017, KTH Royal Institute of Technology, 2017Conference paper (Refereed)
    Abstract [en]

    Acoustic transmission losses are expected to occur over the turbocharger compressor, especially along its rotating wheel section. Experiments on the acoustic characteristics of automotive turbocharger compressors were performed to investigate this acoustic transmission loss behavior. Two different rotor sizes were acoustically investigated considering approximately the same performance characteristics of the compressors. The investigated variants passed through two phases of measurements: The first phase was performed under ideal operating conditions involving a steady non-pulsating flow on an acoustic component test rig for turbochargers. Whereas the second phase was conducted under real engine operating conditions including pulsating flow of a modern 6-cylinder gasoline engine on an engine test rig. Comparisons between the two measurement phases show a considerable agreement between the two test rig setups for different operating conditions.

  • 26.
    Fjällman, Johan
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Exhaust flow pulsation effect on radial turbine performance2015In: 11th European Conference on Turbomachinery Fluid Dynamics and Thermodynamics, ETC 2015, European Conference on Turbomachinery (ETC) , 2015Conference paper (Refereed)
    Abstract [en]

    In the current vehicle manufacturing world the chase for a better fuel economy and better driveability is in high gear. One way of doing so is to investigate and optimize the turbocharger. In this paper the flow in a radial turbine of a passenger car turbocharger has been analysed by Large Eddy Simulations. The current simulations have investigated the effects of changing the inlet pulse frequency and inlet pulse shape on turbine's performance parameters (e.g. efficiency, shaft power, pressure distributions). Three different engine speeds and two different pulse shapes were chosen to be compared and analysed. With the total mass flow per pulse being constant for all cases there is a clear dependence of both pulse shape and frequency when it comes to e.g. wheel momentum. Higher frequency increases the peak momentum more than the minimum level. A reduction in pulse duration also increases peak momentum more than the minimum.

  • 27.
    Ford, C. L.
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Winroth, Marcus
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx). KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Alfredsson, P. Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx). KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Development of a pressure based vortex-shedding meter: measuring unsteady mass-flow in variable density gases2016In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 27, no 8, article id 085901Article in journal (Refereed)
    Abstract [en]

    An entirely pressure-based vortex-shedding meter has been designed for use in practical time-dependent flows. The meter is capable of measuring mass-flow rate in variable density gases in spite of the fact that fluid temperature is not directly measured. Unlike other vortex meters, a pressure based meter is incredibly robust and may be used in industrial type flows; an environment wholly unsuitable for hot-wires for example. The meter has been tested in a number of static and dynamic flow cases, across a range of mass-flow rates and pressures. The accuracy of the meter is typically better than about 3% in a static flow and resolves the fluctuating mass-flow with an accuracy that is better than or equivalent to a hot-wire method.

  • 28.
    Gundmalm, Stefan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Cronhjort, Andreas
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Ångström, Hans-Erik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Divided Exhaust Period: Effects of Changing the Relation between Intake, Blow-Down and Scavenging Valve Area2013In: SAE International Journal of Engines, ISSN 1946-3936, Vol. 6, no 2, p. 739-750Article in journal (Refereed)
    Abstract [en]

    In a previous paper we showed the effects of applying the Divided Exhaust Period (DEP) concept on two heavy-duty diesel engines, with and without Exhaust Gas Recirculation (EGR). Main findings were improved fuel consumption due to increased pumping work, improved boost control and reduced residual gas content. However, some limitations to the concept were discovered. In the case of high rates of short route EGR, it was apparent that deducting the EGR flow from the turbine manifold impaired optimal valve timing strategies. Furthermore, for both of the studied engines it was clear that the size and ratio of blow-down to scavenging valve area is of paramount importance for engine fuel efficiency. In this paper, the DEP concept has been studied together with a long route EGR system. As expected it gave more freedom to valve timing strategies when driving pressure for EGR is no longer controlled with the valve timing, as in the short route case. However, when evaluating different combinations of intake, blow-down and scavenging valve area, the optimal relation proves to be strongly dependent on the current EGR system and EGR rates. Hence, for different engine setups the trade-off between total intake and total exhaust area needs to be re-evaluated for optimal engine fuel efficiency. This paper also presents general trends in how different valve timing strategies and EGR rates affect both pumping work and boost pressure.

  • 29.
    Heide, Jakob
    et al.
    KTH.
    Karlsson, Mikael
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Altimira, Mireia
    KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Numerical Analysis of Urea-SCR Sprays under Cross-Flow Conditions2017In: SAE technical paper series, ISSN 0148-7191, Vol. 2017-March, no MarchArticle in journal (Refereed)
    Abstract [en]

    Selective Catalytic Reduction (SCR) of NOx through injection of Urea-Water-Solution (UWS) into the hot exhaust gas stream is an effective and extensively used strategy in internal combustion engines. Even though actual SCR systems have 95-96% de-NOx efficiency over test cycles, real driving emissions of NOx are a challenge, proving that there is room for improvement. The efficiency of the NOx conversion is highly dependent on the size of UWS droplets and their spatial distribution. These factors are, in turn, mainly determined by the spray characteristics and its interaction with the exhaust gas flow. The main purpose of this study is to numerically investigate the sensitivity to the modelling framework of the evaporation and mixing of the spray upstream of the catalyst. The dynamics of discrete droplets is handled through the Lagrangian Particle Tracking framework, with models that account for droplet breakup and coalescence, turbulence effects, and water evaporation. All simulations have been run in the commercial code Ansys Fluent 16.0. Experimental validation of droplet size distribution is carried out through PDPA measurements. Through the present study we have identified suitable modelling setup that provides accurate results with a competitive computational cost. Results also show the importance of accounting for the effects of evaporation and turbulent fluctuations in the droplet phase.

  • 30.
    Holmberg, Andreas
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Karlsson, Mikael
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Aeroacoustics of rectangular T-junctions subject to combined grazing and bias flows - An experimental investigation2015In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 340, p. 152-166Article in journal (Refereed)
    Abstract [en]

    Scattering matrices are determined experimentally and used to study the low amplitude interaction, between the acoustic and the hydrodynamic fields in a T-junction of rectangular ducts. In particular, combinations of grazing and bias flows are investigated in the study. It is observed that for all flow combinations, waves incident on the junction at the downstream side only are attenuated, while waves incident at the other branches may be amplified or attenuated, depending on the Strouhal number. When bias in flow is introduced to a grazing flow, there is first an increase and then a decrease in both amplification and attenuation, as the bias in-flow Mach number is increased. Comparing with T-junctions of circular ducts, the interaction is stronger for rectangular duct junctions.

  • 31.
    Holmberg, Andreas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Kierkegaard, Axel
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Weng, Chenyang
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    A frequency domain linearized Navier-Stokes method including acoustic damping by eddy viscosity using RANS2015In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 346, p. 229-247Article in journal (Refereed)
    Abstract [en]

    In this paper, a method for including damping of acoustic energy in regions of strong turbulence is derived for a linearized Navier-Stokes method in the frequency domain. The proposed method is validated and analyzed in 2D only, although the formulation is fully presented in 3D. The result is applied in a study of the linear interaction between the acoustic and the hydrodynamic held in a 2D T-junction, subject to grazing flow at Mach 0.1. Part of the acoustic energy at the upstream edge of the junction is shed as harmonically oscillating disturbances, which are conveyed across the shear layer over the junction, where they interact with the acoustic field. As the acoustic waves travel in regions of strong shear, there is a need to include the interaction between the background turbulence and the acoustic field. For this purpose, the oscillation of the background turbulence Reynolds stress, due to the acoustic Field, is modeled using an eddy Newtonian model assumption. The time averaged flow is first solved for using RANS along with a k-epsilon turbulence model. The spatially varying turbulent eddy viscosity is then added to the spatially invariant kinematic viscosity in the acoustic set of equations. The response of the 2D T-junction to an incident acoustic field is analyzed via a plane wave scattering matrix model, and the result is compared to experimental data for a T-junction of rectangular ducts. A strong improvement in the agreement between calculation and experimental data is found when the modification proposed in this paper is implemented. Discrepancies remaining are likely due to inaccuracies in the selected turbulence model, which is known to produce large errors e.g. for flows with significant rotation, which the grazing flow across the T-junction certainly is A natural next step is therefore to test the proposed methodology together with more sophisticated turbulence models.

  • 32.
    Holmberg, Andreas
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Kierkegaard, Axel
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Weng, Chenyang
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    A linearized Navier-Stokes method including turbulence damping2013In: 19th AIAA/CEAS Aeroacoustics Conference, 2013Conference paper (Refereed)
    Abstract [en]

    In this paper, a method for including damping of acoustic energy in regions of strong turbulence is derived for a linearized Navier-Stokes method in the frequency domain. The result is applied in a study of the linear interaction of the acoustic and the hydrodynamic field in a 2D T-junction, subject to grazing flow at Mach 0.1. As the acoustic waves travel in regions of strong shear, there is a need to include the interaction between the background turbulence and the acoustic field. For this purpose, the oscillation of the background turbulence Reynold's stress, due to the acoustic field, is modeled using an eddy Newtonian model assumption. The time averaged flow is first solved for using RANS along with a k-ε turbulence model. The spatially varying turbulent viscosity is then added to the spatially invariant kinematic viscosity in the acoustic set of equations. The response of the 2D T-junction to an incident acoustic field is analyzed via a plane wave scattering matrix model, and the result is compared to experimental data for a T-junction of rectangular ducts. A strong improvement in the agreement between calculation and experimental data is found when the modification proposed in this paper is implemented.

  • 33.
    Holmberg, Andreas
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx). KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx). KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Karlsson, M.
    Aeroacoustics of rectangular T-junctions subject to combined grazing and bias flows - An experimental investigation2013In: 19th AIAA/CEAS Aeroacoustics Conference, 2013Conference paper (Refereed)
    Abstract [en]

    Experimentally determined scattering matrices are used to study the low-amplitude interaction between the acoustic and the hydrodynamic fields in a T-junction of rectangular ducts. In particular, combinations of grazing and bias flows are investigated in the study. Common for all flow combinations is that waves incident on the junction at the downstream side are only attenuated, while waves incident at the other branches may be amplified or attenuated, depending on the Strouhal number. When bias in-flow is introduced to a grazing flow, there is first an increase and then a decrease in both amplification and attenuation, as the bias in-flow Mach number is increased. Comparing with T junctions of circular ducts, the interaction is stronger for rectangular duct junctions.

  • 34. Hynninen, A.
    et al.
    Turunen, R.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Acoustic source data for medium speed IC-engines2011In: 18th International Congress on Sound and Vibration 2011 (ICSV 18), 2011, p. 811-818Conference paper (Refereed)
    Abstract [en]

    Knowledge of the acoustic source characteristics of internal combustion engines (IC-engines) is of great importance when designing the exhaust duct system and its components to withstand the resulting dynamic loads and to reduce the exhaust noise emission. Number of studies has been published earlier on the low frequency in-duct exhaust noise of high speed engines. The goal of the present study is to investigate the medium speed IC-engine acoustic source characteristics numerically and experimentally not only in the low frequency - plane wave range but also in the high frequency range. The low frequency acoustic source characteristics were predicted by simulating the acoustic multi-load measurements using a one-dimensional process simulation code. The engine model used in the one-dimensional process simulations was validated with measurements. In this study, it is shown that the low frequency in-duct exhaust noise of a medium speed IC-engine can be predicted quite accurately by using a onedimensional process simulation code. The high frequency source data is estimated by averaging the measured acoustic pressures with different methods. According to this study, using the simple cross spectra averaging method instead of two microphone method to estimate the induct downstream acoustic power of medium speed IC-engine exhaust noise seems promising. The simulation of the high frequency exhaust noise is beyond this study.

  • 35. Hynninen, A.
    et al.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Acoustic two-port simulation model for the particle oxidation catalyst (POC®)2014In: INTERNOISE 2014 - 43rd International Congress on Noise Control Engineering: Improving the World Through Noise Control, 2014Conference paper (Refereed)
    Abstract [en]

    The reduction of the exhaust noise from internal combustion engine (IC-engine) is mainly managed by proper silencer design, while less attention is paid to the acoustic performance of the after treatment devices (ATD). It is known from the earlier studies, that the transmission loss of a typical ATD unit can be quite significant. An ATD unit for diesel engines is classically assembled from several specific parts such as selective catalytic reducers (SCR), diesel oxidation catalysts (DOC) and diesel particulate filters (DPF). One new alternative to the conventional DPF is the particle oxidation catalyst (POC®). The substrate used in the POC-X type filter consists of fine, corrugated metallic wire mesh screens piled askew and rolled into a cylindrical shape. In this paper an acoustic two-port simulation model for POC-X is sought starting from the classical Kirchhoff solution for prediction of the acoustic wave attenuation in narrow channels. According to experimental studies, correction factors to the narrow channel two-port model are proposed.

  • 36. Hynninen, A.
    et al.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Estimating the high frequency in-duct sound power using sound pressures at the duct wall2013In: 20th International Congress on Sound and Vibration 2013, ICSV 2013: Volume 3, 2013, International Institute of Acoustics and Vibrations , 2013, p. 2553-2559Conference paper (Refereed)
    Abstract [en]

    When studying the acoustic wave propagation in a Channel, the frequency range can be divided to the low frequency plane wave range and to the high frequency range with non-plane waves. In the low frequency range the wave propagation is one-dimensional and the governing equations are rather simple. The larger the duct the lower the frequency limit of the non-plane waves. Therefore taking into account also the three-dimensional acoustic wave propagation is important especially when considering the duct systems used in large structures, e.g., medium speed internal combustion engines (IC-engines), fans, or compressors. Harsh environment and unmovable structures restrict the use of standardized noise measuring methods. To characterize the medium speed IC-engine exhaust noise in situ, the in-duct sound pressures are measured using wall mounted transducers. Then the source sound power is estimated from the propagating sound pressures, which is the power based approach. The power based approach is only valid in frequency averaged sense and therefore the source power must be defined in one-third octave frequency bands, for example. One way to estimate the source sound power in the high frequency range, is to extend the classical plane wave formulation by defining the one-third octave frequency band weighting factors for different excitation types. The aim of this study is to define these weighting factors using finite element method (FEM) simulations of a test duct with non-reflecting terminations. The sound pressures at the duct wall were compared to the sound pressures at the duct end for randomized multi-modal excitations. From statistics, the one-third octave band weighting factors and their reliability were estimated.

  • 37. Hynninen, A.
    et al.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Procedure to estimate the in-duct sound power in the high frequency range with non-plane waves2012In: 41st International Congress and Exposition on Noise Control Engineering 2012, INTER-NOISE 2012: Volume 10, 2012, ASME Press, 2012, p. 8026-8036Conference paper (Refereed)
    Abstract [en]

    The acoustic characterization of fluid machines, e.g., internal combustion engines, compressors, or fans is of great importance when designing the connected duct systems and its silencers. For machines connected to large ducts where also the non-plane wave range is important, for instance large diesels and gas turbines, a suitable way to characterize the source is to determine the sound power under reflection free conditions. For the low frequency plane wave range in-duct sound power can be measured with the widely used two microphone method. The goal of this study is to investigate how, starting from the two-microphone approach, a suitable wall mounted microphone configuration can be defined and used to estimate the propagating in-duct sound power also beyond the plane wave range. For this purpose an acoustic source test-rig was built and numerical simulations were also conducted. The in-duct sound power from monopole, dipole, and quadrupole source types was determined using twelve wall mounted microphones and cross-spectra averaging methods. The in-duct results were compared against sound power measured using the reverberation room method (ISO 3741). Based on the simulations and the experimental results the best microphone positions and weighting factors were determined.

  • 38. Hynninen, A.
    et al.
    Åbom, Mats.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Procedure to estimate the in-duct sound power in the high frequency range with non-plane waves2012In: ASME 2012 Noise Control and Acoustics Division Conference at InterNoise 2012, ASME Press, 2012, p. 181-191Conference paper (Refereed)
    Abstract [en]

    The acoustic characterization of fluid machines, e.g., internal combustion engines, compressors, or fans is of great importance when designing the connected duct systems and its silencers. For machines connected to large ducts where also the non-plane wave range is important, for instance large diesels and gas turbines, a suitable way to characterize the source is to determine the sound power under reflection free conditions. For the low frequency plane wave range in-duct sound power can be measured with the widely used two microphone method. The goal of this study is to investigate how, starting from the two-microphone approach, a suitable wall mounted microphone configuration can be defined and used to estimate the propagating in-duct sound power also beyond the plane wave range. For this purpose an acoustic source test-rig was built and numerical simulations were also conducted. The in-duct sound power from monopole, dipole, and quadrupole source types was determined using twelve wall mounted microphones and cross-spectra averaging methods. The in-duct results were compared against sound power measured using the reverberation room method (ISO 3741). Based on the simulations and the experimental results the best microphone positions and weighting factors were determined.

  • 39.
    Hynninen, Antti
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. VTT Technical Research Centre of Finland Ltd.
    Turunen, R.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Acoustic source data for medium speed IC-engines2012In: Journal of Vibration and Acoustics-Transactions of the ASME, ISSN 1048-9002, E-ISSN 1528-8927, Vol. 134, no 5, p. 051008-Article in journal (Refereed)
    Abstract [en]

    Knowledge of the acoustic source characteristics of internal combustion engines (IC-engines) is of great importance when designing the exhaust duct system and its components to withstand the resulting dynamic loads and to reduce the exhaust noise emission. The goal of the present study is to numerically and experimentally investigate the medium speed IC-engine acoustic source characteristics, not only in the plane wave range but also in the high frequency range. The low frequency acoustic source characteristics were predicted by simulating the acoustic multiload measurements by using a one-dimensional process simulation code. The low frequency in-duct exhaust noise of a medium speed IC-engine can be quite accurately predicted. The high frequency source data is estimated by averaging the measured acoustic pressures with different methods; using the simple cross-spectra averaging method seems promising in this instance.

  • 40. Hynninen, Antti
    et al.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Acoustic Source Characterization for Prediction of Medium Speed Diesel Engine Exhaust Noise2014In: Journal of Vibration and Acoustics-Transactions of the ASME, ISSN 1048-9002, E-ISSN 1528-8927, Vol. 136, no 2, p. 021008-Article in journal (Refereed)
    Abstract [en]

    To achieve reliable results when simulating the acoustics of the internal combustion engine (IC-engine) exhaust system and its components, the source characteristics of the engine must be known. In the low frequency range only plane waves propagate and then one-port source data can be determined using, for example, the acoustic multiload method. For the medium speed IC-engines used in power plants and ships, the exhaust duct noise often needs to be analyzed up to 10 kHz, i.e., far beyond the plane wave range, and it is then more appropriate to use acoustic power to characterize the source. This power should ideally be measured under reflection-free conditions in the exhaust duct. The results from an earlier study showed that a suitable way to characterize the source for any frequency is to determine the in-duct sound power by extending the plane wave formulation with frequency band power weighting factors. The aim of this study is to apply this high frequency range method in situ to a real test engine. Another aim is to define, theoretically, how to combine the source data in the low frequency plane wave range with those in the high frequency nonplane wave range using a source sound power formulation.

  • 41. Hynninen, Antti
    et al.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Determination of in-duct sound power beyond the plane wave range using wall-mounted microphones2015In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 99, p. 24-30Article in journal (Refereed)
    Abstract [en]

    When studying the acoustic wave propagation in a duct, the frequency range can be divided into the low frequency plane wave range and the high frequency range with non-plane waves. In the low frequency range, the wave propagation is one-dimensional and the governing equations are rather simple. The larger the duct, the lower the frequency limit of the non-plane waves. Therefore, also taking into account the three-dimensional acoustic wave propagation is important, especially when considering the duct systems used in large machines. In practice often a harsh environment and immobile structures restrict the use of standardized noise measuring methods. For instance to characterize the exhaust noise of medium speed internal combustion engines (IC-engines) in situ, the in-duct sound pressures are measured using wall-mounted microphones. Then the low frequency range source sound power can be estimated by wave decomposition ("two-microphone method"). Often a three-microphone array is used to cover a sufficiently large frequency range. One way to formulate the sound pressure and sound power relationship in the high frequency range is to weight the sound pressures at the duct wall in one-third octave bands. The aim of this study is to extend the classical plane wave formulation by determining these weighting factors, so that a three-microphone array also can be used beyond the plane wave range. The results from numerical approach are compared to experimental data.

  • 42. Hynninen, Antti
    et al.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Simulation of the particle oxidation catalyst POC (R) acoustics2014In: Noise Control Engineering Journal, ISSN 0736-2501, E-ISSN 2168-8710, Vol. 62, no 5, p. 368-374Article in journal (Refereed)
    Abstract [en]

    The reduction of the exhaust noise from internal combustion engine (IC-engine) is mainly managed by proper silencer design, while less attention is paid to the acoustic performance of the after treatment devices (ATD). It is known from the earlier studies, that the transmission loss of a typical ATD unit can be quite significant. An ATD unit for diesel engines is classically assembled from several specific parts such as selective catalytic reducers (SCR), diesel oxidation catalysts (DOC) and diesel particulate filters (DPF). One new alternative to the conventional DPF is the particle oxidation catalyst (POC (R)). The POC (R) substrate studied in this paper is of type POC-X, which consists of fine, corrugated metallic wire mesh screens piled askew and rolled into a cylindrical shape. In this paper acoustic two-port simulation models for POC-X are proposed. First model is built up starting from the classical Kirchhoff solution for prediction of the acoustic wave attenuation in narrow channels. According to experimental studies, correction factors to the narrow channel two-port model are proposed. Second model is derived by treating the filter as a lumped acoustic resistance, dependent on the flow resistivity coefficients obtained from the pressure drop measurements.

  • 43.
    Jyothishkumar, V
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx). KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Semlitsch, Bernhard
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx). KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx). KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Numerical Flow Analysis in a Centrifugal Compressor near Surge Condition2013In: 43rd AIAA Fluid Dynamics Conference and Exhibit, 2013 / [ed] AIAA, AIAA , 2013Conference paper (Refereed)
    Abstract [en]

    This numerical study presents data relevant to the flow characteristics inside of a centrifugal compressor, at design and near-surge conditions. The main objectives were to characterize the flow structures and the associated instabilities near the stall point (prior to surge) and to contrast the obtained results against data acquired for a design operation condition. Generally, the operational range of compressors is limited at low mass flow rates by development of instabilities, e.g. stall and rotating stall. Such conditions lead to breakdown of the operability of the compressor, with flow reversal in the wheel passage. This results in large mass flow variations and pressure fluctuations within the compressor, lowering the compressor efficiency and pressure ratio. Large vibratory stresses are induced in the blade under such off-design operating conditions, affecting the blade life duration. Compressor stall and rotating stall are frequently regarded as “precursors” to the more damaging surge instability.  The flow fields under design and off-design operating conditions are calculated using the Large Eddy Simulation (LES) approach.  The complete geometry (360 degree) of the compressor is considered during analysis. It includes the ported shroud, the compressor wheel, the vaneless diffuser, the volute, and the exit pipe. The computationally expensive transient sliding mesh technique is used in order to capture the interaction between the wheel, the flow, and the stationary components of the compressor. The LES data are validated against available experimental measurements obtained under the same operating conditions (i.e. at design and off-design). The calculated frequency spectra when the compressor operated near-by the surge line indicated the presence of the rotating stall.

  • 44.
    Kabral, Raimo
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Bodén, Hans
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Elnady, T.
    Determination of liner impedance under high temperature and grazing flow conditions2014In: 20th AIAA/CEAS Aeroacoustics Conference, 2014Conference paper (Refereed)
    Abstract [en]

    Acoustic liners have traditionally been used to reduce fan noise from the aircraft engine intake. To increase noise reduction there are now plans to also put liners in hot stream parts of the engine. In order to test liners under as realistic conditions as possible there has been a large development in inverse techniques for determination of liner impedance under grazing flow conditions, so called impedance eduction techniques. Testing under hot stream conditions has received smaller attention. This paper discusses techniques for measuring liner impedance under hot stream conditions and present some results obtained for single degree of freedom Helmholtz resonator liners with different configurations. It could be argued that the main effect of high temperatures is a change of medium properties such as: density, viscosity and speed of sound. If this is true the high temperature impedance could be predicted by scaling from the result at cold conditions. This is investigated in the paper by comparing measured results from liner impedance models available in the literature.

  • 45.
    Kabral, Raimo
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx). KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Du, Lin
    KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Knutsson, M.
    Optimization of Compact Non-Fibrous Silencer for the Control of Compressor Noise2016In: SAE technical paper series, ISSN 0148-7191, Vol. 2016-June, no JuneArticle in journal (Refereed)
    Abstract [en]

    The concept of IC engine downsizing is a well-adapted industry standard, enabling better fuel conversion efficiency and the reduction of tailpipe emissions. This is achieved by utilizing different type of superchargers. As a consequence, the additional charger noise emission, at the IC engine inlet, can become a problem. In order to address such problem, the authors of this work have recently proposed a novel dissipative silencer for effective and robust noise control of the compressor. Essentially, it realizes an optimal flow channel impedance, referred to as the Cremer impedance. This is achieved by means of a straight flow channel with a locally reacting wall consisting of air cavities covered by an acoustic resistance, e.g., a micro-perforated panel (MPP). In this paper, an improved optimization method of this silencer is presented. The classical Cremer impedance model is modified to account for mean flow dependence of the optimal wave number. This modified model leads to significantly different impedance values compared to the classical model and consequently, the high damping of the classical model (hundreds of dB/m) is further increased. Moreover, the modeling herein, is performed by solving the convective wave equation, vital for accounting mean flow effects. The presented model is finally validated by experimental results included in the paper.

  • 46.
    Kabral, Raimo
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    El Nemr, Yasser
    Ludwig, Carlos
    Mirlach, Robert
    Koutsovasilis, Panagiotis
    Masrane, A
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Experimental acoustic characterization of automotive twin-scroll turbine2017In: 12th European Conference on Turbomachinery Fluid Dynamics and Thermodynamics, ETC 2017, KTH Royal Institute of Technology, 2017Conference paper (Other academic)
    Abstract [en]

    The present paper focuses on the experimental determination of automotive twin-scroll turbine acoustic performance. The unique test-rig for automotive turbocharger acoustics at KTH CCGEx laboratory is further developed to enable testing of modern twin-scroll turbines under controlled laboratory conditions. It is shown how the passive acoustic properties of such turbines can be accurately characterized by means of an acoustic three-port formulation. Governing equations along with the new test-rig design are presented and discussed in detail. Furthermore, complementary results from the first experimental determination of twin-scroll turbine acoustic three-port data are presented.

  • 47.
    Kabral, Raimo
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Rammal, H.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Acoustical methods for investigating turbocharger flow instabilities2013In: SAE technical paper series, ISSN 0148-7191, Vol. 4, p. 2013-01-1879-Article in journal (Refereed)
    Abstract [en]

    In order to increase the internal combustion engine efficiency turbocharging is today widely used. The trend, in modern engine technology, is towards higher boost pressures while keeping the combustion pressure raise relatively small. The turbocharger surge occurs if the pressure at the outlet of the compressor is greater than it can maintain, i.e., a reverse flow will be induced. In presence of such flow conditions instabilities will occur which can couple to incident acoustic (pressure) waves and amplify them. The main objective of the present work is to propose a novel method for investigation of turbocharger flow instabilities or surge precursors. The method is based on the determination of the acoustic two-port data. The active part of this data describes the sound generation and the passive part the scattering of sound. The scattering data will contain information about flow-acoustic interaction and amplification of sound that could occur close to surge. Here the existence of such amplification will be investigated for a compressor operating at different operating points including points near the surge line. In addition the generated sound for reflection-free conditions is also investigated on both the up- and downstream side. All the measurements have been carried out in the unique CCGEx test rig for two-port testing of turbo-compressors.

  • 48.
    Kabral, Raimo
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Investigation of flow-acoustic interaction in automotive turbocharger2014In: Proceedings of ISMA 2014 - International Conference on Noise and Vibration Engineering and USD 2014 - International Conference on Uncertainty in Structural Dynamics, KU Leuven , 2014, p. 1327-1331Conference paper (Refereed)
    Abstract [en]

    In IC engine design, the surge condition of a turbocharger is a well-recognized phenomena. As the resulting global fluctuation of mass flux in the intake system is hazardous, the implemented safety margins are large. In order to, reduce such safety margins and employ turbochargers more efficiently, it is of interest to investigate acoustic fields as a possible surge triggering mechanism. Regardless the increasing relevance of this topic today, only few publications exist addressing the acoustics of turbochargers from the perspective of surge prediction and triggering. In the present paper acoustical properties of an automotive turbocharger are experimentally studied at the limit of stable operation as well as under normal operating conditions in the unique CCGEx test rig at KTH. The full two-port data including passive and active parts is determined and utilized to investigate the possible coupling effects between unstable flow and acoustic fields. The local flow instabilities, occurring at the limit of globally stable operation, can interact with the acoustic field and amplify incident sound waves which eventually can lead to an unstable situation and surge. This effect can be studied from the passive two-port data. In addition the active data can be used to find the occurrence of compact correlated sources in the compressor such as rotating stall a pre-cursor of surge.

  • 49.
    Kabral, Raimo
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Investigation of turbocharger compressor surge inception by means of an acoustic two-port model2018In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 412, p. 270-286Article in journal (Refereed)
    Abstract [en]

    The use of centrifugal compressors have increased tremendously in the last decade being implemented in the modern IC engine design as a key component. However, an efficient implementation is restricted by the compression system surge phenomenon. The focus in the investigation of surge inception have mainly been on the aerodynamic field while neglecting the acoustic field. In the present work a new method based on the full acoustic 2-port model is proposed for investigation of centrifugal compressor stall and surge inception. Essentially, the compressor is acoustically decoupled from the compression system, hence enabling the determination of sound generation and the quantification of internal aero-acoustic coupling effects, both independently of the connected pipe system. These frequency dependent quantities are indicating if the compressor is prone to self-sustained oscillations in case of positive feedback when installed in a system. The method is demonstrated on experimentally determined 2-port data of an automotive turbocharger centrifugal compressor under a variety of realistic operating conditions.

  • 50.
    Kalpakli, Athanasia
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Experimental study of turbulent flows through pipe bends2012Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis deals with turbulent flows in 90 degree curved pipes of circular cross-section. The flow cases investigated experimentally are turbulent flow with and without an additional motion, swirling or pulsating, superposed on the primary flow. The aim is to investigate these complex flows in detail both in terms of statistical quantities as well as vortical structures that are apparent when curvature is present. Such a flow field can contain strong secondary flow in a plane normal to the main flow direction as well as reverse flow.

    The motivation of the study has mainly been the presence of highly pulsating turbulent flow through complex geometries, including sharp bends, in the gas exchange system of Internal Combustion Engines (ICE). On the other hand, the industrial relevance and importance of the other type of flows were not underestimated.

    The geometry used was curved pipes of different curvature ratios, mounted at the exit of straight pipe sections which constituted the inflow conditions. Two experimental set ups have been used. In the first one, fully developed turbulent flow with a well defined inflow condition was fed into the pipe bend. A swirling motion could be applied in order to study the interaction between the swirl and the secondary flow induced by the bend itself. In the second set up a highly pulsating flow (up to 40 Hz) was achieved by rotating a valve located at a short distance upstream from the measurement site. In this case engine-like conditions were examined, where the turbulent flow into the bend is non-developed and the pipe bend is sharp. In addition to flow measurements, the effect of non-ideal flow conditions on the performance of a turbocharger was investigated.

    Three different experimental techniques were employed to study the flow field. Time-resolved stereoscopic particle image velocimetry was used in order to visualize but also quantify the secondary motions at different downstream stations from the pipe bend while combined hot-/cold-wire anemometry was used for statistical analysis. Laser Doppler velocimetry was mainly employed for validation of the aforementioned experimental methods.

    The three-dimensional flow field depicting varying vortical patterns has been captured under turbulent steady, swirling and pulsating flow conditions, for parameter values for which experimental evidence has been missing in literature.

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