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  • 1.
    Hynninen, Antti
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. VTT Technical Research Centre of Finland Ltd.
    Acoustic In-duct Characterization of Fluid Machines with Applications to Medium Speed IC-engines2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The unwanted sound, noise, can lead to health problems, e.g. hearing loss and stress-related problems. A pre-knowledge of noise generation by machines is of great importance due to the ever-shorter product development cycles and stricter noise legislation. The noise from a machine radiates to the environment indirectly via the foundation structure and directly via the surrounding fluid. A fluid machine converts the energy from the fluid into mechanical energy or vice versa. Examples of the fluid machines are internal combustion engines (IC-engines), pumps, compressors, and fans. Predicting and controlling noise from a fluid machine requires a model of the noise sources themselves, i.e. acoustic source data. In the duct systems connected to the fluid machines, the acoustic source interacts strongly with the system boundaries, and the source characteristics must be described using in-duct methods.

    Above a certain frequency, i.e. first non-plane wave mode cut-on frequency, the sound pressure varies over the duct cross-section and non-plane waves are introduced. For a number of applications, the plane wave range dominates and the non-plane waves can be neglected. But for machines connected to large ducts, the non-plane wave range is also important. In the plane wave range, one-dimensional process simulation software can be used to predict, e.g. for IC-engines, the acoustic in-duct source characteristics. The high frequency phenomena with non-plane waves are so complicated, however, that it is practically impossible to simulate them accurately. Thus, in order to develop methods to estimate the sound produced, experimental studies are also essential.

    This thesis investigates the acoustic in-duct source characterization of fluid machines with applications to exhaust noise from medium speed IC-engines.  This corresponds to large engines used for power plants or on ships, for which the non-plane wave range also becomes important. The plane wave source characterization methods are extended into the higher frequency range with non-plane waves. In addition, methods to determine non-plane wave range damping for typical elements in exhaust systems, e.g. after-treatment devices, are discussed.

  • 2.
    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.

  • 3.
    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.
    Åbom, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
    Acoustic Simulation of Medium Speed IC-Engine Exhaust Gas After Treatment Devices with Substrate2014Other (Refereed)
    Abstract [en]

    The after treatment devices (ATD) used in internal combustion engine (IC-engine) exhaust systems are mainly designed with emphasis on emission control, i.e. chemical efficiency, while paying less attention to the acoustic performance. In automotive applications, the duct diameters are so small that studying the acoustic wave propagation only in the plane wave frequency range is usually sufficient. In the case of medium speed IC-engines, used for example in power plants and ships, the three dimensional acoustic phenomena must also be taken into account. The main elements of the medium speed IC-engine ATD are the selective catalytic reducer (SCR) and oxidation catalyst (OC), which are based on a large amount of coated channels, i.e. the substrates. The number and type of the substrates depends not only on the regional environment legislations but also on the engine type. In this study the acoustic attenuation of a medium speed IC-engine ATD is simulated and the results are compared with measurements. The focus is in the low and mid frequency range. That is, the three dimensional waves inside the ATD are taken into account whereas only the plane waves are assumed to propagate at the inlet and outlet ports. The paper also discusses how to extend the classical one dimensional two-port solution into the higher frequencies. Using the computationally effective two-port solution in a wider frequency range is of great importance, e.g., when searching the acoustically optimal substrate configuration.

  • 4. 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.

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