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  • 1.
    Bodin, Olle
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Analysis of transonic shock/boundary-layer interaction by spectral methodsArticle in journal (Other academic)
  • 2.
    Bodin, Olle
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Wang, Yue
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Analysis of the flow structures in the exhaust manifold of a heavy duty engineArticle in journal (Other academic)
  • 3.
    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.

  • 4.
    Chandramouli, Sathyanarayanan
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Gojon, Romain
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Fridh, Jens
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Numerical characterization of entropy noise with a density based solver2017In: 12th European Conference on Turbomachinery Fluid Dynamics and Thermodynamics, ETC 2017, KTH Royal Institute of Technology, 2017Conference paper (Refereed)
    Abstract [en]

    In this work, dbnsTurbFoam, a new coupled density based solver, written in the framework of FOAM-EXTEND, is considered. The solver is first assessed on two canonical compressible flow scenarios, namely the Sod's shock tube and the ONERA S8 transonic channel. Results are compared with analytical formulations and experiments, respectively. 2-D Unsteady Reynolds Averaged Navier-Stokes simulations and 3-D Large Eddy Simulations of the flow within the passages of a geometrically simplified High Pressure Turbine Nozzle Guide Vane are then performed. Results are compared against experimental data in order to justify the geometrical simplifications made. Finally, the case of a sinusoidal temperature forcing at the inlet is considered in order to study the phenomenon of indirect combustion noise. Notably, the impact of the forcing on the vortex shedding dynamics and on the losses is discussed.

  • 5. de Luzan, Charles Farbos
    et al.
    Chen, Jie
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Khosla, Sid M.
    Gutmark, Ephraim
    Computational study of false vocal folds effects on unsteady airflows through static models of the human larynx2015In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 48, no 7, p. 1248-1257Article in journal (Refereed)
    Abstract [en]

    Compressible large eddy simulation is employed to numerically investigate the laryngeal flow. Symmetric static models of the human larynx with a divergent glottis are considered, with the presence of false vocal folds (FVFs). The compressible study agrees well with that of the incompressible study. Due to the high enough Reynolds number, the flow is unsteady and develops asymmetric states downstream of the glottis. The glottal jet curvature decreases with the presence of FVFs or the ventricular folds. The gap between the FVFs stretches the flow structure and reduces the jet curvature. The presence of FVFs has a significant effect on the laryngeal flow resistance. The intra-glottal vortex structures are formed on the divergent wall of the glottis, immediately downstream of the separation point. The vortices are then convected downstream and characterized by a significant negative static pressure. The FVFs are a main factor in the generation of stronger vortices, and thus on the closure of the TVFs. The direct link between the FVFs geometry and the motion of the TVFs, and by extension to the voice production, is of interest for medical applications as well as future research works. The presence of the FVFs also changes the dominant frequencies in the velocity and pressure spectra.

  • 6.
    Duwig, Christophe
    et al.
    Energy Sciences, Lund University.
    Gherman, Bogdan
    Energy Sciences, Lund University.
    Mihaescu, Mihai
    Energy Sciences, Lund University.
    Salewski, Mirko
    Energy Sciences, Lund University.
    Fuchs, Laszlo
    Energy Sciences, Lund University.
    Numerical Study of Thermo-acoustic Waves Generation by a Swirling Flame Using a New Approach Based on large eddy simulation2005In: Volume 2: Turbo Expo 2005: Power for Land, Sea, and Air (GT2005), 2005, p. 67-75Conference paper (Refereed)
    Abstract [en]

    The new challenge of the Gas Turbine industry is to develop new technologies for meeting electricity demand growth and reducing harmful emissions. Thus, a better understanding of the combustion phenomenon and an improvement in simulation capabilities are needed. In this paper, we present a new technique that is computationally efficient, for capturing the thermo-acoustic waves in low Mach number combustors. The idea is to utilize the fact that the acoustic related pressure fluctuations are small as compared to the dynamic pressure. Semi-compressible LES of reacting flow is performed and while the pressure perturbations related to the acoustic-wave propagation are handled separately. The equations are solved individually while allowing interaction between the two systems. The technique has been applied to the study of the generation and propagation of thermo-acoustic waves in a combustion chamber. A sensitivity analysis is presented and most important instability modes are identified.

  • 7.
    Fjällman, Johan
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Analysis of 3 Dimensional Turbine Flow by using Mode Decomposition Techniques2014In: Proceedings of the ASME Turbo Expo, 2014, p. GT2014-26963-Conference paper (Refereed)
    Abstract [en]

     Today one of the most popular ways of lowering the fuel consumption and emissions of the Internal Combustion Engine (ICE) is by downsizing the engine. Downsizing means that the swept volumes of the cylinders are decreased; this lowers the frictional and thermal losses. By combining the downsizing with a well matched turbocharger system the performance is preserved while the advantages are retained. Since more and more of the development work is being performed by simulations there is an increasing need for more accurate methods. These methods are more complex and require more resources than the simpler, faster and more robust models used today. In this study Large Eddy Simulations (LES) of the unsteady flow in a radial turbine designed for a gasoline ICE has been performed and analysed. The flow inside the turbine is highly 3 dimensional, pulsating and characterized by secondary flow motions and high curvatures. All these are reasons for which the method of choice should be LES. LES is able to resolve a large range of scales and capture the flow dynamics. The considered case concerns a non-pulsating flow condition but with engine like mass flow and temperature. Post-processing tools based on Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) are used to analyse the large amount of LES based flow data. The POD method is used to investigate the energy content of the dominant, large structures present in the flow. The DMD method on the other hand is used to reveal the flow structures responsible for specific frequencies found in the flow field. Preliminary data show a fair agreement between experimental data and LES results in terms of predicting the turbine performance parameters.

  • 8.
    Fjällman, Johan
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Analysis of Secondary Flow Induced by a 90 Bend in a Pipe Using Mode Decomposition Techniques2013Conference paper (Refereed)
    Abstract [en]

    In this study unsteady simulations of the flow through and after a 90 pipe bend has been performed by Large Eddy Simulations (LES). In the passenger car engine there is an abundance of pipes and pipe bends. Since pipes and bends are often situated upstream of important engine components the flow in these needs to be well predicted. This entails that there is a need for accurate pipe flow simulations in order to ensure that the inflow conditions, to the e.g. cylinders or turbocharger, are as close to the experimental values as possible. The flow field is further studied by the use of Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD). It has been found that there is a low frequency oscillation in the strength of the alternately dominant dean vortex at the exit of the pipe bend. This phenomenon is analysed and the mechanism for it is discussed.

  • 9.
    Fjällman, Johan
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Effects of inlet geometry on turbine performanceManuscript (preprint) (Other academic)
    Abstract [en]

    In this study comparisons have been performed between gas-stand experiments,Unsteady Reynolds Averaged Navier-Stokes (URANS) simulations, and LargeEddy Simulations (LES) of the ow through a radial turbine of a turbochargerdesigned for an internal combustion engine. The long term goal for the projectis to improve the prediction capabilities for the simpler computational modelsused by industry in the research and development of new products. At thepresent stage the eects of using simplied geometries and methods for turbineperformance predictions are assessed. Additionally, data obtained from URANScalculations is compared against experimental data and against unsteady LESresults. The comparisons are made in order to evaluate the employed methodologies,to know when to use simplied models with reasonable accuracy, as wellas to justify the use of more advanced methods when the models are inadequate.It was found out that the LES results are closer to the gas-stand experimentsthan the URANS predictions are.

  • 10.
    Fjällman, Johan
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Effects of Pulsation Frequency and Pulse Shape on Turbine PerformanceManuscript (preprint) (Other academic)
    Abstract [en]

      The current paper studies the pulsating flow in the exhaust manifold and turbine of a passenger car engine. The study focuses on three engine RPMs and two different pulse shapes, one normal shape and one shorter DEP like shape. By simulating different valve strategies one can investigate how to maximize the available exhaust flow energy to the turbine. The simulations have been performed with the Large Eddy Simulation (LES) method with boundary conditions received from GT-Power simulations. The study focuses on kinetic energy and turbine torque analysis of the incoming flow and of the flow in the turbine wheel region. It is found that the pulse shape is affecting the wheel torque significantly and that the kinetic energy entering the wheel region is different depending on which cylinder fired.

  • 11.
    Fjällman, Johan
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics.
    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.

  • 12.
    Fjällman, Johan
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Numerical investigations of a free turbulent jet after a 90° pipe bendManuscript (preprint) (Other academic)
    Abstract [en]

    In this study the ow out of pipe after a 90pipe bend has been investigated byperforming Large Eddy Simulations. Comparisons of velocity proles, ow eldsand power spectral densities have been performed between numerical simulationsand experiments. Pipe bends exists in many industrial applications especiallyin the internal combustion engine. Performing accurate and predictive pipe owsimulations is becoming more important when more of the development work isbeing performed by simulations. The long term goal of this project is to helpwith development of simpler models that are faster to run but give the sameaccuracy. During this study it was found that the method used works well bothin predicting mean values and in resolving dynamic motions such as vortexswitching. LES calculations without a SGS model has been proven to work wellwith ows of this type as long as the grid resolution is suciently ne.

  • 13.
    Fjällman, Johan
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    On the Importance of Turbulence Modelling of the Flow after a 90 Pipe BendManuscript (preprint) (Other academic)
    Abstract [en]

    The flow in a free jet after a 90 pipe bend has been investigated by Large Eddy Simulations (LES) and Reynolds Averaged Navier-Stokes (RANS) simulations. The numerical results for the mean velocity profiles, flow fields, and power spectral densities have been compared to experimental data. The results show that LES has been able to predict the mean components of the velocity field and in resolving dynamic motions such as vortex switching. LES without an explicit SGS model (termed as ILES in the following) has been found to work well with flows of this type as long as the grid resolution is sufficiently fine. Different Sub-Grid-Scale (SGS) models have also been used. LES with different SGS models result in very similar results when a fine enough grid is used. The ILES approach also gives reasonably accurate results for the mean values even for coarser grids.

  • 14. Gherman, B. G.
    et al.
    Malael, I.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Porumbel, I.
    Jet pump optimization through Reynolds averaged: Navier-Stokes simulation analysis2015In: 22nd AIAA Computational Fluid Dynamics Conference, American Institute of Aeronautics and Astronautics, 2015Conference paper (Refereed)
    Abstract [en]

    The paper presents the aerodynamic analysis of an air jet pump by means of Reynolds Averaged Navier-Stokes (RANS) simulations. A baseline configuration, reproducing an existing jet pump is first analysed from the perspective of overall mean compressible flow behaviour, turbulence production and mixing, and efficiency performance. Several constructive solutions are proposed in order to achieve enhanced mixing and efficiency performance. All the cases are investigated for the same operating condition of interest. As a result of the numerical analysis, two solutions are selected as potential improved constructive solutions in terms of mixing and efficiency performance. It is intended to complement the study by further experimental measurements for the baseline set-up and for the two selected configurations, in order to assess their actual performance and to validate the numerical data.

  • 15.
    Gojon, Romain
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Baier, Florian
    Univ. of Cincinnati.
    Gutmark, Ephraim
    Aerospace Engineering, University of Cincinnati.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Temperature effects on the aerodynamic and acoustic fields of a rectangular supersonic jet2017In: Proceedings of the 55th AIAA Aerospace Sciences Meeting, American Institute of Aeronautics and Astronautics, 2017, p. 19-, article id AIAA2017-0002Conference paper (Refereed)
    Abstract [en]

    In the first part of the paper, a modified artificial dissipation mechanism permitting to perform Large-Eddy Simulations of highly compressible flows is proposed. This dissipation mechanism is evaluated using one linear 2-D test case and two non-linear 2-D test cases. In the second part, the flow and acoustic near-field of rectangular supersonic jets are explored using compressible LES based on this modified artificial dissipation mechanism. At the exit of a converging diverging rectangular nozzle of aspect ratio 2 and of design Mach number 1.5, the jets are overexpanded. Four simulations with four different temperature ratios ranging from 1 to 3 are performed in order to characterize the effect of the temperature on the aerodynamic and aeroacoustic fields of the jets. The geometry of the nozzle and the exit conditions are chosen in order to match those in the experimental study conducted at the University of Cincinnati. It is shown that the total number of cells in the shock cell structure decreases with the increase of the temperature ratio. However, the temperature does not influence the size of the first shock cell and the linear decrease of the shock cell size in the downstream direction. The Overall Sound Pressure Levels are then plotted along the minor and major axis. It is seen that the intensity of the screech feedback mechanism increases with the Temperature Ratio. Moreover, for JetTR2.5 and JetTR3, the strong flapping motion of the jet along the minor axis due to the screech feedback mechanism seems to yield to an asymmetric organization of the Mach wave radiation. The convection velocity of the turbulent structures in the jet shear layers along the minor axis is then studied. Once normalized by the jet exit velocity, the convection velocity is shown to decrease with the jet temperature ratio. In the last part of the paper, the near- and far-field acoustic are studied. In the near-field, screech tones which frequencies are consistent with both experimental data and a theoretical model are observed. In the far-field, four acoustic components typical of non-ideally supersonic jets are observed, namely the screech noise, the broadband shock-associated noise, the mixing noise and the Mach wave noise. Their directivities and frequencies are in agreement with experimental results and models.

  • 16.
    Gojon, Romain
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Gutmark, E.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    On the response of a rectangular supersonic jet to a near-field located parallel flat plate2017In: 23rd AIAA/CEAS Aeroacoustics Conference, 2017, American Institute of Aeronautics and Astronautics, 2017Conference paper (Refereed)
    Abstract [en]

    In this paper, the flow and acoustic fields of a rectangular over-expanded supersonic jet interacting with a parallel plate are investigated using compressible LES. The jet exits from a converging diverging rectangular nozzle of aspect ratio 2 and of design Mach number 1.5. Four simulations with four different distances between the lower inner lip of the minor axis of the rectangular jet and the plate ranging from 0 to 3 equivalent diameters are performed. The geometry of the nozzle, the positions of the plate, and the exit conditions are chosen in order to match those in an experimental study conducted at the University of Cincinnati. Snapshots and mean velocity fields are first presented. A good agreement with the PIV experimental measurements is found. The Overall Sound Pressure Levels are then plotted along the minor and major axis. In a previous paper, the corresponding free jet has been found to undergo a strong flapping motion along the minor axis due to the screech feedback mechanism. In the present study, it is seen that the intensity of the screech feedback mechanism increases for some distances and decreases for some others compared to the one in the corresponding free jet. A study of the jets shear-layers is then proposed first by looking at two points space-time cross correlation of the axial velocity. The convection of the turbulent is thus studied. Then, two points space-time cross correlation of the pressure along the jets shear-layers are proposed and an amplification of the aeroacoustic feedback mechanism leading to screech noise is observed in the lower jet shear-layers for two cases. It is also observed that the screech feedback mechanism establishes mainly between the nozzle lips and the end of the tenth shock cell. The acoustic loading on the plate is finally studied. As pointed out in a previous study, the flapping motion of the jet at the screech frequency seems to yield to an asymmetric organization of the Mach wave radiation also at the screech frequency. Those organized Mach waves impinge in the plate and propagate back to the jet, exciting the shear-layer at the screech frequency. This will amplify the screech mechanism in the lower jet shear-layer. However, this amplification happens only for some nozzle-to-plate distances. Indeed, the screech mechanism leads to the formation of a standing wave pattern in terms of pressure loading at the screech frequency on the plate. There are regions with high amplitude, meaning the acoustic loading is organized mainly at the screech frequency, and regions with low amplitude, which means the acoustic loading is not organized mainly at the screech frequency. The amplification then depends on the location of the standing wave compared to the overall acoustic loading on the plate. If a region of high amplitude of the standing wave pattern coincide with the region of maximal acoustic loading, there is amplification of the screech mechanism.

  • 17.
    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.

  • 18. Kerres, B.
    et al.
    Cronhjort, Andreas
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Stenlaas, O.
    A Comparison of On-Engine Surge Detection Algorithms using Knock Accelerometers2017In: SAE technical paper series, ISSN 0148-7191, Vol. 2017-OctoberArticle in journal (Refereed)
    Abstract [en]

    On-engine surge detection could help in reducing the safety margin towards surge, thus allowing higher boost pressures and ultimately low-end torque. In this paper, experimental data from a truck turbocharger compressor mounted on the engine is investigated. A short period of compressor surge is provoked through a sudden, large drop in engine load. The compressor housing is equipped with knock accelerometers. Different signal treatments are evaluated for their suitability with respect to on-engine surge detection: the signal root mean square, the power spectral density in the surge frequency band, the recently proposed Hurst exponent, and a closely related concept optimized to detect changes in the underlying scaling behavior of the signal. For validation purposes, a judgement by the test cell operator by visual observation of the air filter vibrations and audible noises, as well as inlet temperature increase, are also used to diagnose surge. The four signal treatments are compared with respect to their reliability as surge indicator and the time delay between surge onset and indication. Results show that the signal power in the surge frequency band has reasonably good properties as surge indicator. The normal Hurst exponent is problematic, since periodic vibrations from engine firing dominate the scaling behavior. Root mean square and the above mentioned scaling exponent do not measure vibrations caused by surge directly, but rather the reduction in housing vibrations due to the engine load drop. Nevertheless, it was found to be possible to design an indicator that gives good results based on the change in scaling behavior.

  • 19.
    Kerres, Bertrand
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.). Competence Center for Gas Exchange.
    Cronhjort, Andreas
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics. Competence Center for Gas Exchange.
    A Comparison of On-Engine Surge Detection Algorithms Using Knock AccelerometersManuscript (preprint) (Other academic)
    Abstract [en]

    On-engine surge detection could help in reducing the safety margintowards surge, thus allowing higher boosting pressures and ultimatelylow-end torque. In this paper, experimental data from a truckturbocharger compressor mounted on the engine is investigated. Ashort period of compressor surge is provoked through a sudden, largedrop in engine load. The compressor housing is equipped with knockaccelerometers. Different signal treatments are evaluated for theirsuitability with respect to on-engine surge detection: the signal rootmean square, the power spectral density in the surge frequency band,the recently proposed Hurst exponent, and a closely related conceptoptimized to detect changes in the underlying scaling behavior of thesignal. For validation purposes, a visual observation of the air filtervibrations are also used to diagnose surge. The four signal treatmentsare compared with respect to their reliability as surge indicator andthe time delay between surge onset and indication. Results show thatthe signal power in the surge frequency band has reasonably goodproperties as surge indicator. The normal Hurst exponent isproblematic, since periodic vibrations from engine firing dominatethe scaling behavior. Root mean square and the above mentionedscaling exponent do not measure vibrations caused by surge directly,but rather the reduction in housing vibrations due to the engine loaddrop; nevertheless, it was found to be possible to design an indicatorthat gives good results based on the change in scaling behavior.

  • 20.
    Kerres, Bertrand
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.). 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.). 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).
    Experimental investigation of upstream installation effects on the turbocharger compressor map2016In: The 12th International Conference on Turbochargers and Turbocharging, London, UK, 17-18 May, 2016, 2016Conference paper (Refereed)
    Abstract [en]

    This paper experimentally investigates the effects of an upstream bended pipe on the compressor speedline slopes and surge line. Different orientation angles for the incoming bended pipe relative to the compressor scroll are investigated. The tests were carried out on a cold gas stand on a passenger car sized turbocharger. A bended pipe upstream of the compressor leads to an increase of the surge margin. This effect does not depend on the orientation of the bend. Comparisons with a straight inlet with artificially generated pressure losses indicate that the increase in operating range is an effect of the pressure losses generated in the bend.

  • 21.
    Kerres, Bertrand
    et al.
    KTH, School of Industrial Engineering and Management (ITM).
    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.
    Gancedo, Matthieu
    Univ. of Cincinnati.
    Gutmark, Ephraim
    Aerospace Engineering, University of Cincinnati.
    Optimal Pressure based Detection of Compressor Instabilities using the Hurst Exponent2017In: SAE International Journal of Engines, ISSN 1946-3936, E-ISSN 1946-3944, Vol. 10, no 4, p. 1917-1926Article in journal (Refereed)
    Abstract [en]

    The compressor surge line of automotive turbochargers can limit the low-end torque of an engine. In order to determine how close the compressor operates to its surge limit, the Hurst exponent of the pressure signal has recently been proposed as a criterion. The Hurst exponent quantifies the fractal properties of a time series and its long-term memory. This paper evaluates the outcome of applying Hurst exponent based criterion on time-resolved pressure signals, measured simultaneously at different locations in the compression system. Experiments were performed using a truck-sized turbocharger on a cold gas stand at the University of Cincinnati. The pressure sensors were flush-mounted at different circumferential positions at the inlet of the compressor, in the diffuser and volute, as well as downstream of the compressor. Results show that the previously identified threshold value distinguishing between surge and stable operation when the analysis was carried out for a different and smaller compressor can be used also for this much larger compressor. The investigation concerning the sensor locations reveals that pressure sensors at the outlet or shortly upstream the volute tongue give the clearest distinction between fully stable operation and operation close to the surge line. Further investigations show that as currently implemented, the criterion would need a minimum sampling duration of 500 ms and sampling frequency of 512 Hz. An extended algorithm based on distinguishing between a mono- and multifractal pressure signal is shown to have potential as an early warning indicator.

  • 22.
    Kerres, Bertrand
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Nair, Vineeth
    KTH.
    Cronhjort, Andreas
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
    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.
    Analysis of the Turbocharger Compressor Surge Margin Using a Hurst-Exponent-based Criterion2016In: SAE International Journal of Engines, ISSN 1946-3936, E-ISSN 1946-3944, Vol. 9, no 3Article in journal (Refereed)
    Abstract [en]

    Turbocharger compressors are limited in their operating range at low mass flows by compressor surge, thus restricting internal combustion engine operation at low engine speeds and high mean effective pressures. Since the exact location of the surge line in the compressor map depends on the whole gas exchange system, a safety margin towards surge must be provided. Accurate early surge detection could reduce this margin. During surge, the compressor outlet pressure fluctuates periodically. The Hurst exponent of the compressor outlet pressure is applied in this paper as an indicator to evaluate how close to the surge limit the compressor operates. It is a measure of the time-series memory that approaches zero for anti-persistence of the time series. That is, a Hurst exponent close to zero means a high statistical preference that a high value is followed by a low value, as during surge. Maps of a passenger-car sized turbocharger compressor with inlet geometries that result in different surge lines are measured on a cold gas stand. It is demonstrated that the Hurst exponent in fact decreases as the compressor moves towards surge, and that a constant value of the Hurst exponent can be used as a threshold for stable operation. Transient pressure signals of the compressor entering surge are analyzed in order to evaluate the time lag until surge can be detected using the Hurst exponent. Two surge cycles are usually needed to detect unstable operation. However, since the amplitude of these oscillations is relatively small for the first cycles, detection is possible before the oscillations grow into deep surge.

  • 23.
    Kerres, Bertrand
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.). KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Sanz, Sergio
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.). KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Sundström, Elias
    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).
    A Comparison of Performance Predictions between 1D Models and Numerical Data for a Turbocharger Compressor2017In: Proceedings of 12th European Conference on Turbomachinery Fluid dynamics and Thermodynamics ETC12, April 3-7, Stockholm, Sweden, KTH Royal Institute of Technology, 2017Conference paper (Refereed)
    Abstract [en]

    Compressor performance prediction models, based on integral conservation of mass, momentum and energy with empirical loss terms, are important tools in early design stages. Two such models from literature are compared to numerical results for an automotive turbocharger radial compressor with a vaneless diffuser and a volute. Results show that these models are less accurate than fully three-dimensional numerical RANS CFD calculations at low impeller speeds and choke, but can compete at high impeller speeds. Of the two impeller models, one gives a more accurate prediction than the other. The diffuser and volute models investigated here show large differences to the CFD calculations at off-design conditions. A comparison of the impeller loss terms to CFD entropy increase indicates also possibilities for improvement in the impeller models.

  • 24.
    Lagerström, Robert
    et al.
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Critical Success Factors in E-Learning for Project-Based Courses2014Conference paper (Refereed)
  • 25.
    Lim, Shyang Maw
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Dahlkild, Anders
    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).
    Exergy analysis on turbocharger radial turbine with heat transfer2017In: 12th European Conference on Turbomachinery Fluid Dynamics and Thermodynamics, ETC 2017, KTH Royal Institute of Technology, 2017Conference paper (Refereed)
    Abstract [en]

    Inconsistent results about heat transfer effects on performance and poor understanding of the aerothermodynamics loss mechanisms related to heat transfer in turbocharger turbine motivated this study. This study aimed to investigate the sensitivity of performance to heat loss and to quantify loss mechanisms associated with heat transfer in a turbine by using exergy analysis. A hybrid simulation methodology, i.e. Detached Eddy Simulation (DES) was used to compute the three-dimensional flow field of a turbine operating under hot gas stand continuous flow condition. Principal findings of this study were 1) Pressure ratio is less sensitive to heat loss as compared to turbine power, 2) Turbine power drop due to heat loss is relatively insignificant as compared to the exergy lost by heat transport and exergy destroyed by thermal irreversibilities, and 3) Assuming the most ideal isentropic gas expansion, more than 80% of the inflow exergy is unutilized in the investigated turbine system.

  • 26.
    Lim, Shyang Maw
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Dahlkild, Anders
    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).
    Wall Treatment Effects on the Heat Transfer in a Radial Turbine Turbocharger2016In: Springer Proceedings in Physics, Springer Science+Business Media B.V., 2016, p. 439-447Conference paper (Refereed)
    Abstract [en]

    Contradicting results about heat transfer effects on the performance of turbine turbocharger motivated this study. It was aimed to assess the effects that the wall treatment in a numerical sense has on the performance of a radial turbine of automotive turbocharger operating under a continuous flow condition. Adiabatic and non-adiabatic conditions were analyzed by using Unsteady Reynolds Averaged Navier-Stokes (URANS), Large Eddy Simulations (LES) and Detached Eddy Simulations (DES) approaches. When considering heat transfer, heat transfer loss at various locations is highly dependent on the near-wall modelling approach employed. Development of thermal boundary layer in the upstream region of turbine affects how the gas is convected in the downstream components, such as the scroll and the rotor. As long as the deviation in predicting thermal boundary layer does not affect the prediction of gas temperature at the inlet and outlet of the rotor, the difference in turbine power prediction by different near-wall modelling approaches was found to be small.

  • 27.
    Malla, Bhupatindra
    et al.
    School of Aerospace Systems, University of Cincinnati.
    Mihaescu, Mihai
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Kastner, Jeffrey
    School of Aerospace Systems, University of Cincinnati.
    Gutmark, Ephraim
    Aerospace Engineering, University of Cincinnati.
    Proper Orthogonal Decomposition on LES and PIV Data Sets from a Mach 0.9 Jet.2012In: 50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition / [ed] AIAA, AIAA , 2012, p. 12-Conference paper (Refereed)
    Abstract [en]

    This paper contains the complementary analysis of the results obtained through computational and experimental methods using the technique of Proper Orthogonal Decomposition (POD). A detailed study of the experimentally obtained flow field data using the method of POD has already been accomplished. The experimental data consists of the 2D visualization of the velocity field obtained using Particle Image Velocimetry (PIV). The computational process is initialized with the simulation of the 3D flow field using a steady state RANS flow solver. RANS is used as a platform to proceed towards capturing the unsteadiness of the flow field which is accomplished using the Large Eddy Simulation (LES). A significant match in the characteristics of the mode shapes has been observed, in both the axial and radial components of the velocity field, however, there is difference in the distribution of the energies over the modes. The LES predicts the energies to be higher at the lowest modes and the energy drop off rate is higher. On the contrary, PIV predicts lower energies at the first few modes, in comparison to the LES results, however the energy drop off rate is smaller.

  • 28.
    Mihaescu, Mihai
    Energy Sciences, Lund University.
    Computational Aeroacoustics Based on Large Eddy Simulation and Acoustic Analogies2005Doctoral thesis, monograph (Other academic)
    Abstract [en]

    The thesis presents a numerical method developed by the author and its applications for computing the generated sound by an unsteady flow field and its propagation. The full equations of motion for compressible and unsteady flows describe both flow field and sound generation and propagation. It is assumed that the flow variables can be decomposed into semi-compressible / incompressible components and inviscid, irrotational acoustic components. The present method is based on Large Eddy Simulation (LES) to compute the turbulent flow and an approach based on an inhomogeneous wave equation to compute the radiated acoustic field. In this way one can avoid the necessity for a very large computational effort associated with direct simulation of the near- and specially far- field sound generated by a turbulent flow. The governing equations are written in the form of a non-homogeneous wave equation for the acoustic fluctuation with acoustic sources on the right-hand side. The thesis includes the details of the coupling between the flow solver and the acoustic one, as well as the results for test cases employed to validate the numerical algorithm and the implemented boundary conditions. The method has been successfully applied to compute the near- and far- acoustic fields generated by various unsteady flows such as a round hot turbulent jet ejected from a pipe close to a solid boundary, coaxial turbulent non-isothermal jets (separate exhaust system), or the flow around a wind-turbine.

  • 29.
    Mihaescu, Mihai
    et al.
    Energy Sciences, Lund University.
    Fuchs, Laszlo
    Energy Sciences, Lund University.
    Sound Generated by an Unsteady Flow Field, Using a Hybrid Method2004In: Modelling Fluid Flow: The State of the Art, Springer-Verlag , 2004, 1, , p. 169-178p. 169-178Chapter in book (Refereed)
    Abstract [en]

    The compressible Navier-Stokes equations describe both flow field as well as sound generation. The classical acoustic theory uses the hypothesis that the part of the flow field, which is the source of the acoustic field, has distinct scales so that the acoustic waves do not interfere with the flow. Thus, the velocity vector, the pressure and the density are split into semi-compressible components and an inviscid, irrotational acoustical components. The paper includes the details of the coupling between the turbulent flow (based on Large Eddy Simulation) and the acoustical part (based on Lighthill's acoustic analogy). The approach is applied to the acoustics of a non-isothermal jet.

  • 30.
    Mihaescu, Mihai
    et al.
    Aerospace Systems, University of Cincinnati.
    Gutmark, Ephraim
    Aerospace Engineering, University of Cincinnati.
    Modeling of the Flow and Acoustical Field due to a Single Jet with Chevrons2007In: 43rd AIAA/ASME/SAE/ASEE Joint Propulsion Conference, 2007, p. 7372-7380Conference paper (Refereed)
    Abstract [en]

    The turbulent jets exhausting from jet engines are the main sources of aircraft noise. Finding new jet noise suppression methods and developing cheap and accurate jet noise prediction approaches was and is the major interest for many research groups. In the present paper the acoustic field generated by flow unsteadiness in an isothermal turbulent jet with forced mixers is determined using a hybrid approach. The computational domain includes in the first instance the near-field ”source” region and a small part of the acoustical region. The dynamics of the turbulent jet and its mixing with the surrounding air generate the acoustic sources that are calculated, on this restricted grid, by solving the flow field with Large Eddy Simulation (LES) approach. The sound radiated in the far-field is computed on a much larger domain by solving an inhomogeneous wave equation with acoustic source terms provided by near-field LES calculations. The flow and the acoustic data from the single jet case with chevrons are compared with those obtained from a circular jet, showing the acoustic benefit when chevrons are used on the nozzle.

  • 31.
    Mihaescu, Mihai
    et al.
    Aerospace Engineering, University of Cincinnati.
    Gutmark, Ephraim
    Aerospace Engineering, University of Cincinnati.
    Numerical Simulations of Jets Exhausting from Elliptic Nozzles without and with Conic Plug2008In: Proceedings of Int. Conf. on Jets, Wakes and Separated Flows, ICJWSF-2008, 2008Conference paper (Refereed)
    Abstract [en]

    Computational Fluid Dynamics was employed to model spatially developing turbulent jets issued from a low aspect ratio elliptic nozzle and from an elliptic plug nozzle. Results from Large Eddy Simulation and steady Reynolds-Averaged Navier-Stokes modeling of a benchmark elliptic jet exhausting from a 2:1 aspect ratio nozzle are compared. It was observed that only LES captured the axis-switching phenomenon. Further on, LES was used to calculate the flow exhausting from an elliptic plug nozzle. In this case the simulations predicted that a bifurcated jet is generated. The jet bifurcates just downstream of the center-body tip in the major-axis plane and the two potential core regions diverge as the jet spreads. The obtained data are presented in terms of instantaneous, time-averaged, and fluctuating quantities and are supported by experimental measurements.

  • 32.
    Mihaescu, Mihai
    et al.
    Aerospace Engineering, University of Cincinnati.
    Gutmark, Ephraim
    Aerospace Engineering, University of Cincinnati.
    Fuchs, Laszlo
    Energy Sciences, Lund University.
    Computational Aeroacoustics of the Coaxial Flow Exhaust System of a Gas Turbine Engine2007In: Volume 6: Turbo Expo 2007, Parts A and B, ASME , 2007, p. 1531-1539Conference paper (Refereed)
    Abstract [en]

    Jet engine noise is an environmental problem that needs to be addressed. Several methods to reduce the jet noise have been proposed in the last decades. The main issue is to find methods that reduce noise without causing considerable loss of thrust. Experimental and computational tools are mandatory in successfully reducingjet engine noise emissions. One of the challenging issues ofcomputing the jet engine noise is the presence of verylarge scales (associated with the wave length of the acousticwave) and at the same time also small scales that are responsible for the acoustical sources. In the field of Computational Aero-Acoustics (CAA) different hybrid approaches have been introduced to handle the different scales using problem specific models and methods.Here, a decomposition of flow variables is used that allowsseparation of flow and acoustic computations. Large Eddy Simulation approachis employed to compute the flow field and the acousticsources. An inhomogeneous wave equation is used to perform acousticcomputations. The paper investigates numerically the flow and the near-fieldacoustic data from a coaxial jet case with chevrons onthe core nozzle that are compared with those obtained froma baseline coaxial jet, showing the spatial character of the acoustic benefit when chevrons are used on the core nozzle.Comparisons in terms of sound pressure levels with experimental data performed with the same geometry show a good agreement.

  • 33.
    Mihaescu, Mihai
    et al.
    Aerospace Systems, University of Cincinnati.
    Gutmark, Ephraim
    Aerospace Engineering, University of Cincinnati.
    Khosla, Sid
    Otolaryngology, Head & Neck Surgery, University of Cincinnati-Medical Center.
    Scherer, Ronald
    Otolaryngology, Head & Neck Surgery, University of Cincinnati-Medical Center.
    Fuchs, Laszlo
    Energy Sciences, Lund University.
    Flow and Acoustics Simulations Based on LES and an Acoustic Analogy: an Application to Laryngeal Airflow2007In: 45th AIAA Aerospace Sciences Meeting 2007, 2007, p. 11141-11153Conference paper (Refereed)
    Abstract [en]

    The paper presents an efficient method for computational aeroacoustics applied to simulate the flow and the acoustics for a static laryngeal model considering the vocal folds widely open. The work analyses the whisper-like process defined as the sound generated by the turbulent glottal airflow in the absence of vocal fold vibration. A decomposition of the flow variables is used that allows separation of flow and acoustic computations. The approach consists in solving the low Mach number flow field by incompressible Large Eddy Simulation. This provides the possibility to compute the acoustic sources. The inhomogeneous wave equation derived from the fundamental equations of motion for a compressible fluid is employed to compute the acoustic field. The purpose of the study is to provide realistic numerical predictions of the flow patterns and the generated acoustic field in the glottis and the vocal tract regions.

  • 34.
    Mihaescu, Mihai
    et al.
    Aerospace Systems, University of Cincinnati.
    Gutmark, Ephraim
    Aerospace Engineering, University of Cincinnati.
    Szasz, Robert
    Energy Sciences, Lund University.
    Fuchs, Laszlo
    Energy Sciences, Lund University.
    Flow and Acoustics of a Coaxial Nozzle: a Sensitivity Study to the Inlet Boundary Conditions2006In: 44th AIAA Aerospace Sciences Meeting 2006, 2006, p. 7375-7393Conference paper (Refereed)
    Abstract [en]

    The jet noise generated by the high velocity hot stream exhausting from a jet engine represents a major component of the aircraft noise. Reductions in jet noise has been achieved by using high bypass turbo-fan engines. To solve numerically this problem the flow and acoustic fields generated by two coaxial jets are considered. Large Eddy Simulation (LES) is used to handle the non-isothermal turbulent flow field, while for the acoustic field a wave equation with source terms provided by the instantaneous LES is employed. The effects of the inlet boundary conditions on the flow and acoustics are assessed in this paper. A comparison of the computed mean flow field and the SPL with experimental data show excellent agreement at distances of over a few jet diameters downstream of the the jet exit plane. In the proximal part the agreement is less good. However, the discrepancy between the simulations and the experiments is less than the corresponding variations due to the uncertainties in the experimental boundary conditions.

  • 35.
    Mihaescu, Mihai
    et al.
    Aerospace Systems, University of Cincinnati.
    Gutmark, Ephraim
    Aerospace Engineering, University of Cincinnati.
    Szasz, Robert
    Energy Sciences, Lund University.
    Fuchs, Laszlo
    Energy Sciences, Lund University.
    Martens, Steven
    General Electric (GE) Aviation.
    Computational Aeroacoustics of a Separate Flow Exhaust System with Eccentric Inner Nozzle2007In: 45th AIAA Aerospace Sciences Meeting 2007, 2007, p. 28-39Conference paper (Refereed)
    Abstract [en]

    A major issue related to our modern way of life is the noise caused by jet engine powered airliners. Methods to reduce the jet noise were proposed in the last decades starting with the introduction of high bypass turbofan engines. A numerical investigation of flow and acoustics of a separate flow exhaust system is performed in the present paper. The goal is to investigate how the noise generated by a separate flow jet engine exhaust is influenced if the symmetry of the jet exhaust geometry is broken by having the inner nozzle and the center body off the center line axis of the fan nozzle. A decomposition of flow variables is used that allows separation of flow and acoustic computations. Large Eddy Simulation approach is employed to compute the flow field and the acoustic sources. The inhomogeneous wave equation is used to compute the acoustic near- and far-fields. Using this method, previous numerical studies of the symmetric (baseline) configuration showed good agreement between the computed data and the experimental results. Comparisons between the near- and far-field baseline concentric case and the computations obtained using the eccentric configuration are performed showing an acoustic benefit for the offset case.

  • 36.
    Mihaescu, Mihai
    et al.
    Aerospace Systems, University of Cincinnati.
    Harris, Christopher
    Aerospace Engineering, University of Cincinnati.
    Gutmark, Ephraim
    Aerospace Engineering, University of Cincinnati.
    Fuchs, Laszlo
    Energy Sciences, Lund University.
    Flow and Acoustics Characteristics of Chevron Nozzles in Coaxial Jets – LES and Acoustic Analogy Investigation2007In: 13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference), 2007, p. 12-Conference paper (Refereed)
    Abstract [en]

    In the last decades there has been significant interest in developing source-based jet noise suppression methods as well as developing jet noise prediction approaches that may involve modified geometry and complex flow fields. In this numerical study the acoustic field generated by flow unsteadiness in a non-isothermal coaxial turbulent jet with and without forced mixers on the core nozzle is determined using a hybrid approach. In the flow solver the Navier-Stokes equations are resolved using Large Eddy Simulation (LES) to model the turbulence. The acoustic solver is based on an inhomogeneous wave equation, where the instantaneous acoustic sources are computed from the LES data. The flow and the acoustic data from the coaxial jet case with chevrons on the core nozzle are compared with those obtained from a baseline coaxial jet, showing the spatial character of the acoustic benefit when forced mixers are used on the core nozzle. The computed results are compared with experimental data performed with the same geometry. The agreement between the two data sets in terms of sound pressure levels (SPLs) and noise directivity is very good.

  • 37.
    Mihaescu, Mihai
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Kastner, Jeffrey
    School of Aerospace Systems, University of Cincinnati.
    Gutmark, Ephraim
    Aerospace Engineering, University of Cincinnati.
    Tertiary flow effects on a co-axial ducted jet2012In: 50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition / [ed] AIAA, AIAA , 2012, p. AIAA 2012-0064-Conference paper (Refereed)
    Abstract [en]

    Long duct mixed flow exhaust systems operate as noise suppression devices under the concept that the surrounding secondary long duct shields some of the fine-scale turbulent mixing noise generated between the primary and secondary streams. Numerical results concerning a round co-axial ducted jet at Baseline (without tertiary flow effects) are compared against data obtained for two tertiary flow conditions of 0.15 and 0.30 co-flow Mach numbers (Mcf), respectively. The computations are carried out by using the Reynolds-Averaged Navier-Stokes (RANS) formulation with Realizable k-? turbulence model. At Baseline, comparisons between the computational predictions and Stereoscopic Particle Imaging Velocimetry (SPIV) experimental data just downstream of the nozzle exit show a good agreement. In the fully merged zone of the jet, self-similarity is achieved at the downstream axial location of x ~ 9D (Baseline case, Mcf = 0), where D is the diameter of the long duct nozzle’s exit. The tertiary flow increases the length of the potential core region while limiting the radial spread of the jet. With tertiary flow, self-similarity is achieved at x ~ 11D and at x ~ 13D for the co-flow Mach numbers (Mcf) of 0.15 and 0.30, respectively. When considering a tertiary flow of Mcf = 0.30, the maximum turbulence intensity levels in the outer shear layer of the jet decreased to about 20% of the baseline case.

  • 38.
    Mihaescu, Mihai
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Khosla, Sid
    Otolaryngology, Head & Neck Surgery, University of Cincinnati-Medical Center.
    Gutmark, Ephraim
    Aerospace Engineering, University of Cincinnati.
    Quantification of the false vocal-folds effects on the intra-glottal pressures using large eddy simulation2013In: Proceedings of Meetings on Acoustics: Volume 19, 2013, Acoustical Society of America (ASA), 2013, p. 1-8Conference paper (Refereed)
    Abstract [en]

    During the closing phase of the phonation cycle the true vocal-folds (TVF) have a convergent-divergent shape. The negative pressures generated by the flow through the glottal passage are producing closing forces acting on the TVFs. They can affect both vocal-fold vibration and voice production, since they can accelerate the closing phase. Large Eddy Simulation approach is used to investigate the intra-glottal forces generated solely by the flow during the closing phase. The influence of the gap between the false vocal-folds (FVFs) and the location of FVFs with respect to the TVFs are analyzed. Based on anatomical measurements, four different widths between the FVFs and two different distances between the true and false vocal-folds are investigated for the same trans-laryngeal pressure. The TVFs gap is kept constant. All cases exhibit a non-symmetric flow behavior in the mid-frontal plane. As the distance between the FVFs is decrease beyond a threshold value (still greater than glottal width), there is an increase in the magnitude of the closing forces acting on the TVFs. On the divergent slope of the glottis, these forces were found for some of the cases to be up to four times greater in magnitude as compared with the Baseline case.

  • 39.
    Mihaescu, Mihai
    et al.
    Aerospace Engineering, University of Cincinnati.
    Khosla, Sid
    Otolaryngology, Head & Neck Surgery, University of Cincinnati-Medical Center.
    Murugappan, Shanmugam
    Otolaryngology, Head & Neck Surgery, University of Cincinnati-Medical Center.
    Gutmark, Ephraim
    Aerospace Engineering, University of Cincinnati.
    Unsteady laryngeal airflow simulations of the intra-glottal vortical structures2010In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 127, no 1, p. 435-444Article in journal (Refereed)
  • 40.
    Mihaescu, Mihai
    et al.
    Aerospace Engineering, University of Cincinnati.
    Munday, David
    Aerospace Engineering, University of Cincinnati.
    Gutmark, Ephraim
    Aerospace Engineering, University of Cincinnati.
    Large Eddy Simulation for Turbulent Mixing in Elliptic Jets with Round Center-Body2009In: th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, AIAA , 2009Conference paper (Refereed)
    Abstract [en]

    Separate-flow exhaust nozzle systems generate jets from round nozzles that include a conical plug. The present research shows results of unsteady simulations of turbulent hot jets issued from elliptic nozzles with a conic center-body. Three geometrical configurations of the elliptic nozzle are investigated keeping the same conic plug. All designs considered were intended to match the jet stream exit area, mass flow, and thrust of an existing round conical nozzle. The first configuration in the study (C1@3:1AR) was designed with the expectation of producing a jet which would take on a 3:1 aspect ratio (AR) elliptic cross-section downstream of the center-body. For a round conical plug nozzle the inner surface of the nozzle towards exit is axisymmetric with reference to the nozzle center-line and conical. Naturally, the elliptic plug nozzle is not axisymmetric. In the major axis plane the inner surface of the elliptic nozzle towards the exit has a slope close to zero, while in the minor axis plane the slope is steeper that it would be for a corresponding round nozzle. This forces the flow stream towards the conic plug in the minor axis plane. It was observed that the 3:1AR elliptic plug nozzle (C1@3:1AR) generates a bifurcated jet. The second and the third elliptic plug nozzle geometries (C2@3:1ARnf and C3@2:1ARnf) were intended to find how the jet behavior is influenced by not forcing the flow towards the conic plug in the minor axis plane and by changing the aspect ratio of the elliptic plug nozzle to 2:1. Large Eddy Simulation (LES) approach was used for the turbulence flow modeling. In the major axis plane the largest jet spreading was found for the 3:1AR elliptic plug nozzle (C1@3:1AR), while in the minor axis plane the jet exhausting from the 2:1AR elliptic plug nozzle (C3@2:1ARnf) spread the most.

  • 41.
    Mihaescu, Mihai
    et al.
    Aerospace Engineering, University of Cincinnati.
    Murugappan, Shanmugam
    Otolargyngology, Head and Neck Surgery, University of Cincinnati-Medical Center.
    Gutmark, Ephraim
    Aerospace Engineering, University of Cincinnati.
    Donnelly, Lane
    Cincinnati Children's Hospital.
    Kalra, Maninder
    Cincinnati Children's Hospital.
    Computational Modeling of Upper Airway Before and After Adenotonsillectomy for Obstructive Sleep Apnea2008In: The Laryngoscope, ISSN 0023-852X, E-ISSN 1531-4995, Vol. 118, no 2, p. 360-362Article in journal (Refereed)
    Abstract [en]

    Adenotonsillectomy, the first-line surgical treatment for obstructive sleep apnea (OSA) in children, is successful in only 50% of obese children. Computational fluid dynamics tools, which have been applied to differentiate OSA patients from those without OSA based on the airway flow characteristics, can be potentially used to identify patients likely to benefit from surgical intervention. We present computational modeling of the upper airway before and after adenotonsillectomy in an obese female adolescent with OSA. The subject underwent upper airway imaging on a 1.5 Tesla magnetic resonance imaging (MRI) scanner, and three-dimensional airway models were constructed using airway boundary coordinates from cross-sectional MRI scans. Our results using computational simulations indicate that, in an obese child, the resolution of OSA after adenotonsillectomy is associated with changes in flow characteristics that result in decreased pressure differentials across the airway walls and thus lower compressive forces that predispose to airway collapse. Application of such findings to an obese child seeking surgical treatment for OSA can potentially lead to selection of the surgical procedure most likely to result in OSA resolution. Effective intervention for OSA in this high-risk group will result in reduction in morbidity and the public health concerns associated with OSA.

  • 42.
    Mihaescu, Mihai
    et al.
    Aerospace Engineering, University of Cincinnati.
    Murugappan, Shanmugam
    Otolargyngology, Head and Neck Surgery, University of Cincinnati-Medical Center.
    Gutmark, Ephraim
    Aerospace Engineering, University of Cincinnati.
    Donnelly, Lane
    Khosla, Sid
    Otolaryngology, Head & Neck Surgery, University of Cincinnati-Medical Center.
    Kalra, Maninder
    Cincinnati Children's Hospital.
    Computational Fluid Dynamics Analysis of Upper Airway Reconstructed From Magnetic Resonance Imaging Data2008In: Annals of Otology, Rhinology and Laryngology, ISSN 0003-4894, E-ISSN 1943-572X, Vol. 117, no 4, p. 303-309Article in journal (Refereed)
    Abstract [en]

    Objectives: We performed flow computations on an accurate upper airway model in a patient with obstructive sleep apnea and computed the velocity, static pressure, and wall shear stress distribution in the model.

    Methods: Cartesian coordinates for airway boundaries were determined from cross-sectional magnetic resonance images, and a 3-dimensional computational model of the upper airway was constructed. Flow simulations were then performed within a FLUENT commercial software framework. Four different flow conditions were simulated during inspiration, assuming the steady-state condition. The results were analyzed from the perspectives of velocity, static pressure, and wall shear stress distribution.

    Results: We observed that the highest axial velocity was at the site of minimum cross-sectional area (retropalatal pharynx) resulting in the lowest level of wall static pressure. The highest wall shear stresses were at the same location. The pressure drop was significantly larger for higher flow rates than for lower flow rates.

    Conclusions: Our results indicate that the presence of airway narrowing, through change in the flow characteristics that result in increased flow velocity and reduced static pressure, can itself increase airway collapsibility. Additionally, the effects of wall shear stress on airway walls may be an important factor in the progression over time of the severity of obstructive sleep apnea.

  • 43.
    Mihaescu, Mihai
    et al.
    Aerospace Engineering, University of Cincinnati.
    Murugappan, Shanmugam
    Otolargyngology, Head and Neck Surgery, University of Cincinnati-Medical Center.
    Gutmark, Ephraim
    Aerospace Engineering, University of Cincinnati.
    Elluru, Ravindhra
    Cincinnati Children's Hospital.
    Cohen, Aliza
    Cincinnati Children's Hospital.
    Willging, J. Paul
    Cincinnati Children's Hospital.
    Modeling Flow in a Compromised Pediatric Airway Breathing Air and Heliox2008In: The Laryngoscope, ISSN 0023-852X, E-ISSN 1531-4995, Vol. 118, no 12, p. 2205-2211Article in journal (Refereed)
    Abstract [en]

    Objectives/Hypothesis: The aim of this study was to perform computer simulations of flow within an accurate model of a pediatric airway with subglottic stenosis. It is believed that the airflow characteristics in a stenotic airway are strongly related to the sensation of dyspnea. Methodology: Computed tomography images through the respiratory tract of an infant with subglottic stenosis, were used to construct the three-dimensional geometry of the airway. By using computational fluid dynamics (CFD) modeling to capture airway flow patterns during inspiration and expiration, we obtained information pertaining to flow velocity, static airway wall pressure, pressure drop across the stenosis, and wall shear stress. These simulations were performed with both air and heliox. Results: Unlike air, heliox maintained laminar flow through the stenosis. The calculated pressure drop over stenosis was lower for the heliox flow, in contrast to the airflow case. This lead to an approximately 40% decrease in airway resistance when using heliox, and presumably causes a decrease in the level of effort required for breathing. Conclusions: CFD simulations offer a quantitative method of evaluating airway flow dynamics in patients with airway abnormalities. CFD modeling illustrated the flow features and quantified flow parameters within a pediatric airway with subglottic stenosis. Simulations with air and heliox conditions mirrored the known clinical benefits of heliox as compared with air. We anticipate that computer simulation models will ultimately allow a better understanding of changes in flow caused by specific medical and surgical interventions in patients with conditions associated with dyspnea.

  • 44.
    Mihaescu, Mihai
    et al.
    Aerospace Engineering, University of Cincinnati.
    Murugappan, Shanmugam
    Otolargyngology, Head and Neck Surgery, University of Cincinnati-Medical Center.
    Kalra, Maninder
    Cincinnati Children's Hospital.
    Khosla, Sid
    Otolaryngology, Head & Neck Surgery, University of Cincinnati-Medical Center.
    Gutmark, Ephraim
    Aerospace Engineering, University of Cincinnati.
    Large Eddy Simulation and Reynolds-Averaged Navier–Stokes modeling of flow in a realistic pharyngeal airway model: An investigation of obstructive sleep apnea2008In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 41, no 10, p. 2279-2288Article in journal (Refereed)
    Abstract [en]

    Computational fluid dynamics techniques employing primarily steady Reynolds-Averaged Navier–Stokes (RANS) methodology have been recently used to characterize the transitional/turbulent flow field in human airways. The use of RANS implies that flow phenomena are averaged over time, the flow dynamics not being captured. Further, RANS uses two-equation turbulence models that are not adequate for predicting anisotropic flows, flows with high streamline curvature, or flows where separation occurs. A more accurate approach for such flow situations that occur in the human airway is Large Eddy Simulation (LES). The paper considers flow modeling in a pharyngeal airway model reconstructed from cross-sectional magnetic resonance scans of a patient with obstructive sleep apnea. The airway model is characterized by a maximum narrowing at the site of retropalatal pharynx. Two flow-modeling strategies are employed: steady RANS and the LES approach. In the RANS modeling framework both k–ε and k–ω turbulence models are used. The paper discusses the differences between the airflow characteristics obtained from the RANS and LES calculations. The largest discrepancies were found in the axial velocity distributions downstream of the minimum cross-sectional area. This region is characterized by flow separation and large radial velocity gradients across the developed shear layers. The largest difference in static pressure distributions on the airway walls was found between the LES and the k–ε data at the site of maximum narrowing in the retropalatal pharynx.

  • 45.
    Mihaescu, Mihai
    et al.
    Aerospace Engineering, University of Cincinnati.
    Mylavarapu, Goutham
    Aerospace Engineering, University of Cincinnati.
    Gutmark, Ephraim
    Aerospace Engineering, University of Cincinnati.
    Powell, Nelson
    Stanford University School of Medicine.
    Large Eddy Simulation of the pharyngeal airflow associated with Obstructive Sleep Apnea Syndrome at pre and post-surgical treatment2011In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 44, no 12, p. 2221-2228Article in journal (Refereed)
    Abstract [en]

    Obstructive Sleep Apnea Syndrome (OSAS) is the most common sleep-disordered breathing medical condition and a potentially life-threatening affliction. Not all the surgical or non-surgical OSAS therapies are successful for each patient, also in part because the primary factors involved in the etiology of this disorder are not completely understood. Thus, there is a need for improving both diagnostic and treatment modalities associated with OSAS. A verified and validated (in terms of mean velocity and pressure fields) Large Eddy Simulation approach is used to characterize the abnormal pharyngeal airflow associated with severe OSAS and its interaction with the airway wall in a subject who underwent surgical treatment. The analysis of the unsteady flow at pre- and post-treatment is used to illustrate the airflow dynamics in the airway associated with OSAS and to reveal as well, the changes in the flow variables after the treatment. At pre-treatment, large airflow velocity and wall shear stress values were found at the obstruction site in all cases. Downstream of obstruction, flow separation generated flow recirculation regions and enhanced the turbulence production in the jet-like shear layers. The interaction between the generated vortical structures and the pharyngeal airway wall induced large fluctuations in the pressure forces acting on the pharyngeal wall. After the surgery, the flow field instabilities vanished and both airway resistance and wall shear stress values were significantly reduced.

  • 46.
    Mihaescu, Mihai
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Semlitsch, Bernhard
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Gutmark, Ephraim
    Aerospace Engineering, University of Cincinnati.
    Airframe Installation Effects on the Jet exhausting a Coaxial Nozzle System of a Gas Turbine Engine2012In: ASME Turbo Expo 2012 (GT2012), ASME Press, 2012, p. 347-355Conference paper (Refereed)
    Abstract [en]

    Jet engine installation effects can significantly affect the behavior of the exhausting flow otherwise axisymmetric for an axial-symmetric nozzle configuration. Considering the problem associated solely with the turbulent jet (i.e. neglecting jet interaction with the airframe or the flight effects) has severe limitations on accurately predicting the real case scenario. It should also be emphasized that the major sources of noise for an aircraft are the high velocity, turbulent hot jets exhausting aircraft’s gas turbine engines. Therefore, the prediction of the compressible jet by including wing and pylon effects represents today a topic of high interest in aeroacoustics.

    A numerical study is carried out for analyzing the flow associated with a separate flow nozzle system with and without installation effects. The Baseline case (without airframe installation) is compared with the case in which only the pylon is considered and with the case where the wing and the pylon are interfering with the jet engine. The simulations are performed with and without forward-flight effects. The tertiary flow increases the length of the potential core region while limiting the radial spread of the jet. The airframe installation effects increase the jet spreading underneath the pylon-nozzle-wing assembly while lowering the production of turbulence in that region. Particle Imaging Velocimetry experimental flow data are used to validate the computational results for the Baseline and the Pylon cases without the forward-flight effects.

  • 47.
    Mihaescu, Mihai
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Semlitsch, Bernhard
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Gutmark, Ephraim
    University of Cincinnati.
    Assessment of Turbulence Models for Predicting Coaxial Jets relevant to Turbofan Engines2012In: Conference on Modelling Fluid Flow (CMFF'12) / [ed] Janos Vad, 2012, p. 716-723Conference paper (Refereed)
    Abstract [en]

    A numerical study is carried out for analyzing the compressible, non-isothermal flow associated with a separate-flow exhaust nozzle system with conic plug. Within the steady-state Reynolds Averaged Navier-Stokes (RANS) framework, several two-equation turbulence models among which the standard k-epsilon, the standard k-omega, and two different Shear Stress Transport (SST) k-omega formulations are evaluated. In addition, Large Eddy Simulation (LES) approach is employed for capturing the flow dynamics associated with the coaxial jet. The computational results are compared against available experimental Particle Imaging Velocimetry (PIV) flow data, in terms of time-averaged axial velocity and turbulent kinetic energy levels.

  • 48.
    Mihaescu, Mihai
    et al.
    Energy Sciences, Lund University.
    Szasz, Robert
    Energy Sciences, Lund University.
    Fuchs, Laszlo
    Energy Sciences, Lund University.
    Noise Computation of a Turbo-Engine Jet Exhaust Based on LES and Lighthill's Acoustic Analogy2004In: Volume 5: Turbo Expo 2004, Parts A and B, ASME , 2004, p. 1723-1731Conference paper (Refereed)
    Abstract [en]

    Increasing noise regulations at urban airports force jet engine manufactures to develop and build more quiet engines. Over recent years, a significant reduction in fan and mechanical noise has been achieved. However, the jet exhaust is the principal source of noise. The acoustical field that is generated by a turbo-engine jet exhaust running near the ground level is considered. The full equations of motion for compressible and unsteady flows describe both flow field and sound generation. The flow variables are decomposed into semi-compressible components and inviscid, irrotational acoustical components. The turbulent flow and mixing are computed using Large Eddy Simulation (LES). The radiated acoustical field is computed using the Lighthill's acoustic analogy with acoustic sources provided by instantaneous LES data.

  • 49.
    Mihaescu, Mihai
    et al.
    Energy Sciences, Lund University.
    Szasz, Robert
    Energy Sciences, Lund University.
    Fuchs, Laszlo
    Energy Sciences, Lund University.
    Gutmark, Ephraim
    Aerospace Engineering, University of Cincinnati.
    Coaxial Jet Noise Prediction: Grid Resolution Effect on the Numerical Solution2005In: Collection of Technical Papers - 11th AIAA/CEAS Aeroacoustics Conference, AIAA , 2005, p. 3586-3595Conference paper (Refereed)
    Abstract [en]

    The flow and acoustic fields that are generated by two coaxial jets are considered. The problem is handled by solving the flow field using Large Eddy Simulation (LES) and the acoustics by a wave equation with source terms provided by the instantaneous LES. The paper is focused on the influence of the grid resolution on the solution accuracy.

  • 50.
    Mihaescu, Mihai
    et al.
    Energy Sciences, Lund University.
    Szasz, Robert
    Energy Sciences, Lund University.
    Fuchs, Laszlo
    Energy Sciences, Lund University.
    Gutmark, Ephraim
    Aerospace Engineering, University of Cincinnati.
    Flow and Noise Investigations of a Separate Flow Exhaust System2005In: Proceedings of the ASME Turbo Expo 2005, Vol 6, Pts A and B, ASME , 2005, p. 1221-1229Conference paper (Refereed)
    Abstract [en]

    A major component of aircraft noise is the jet noise created by the high velocity hot stream exhausting from a jet engine, interacting with itself and with the surrounding cold air. In the present paper the flow and acoustic fields that are generated by two coaxial jets are considered. Numerically, the problem is divided into a flow related part (Navier-Stokes system of equation) and an acoustic part (an inhomogeneous wave equation). The flow field is handled by well resolved Large Eddy Simulation (LES). The acoustical sources can then be computed from the flow field calculations, on the near-field "source" grid. The acoustic field is solved, on the same or even on a larger separate grid, by using an acoustic approximation with appropriate acoustic boundary conditions. The computed flow and acoustical fields are compared to those measured on the separate flow nozzle test facility. The comparisons in terms of velocity and sound pressure levels are shown to validate the used approach. Frequency spectra of the acoustic density fluctuation are presented in order to indicate the locations where the high- or low- frequency noise dominates. The numerical study is focused as well on the Reynolds number effects on the flow and acoustics.

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