| 1. |
- Knutsson, Magnus, et al.
(författare)
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The effect of turbulence damping on acoustic wave propagation in tubes
- 2010
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 329:22, s. 4719-4739
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Tidskriftsartikel (refereegranskat)abstract
- The attenuation of sound due to the interaction between a low Mach number turbulent boundary layer and acoustic waves can be significant at low frequencies or in narrow tubes. In a recent publication by the present authors the acoustics of charge air coolers for passenger cars has been identified as an interesting application where turbulence attenuation can be of importance. Favourable low-frequency damping has been observed that could be used for control of the in-duct sound that is created by the engine gas exchange process. Analytical frequency-dependent models for the eddy viscosity that controls the momentum and thermal boundary layers are available but are restricted to thin acoustic boundary layers. For cases with cross-sections of a few millimetres a model based on thin acoustic boundary layers will not be applicable in the frequency range of interest. In the present paper a frequency-dependent axis-symmetric numerical model for interaction between turbulence and acoustic waves is proposed. A finite element scheme is used to formulate the time harmonic linearized convective equations for conservation of mass, momentum and energy into one coupled system of equations. The turbulence is introduced with a linear model for the eddy viscosity that is added to the shear viscosity. The proposed model is validated by comparison with experimental data from the literature.
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| 2. |
- Tiikoja, H., et al.
(författare)
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Investigations of automotive turbocharger acoustics
- 2011
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Ingår i: SAE technical paper series. - : SAE International. - 0148-7191. ; 4:2, s. 2531-2542
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Tidskriftsartikel (refereegranskat)abstract
- In this paper an overview of recent experimental studies performed at KTH on the sound transmission and sound generation in turbochargers is presented. The compressor and turbine of the turbochargers are treated as acoustic active 2-ports and characterized using the unique experimental test facility established at KTH. The 2-port model is limited to the plane wave range so for higher frequencies the propagating acoustic power is estimated using an average based on pressure cross-spectra. A number of automotive turbochargers have been studied for a variety of operating conditions systematically selected from the compressor and turbine charts. The paper discusses the experimental procedures including special techniques implemented to improve the quality of the data. Results from a number of experiments on various modern automotive turbochargers including a unit with variable turbine geometry (VTG) are presented. Copyright
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| 3. |
- Farooqui, Maaz, et al.
(författare)
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Measurement of perforate impedance with grazing flow on both sides
- 2016
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Ingår i: 22nd AIAA/CEAS Aeroacoustics Conference. American Institute of Aeronautics and Astronautics.. - Reston, Virginia : American Institute of Aeronautics and Astronautics.
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Konferensbidrag (refereegranskat)abstract
- In this paper, the acoustic impedance of a microperforated plate (MPP) with two-sided grazing flow is educed by a modified semi-analytical inverse technique. The MPP sample is placed in the middle of a rectangular duct with grazing flow. The mode matching formulation is derived in terms of pressure for a MPP with two-sided grazing flow. The inputs to this mode matching technique are complex acoustic pressure measured at twelve positions at the wall of the duct, upstream and downstream of the MPP section. First the ability of the code to reproduce the pressure field for a given impedance is tested. Second the ability to educe the correct impedance for a given pressure distribution is tested. The results of the mode matching code are in good agreement with the simulations for no flow cases.
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| 4. |
- Meng, Yang, et al.
(författare)
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Semi-empirical impedance model of perforated plate under grazing flow
- 2019
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Ingår i: 25th AIAA/CEAS Aeroacoustics Conference, 2019. - Reston, Virginia : American Institute of Aeronautics and Astronautics Inc, AIAA.
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Konferensbidrag (refereegranskat)abstract
- A semi-empirical impedance formula of a circular orifice under grazing flow is derived, based on a linearized potential flow model. The effect of boundary layer is considered by introducing the convection speed of vorticity which is assumed to be a function of the dimensionless boundary layer thickness. Asymptotic expression of the impedance at low Strouhal number is acquired by the method of perturbation, while the impedance at large Strouhal number can be well approximated by that without grazing flow. The model predictions achieve reasonable agreement with the data available in a previous experimental investigation.
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| 5. |
- Arteaga, Ines L., et al.
(författare)
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The TRANSIT project: innovation towards train pass-by noise source characterisation and separation tools
- 2023
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Ingår i: 2022 Conference Proceedings Transport Research Arena, TRA Lisbon 2022. - : Elsevier B.V.. ; , s. 989-996
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Konferensbidrag (refereegranskat)abstract
- In TRANSIT, experimental methods are developed to separate and characterise noise sources on moving trains. Improved microphone array techniques allow quantification of sound power and directivity. Source separation methods based on the Pass-By Analysis method, Advanced Transfer Path Analysis and the TWINS model are also developed. For trains at standstill, new test methods are developed to quantify noise transmission paths from sources to the standard microphone positions accounting for installation effects. Several measurement campaigns are used to demonstrate and verify these methods. In addition, innovative materials and methods are investigated for improved sound comfort in trains. Approaches considered include optimal sound absorption at the source, attenuation along ducts for air conditioning systems and innovative meta-structure designs for the car-body parts.
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| 6. |
- Holmberg, Andreas, 1982-, et al.
(författare)
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Aeroacoustics of rectangular T-junctions subject to combined grazing and bias flows - An experimental investigation
- 2015
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 340, s. 152-166
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Tidskriftsartikel (refereegranskat)abstract
- Scattering matrices are determined experimentally and used to study the low amplitude interaction, between the acoustic and the hydrodynamic fields in a T-junction of rectangular ducts. In particular, combinations of grazing and bias flows are investigated in the study. It is observed that for all flow combinations, waves incident on the junction at the downstream side only are attenuated, while waves incident at the other branches may be amplified or attenuated, depending on the Strouhal number. When bias in flow is introduced to a grazing flow, there is first an increase and then a decrease in both amplification and attenuation, as the bias in-flow Mach number is increased. Comparing with T-junctions of circular ducts, the interaction is stronger for rectangular duct junctions.
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| 7. |
- Jacob, Stefan, Dr. 1980-, et al.
(författare)
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Acoustic scattering in a small centrifugal compressor based on the use of linearized equations in a rotating frame
- 2023
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Ingår i: Journal of Sound and Vibration. - : Elsevier. - 0022-460X .- 1095-8568. ; 544, s. 117315-117315
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Tidskriftsartikel (refereegranskat)abstract
- Numerical solutions of acoustic wave scattering are often used to describe sound propagation through complex geometries. For cases with flow, various forms of the convected equation have been used. A better alternative that includes vortex-sound interaction is instead to use the linearized and harmonic forms of the unsteady fluid flow governing equations. In this paper, a formulation of the linearized equations that include rotational effects, in an acoustic computation using a rotating frame of reference in a stationary geometry, is presented. We demonstrate that rotational effects can be important, e.g., when computing the transmission loss through high-speed compressors. The implementation of the proposed addition to the existing schemes is both simple and numerically inexpensive. The results are expected to have an impact on the research and development related to noise control of high-performance turbo-machinery, e.g., used in automotive or aviation applications at operating conditions that can be represented by steady background flows.
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| 8. |
- Kabral, Raimo, et al.
(författare)
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Experimental acoustic characterization of automotive twin-scroll turbine
- 2017
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Ingår i: 12th European Conference on Turbomachinery Fluid Dynamics and Thermodynamics, ETC 2017. - : KTH Royal Institute of Technology.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The present paper focuses on the experimental determination of automotive twin-scroll turbine acoustic performance. The unique test-rig for automotive turbocharger acoustics at KTH CCGEx laboratory is further developed to enable testing of modern twin-scroll turbines under controlled laboratory conditions. It is shown how the passive acoustic properties of such turbines can be accurately characterized by means of an acoustic three-port formulation. Governing equations along with the new test-rig design are presented and discussed in detail. Furthermore, complementary results from the first experimental determination of twin-scroll turbine acoustic three-port data are presented.
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| 9. |
- Orrenius, Ulf, et al.
(författare)
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Rail vehicle source models within a virtual certification process
- 2020
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Ingår i: Euronoise 2015. - : DC/ConfOrg. ; , s. 2043-2048
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Konferensbidrag (refereegranskat)abstract
- In the present paper vehicle noise source modelling work carried out within the Acoutrain project is presented. When the noise source system is surrounded by many reflectors, for example a radiating transformer behind roof shrouds, a single monopole with averaged transfer function is suggested to represent the source. For a source with strong directivity placed in an essentially free space, a “box-source” method is recommended to take into account of the source directivity. The total sound power is in this case divided into five independent noise sources which are obtained via standard sound power measurement methods and certain data processing. Experimental verifications are made for several cases in laboratory and in the field. Good correlation between tests and modelling results are obtained for both approaches.
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| 10. |
- Pietroniro, Asuka Gabriele, et al.
(författare)
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HVAC Blower : A Steady State RANS Noise Prediction Method
- 2024
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Ingår i: 13th International Styrian Noise, Vibration and Harshness Congress: The European Automotive Noise Conference, SNVH 2024. - : SAE International.
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Konferensbidrag (refereegranskat)abstract
- In an ever-transforming sector such as that of private road transport, major changes in the propulsion systems entail a change in the perception of the noise sources and the annoyance they cause. As compared to the scenario encountered in vehicles equipped with an internal combustion engine (ICE), in electrically propelled vehicles the heating, ventilation, and air conditioning (HVAC) system represents a more prominent source of noise affecting a car's passenger cabin. By virtue of the quick turnaround, steady state Reynolds-averaged Navier Stokes (RANS)- based noise source models are a handy tool to predict the acoustic power generated by passenger car HVAC blowers. The study shows that the most eminent noise source type is the dipole source associated with fluctuating pressures on solid surfaces. A noise map is generated from the noise source models data, giving indications of how changes in operating conditions affect the acoustic output of the machine throughout its operating range. The capability to predict power spectra with steady state RANS is investigated, and the overall sound power level of several operating points is validated against experimental data, showing good match. The study aims at establishing steady state RANS noise source models as a valuable tool in preliminary acoustic analyses of HVAC blower designs, in particular in the early stage of new design studies, thus helping the industry to better target quieter operation and enhanced passenger comfort.
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