| 1. |
- Fares, Omar, 1992, et al.
(författare)
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Numerical Investigation of Narrow-Band Noise Generation by Automotive Cooling Fans
- 2020
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627.
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Tidskriftsartikel (refereegranskat)abstract
- Axial cooling fans are commonly used in electric vehicles to cool batteries with high heating load. One drawback of the cooling fans is the high aeroacoustic noise level resulting from the fan blades and the obstacles facing the airflow. To create a comfortable cabin environment in the vehicle, and to reduce exterior noise emission, a low-noise installation design of the axial fan is required. The purpose of the project is to develop an efficient computational aeroacoustics (CAA) simulation process to assist the cooling-fan installation design. This paper reports the current progress of the development, where the narrow-band components of the fan noise is focused on. Two methods are used to compute the noise source. In the first method the source is computed from the flow field obtained using the unsteady Reynolds-averaged Navier-Stokes equations (unsteady RANS, or URANS) model. In the second method, the azimuthal modes of the flow field obtained using the steady RANS with the moving reference frame model are treated as the sound source. While the first method is able to resolve any narrow-band noise source that is related to large-scale harmonic oscillations, the second method may only be able to estimate the sound source at the blade passing frequency and its harmonics. The acoustic field generated by the sound source is computed by solving the inhomogeneous Helmholtz equation. The simulation process based on both methods is applied to a benchmark case in the literature and the simulated results are compared with experimental data. Satisfactory agreement is observed from the comparison.
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| 2. |
- Futrzynski, Romain, 1988-, et al.
(författare)
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Numerical study of the Stokes layer in oscillating channel flow
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Oscillating turbulent channel flows present particular physics that proves to be particularly difficult to understand. In this paper, a case where the amplitude of the oscillations at the center of the channel is approximately 15% of the mean velocity and the dimensionless angular forcing frequency is 0.01 was studied using several numerical methods. DNS was performed to serve as reference to which the results from an LES were compared. The LES data was post-processed using both phase averaging and the more recent dynamic mode decomposition (DMD), which extracts coherent structures based on their frequency. It was found that the DMD is not able to extract faint harmonic components of the oscillations, which have been observed with phase averaging and Fourier transforms. It is, however, able to extract accurate profiles of the mean and forcing frequency quantities. Compared to the DNS, the accuracy of the LES results was similar to analytical models, although no single model gives accurate result for every quantity investigated.
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| 3. |
- Holmberg, Andreas, et al.
(författare)
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A frequency domain linearized Navier-Stokes method including acoustic damping by eddy viscosity using RANS
- 2015
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 346, s. 229-247
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, a method for including damping of acoustic energy in regions of strong turbulence is derived for a linearized Navier-Stokes method in the frequency domain. The proposed method is validated and analyzed in 2D only, although the formulation is fully presented in 3D. The result is applied in a study of the linear interaction between the acoustic and the hydrodynamic held in a 2D T-junction, subject to grazing flow at Mach 0.1. Part of the acoustic energy at the upstream edge of the junction is shed as harmonically oscillating disturbances, which are conveyed across the shear layer over the junction, where they interact with the acoustic field. As the acoustic waves travel in regions of strong shear, there is a need to include the interaction between the background turbulence and the acoustic field. For this purpose, the oscillation of the background turbulence Reynolds stress, due to the acoustic Field, is modeled using an eddy Newtonian model assumption. The time averaged flow is first solved for using RANS along with a k-epsilon turbulence model. The spatially varying turbulent eddy viscosity is then added to the spatially invariant kinematic viscosity in the acoustic set of equations. The response of the 2D T-junction to an incident acoustic field is analyzed via a plane wave scattering matrix model, and the result is compared to experimental data for a T-junction of rectangular ducts. A strong improvement in the agreement between calculation and experimental data is found when the modification proposed in this paper is implemented. Discrepancies remaining are likely due to inaccuracies in the selected turbulence model, which is known to produce large errors e.g. for flows with significant rotation, which the grazing flow across the T-junction certainly is A natural next step is therefore to test the proposed methodology together with more sophisticated turbulence models.
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| 4. |
- Holmberg, Andreas, et al.
(författare)
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A linearized Navier-Stokes method including turbulence damping
- 2013
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Ingår i: 19th AIAA/CEAS Aeroacoustics Conference. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624102134
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Konferensbidrag (refereegranskat)abstract
- In this paper, a method for including damping of acoustic energy in regions of strong turbulence is derived for a linearized Navier-Stokes method in the frequency domain. The result is applied in a study of the linear interaction of the acoustic and the hydrodynamic field in a 2D T-junction, subject to grazing flow at Mach 0.1. As the acoustic waves travel in regions of strong shear, there is a need to include the interaction between the background turbulence and the acoustic field. For this purpose, the oscillation of the background turbulence Reynold's stress, due to the acoustic field, is modeled using an eddy Newtonian model assumption. The time averaged flow is first solved for using RANS along with a k-ε turbulence model. The spatially varying turbulent viscosity is then added to the spatially invariant kinematic viscosity in the acoustic set of equations. The response of the 2D T-junction to an incident acoustic field is analyzed via a plane wave scattering matrix model, and the result is compared to experimental data for a T-junction of rectangular ducts. A strong improvement in the agreement between calculation and experimental data is found when the modification proposed in this paper is implemented.
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| 5. |
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| 6. |
- Karlsson, Mikael, et al.
(författare)
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Prediction of the onset of sound amplification at shear layers using linear stability analysis
- 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 simple numerical technique for predicting the potentiality of sound amplification by shear layers is presented. The technique applies Howe’s energy corollary to describe the energy exchange between the vortical mode in the shear layer and the acoustic wave incident on the layer. Potential sound amplification by the vortical mode is identified when the net energy gain of the incident acoustic wave is positive. The technique only requires steady flow simulation and linear stability analysis so the computational cost is modest. Numerical results are compared with a measurement on a particle agglomeration pipe and it shows that the sound amplification can be satisfactorily predicted by the simple technique.
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| 7. |
- Pietroniro, Asuka Gabriele, et al.
(författare)
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Propagation and Reflection Properties of Computational Setups for Radial Compressor Direct Noise Computation
- 2020
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Ingår i: Forum Acusticum.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In compressor noise simulations that are run without acoustic analogies, the direct noise computation (DNC) approach is utilised, allowing the acoustic waves to be solved in the time domain. The intent of the present paper is to analyse the effects of several solver and grid settings on the propagation of acoustic waves through the domain and on their reflection from the boundaries. Such effects are addressed and quantified in the present analysis, which is conducted on cylindrical pipes used as inlets in turbocharger compressor setups.The results show that reflection coefficients below 1% can be achieved, and that non-linear effects may exert an influence on the propagated waves’ amplitudes and decay rates.Together with the wave decomposition approach chosen, the analyses run make the present work a solid base from which to run trust worthy direct noise computation and accurate post-processing.
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| 8. |
- Pietroniro, Asuka Gabriele
(författare)
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Turbocharger Compressor Noise: a Numerical Study
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Road transport is the primary means of conveyance of passengers and freight in the EU, accounting for 71% and 52% of the totals, respectively. At low speeds and in situations with frequent start-stops and accelerations, i.e., typical in downtowns and residential areas, the noise from the turbocharger compressor becomes a distinctive source of noise and an important contributor to road transport noise, affecting human health and wildlife, both inside and outside urban areas. To reach quieter operation, the reduction of the aerodynamic noise sources must be addressed; by investigating the noise mechanisms, it is possible to develop noise reduction technologies.The thesis' aim is to be a systematic numerical study of the aerodynamically generated noise in turbocharger compressors. Several simulation techniques were employed in the search for a thorough understanding of the acoustic behaviour of such machines, spanning from the steady state Reynolds averaged Navier Stokes (RANS) with a quick turnaround to the scale-resolving detached eddy simulation (DES), allowing to retrieve information about the acoustic field by means of turbulence predictions and the direct noise computation (DNC) approach. The acoustic results, only describing source information thanks to the non-reflecting boundary conditions developed as part of the work, were verified against experimental data with satisfactory match. On data from such setups, decomposition techniques based on the momentum potential theory (MPT) and the dynamic mode decomposition (DMD) were implemented to gain further insight into the noise generation mechanisms and the locations of the fluctuations of main interest.The study is a valuable base on which to develop further aerodynamic noise source investigations within rotating machines.
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| 9. |
- Weng, Chenyang, et al.
(författare)
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Direct numerical simulation of coherent perturbations in a low mach number turbulent channel flow
- 2014
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Ingår i: 21st International Congress on Sound and Vibration 2014, ICSV 2014. - 9781634392389 ; , s. 2019-2026
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Konferensbidrag (refereegranskat)abstract
- When acoustic wave propagates in turbulent flows, the modulated turbulent stresses can cause wave attenuation. Recently the present authors proposed a non-equilibrium model to determine the effective turbulent stress acting on the acoustic wave in duct flows, which can be used to predict the wave attenuation caused by turbulent mixing. The model reveals that the modulated turbulent stress and the wave shear strain rate near the wall are out of phase for a certain range of the Strouhal number. In this paper, direct numerical simulation (DNS) of small coherent perturbations in turbulent channel flow is performed to validate the model. The simulation results confirms the predictions by the proposed model.
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| 10. |
- Weng, Chenyang
(författare)
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Modeling of sound-turbulence interaction in low-Mach-number duct flows
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- When sound waves propagate in a duct in the presence of turbulent flow, tur- bulent mixing can cause extra attenuation of the sound waves in addition to that caused by the viscothermal eects. Experiments show that compared to the vis- cothermal eects, turbulent absorption becomes the dominant contribution to the sound attenuation at suciently low frequencies. The mechanism of this turbulent absorption is attributed to the turbulent stress and the turbulent heat transfer act- ing on the coherent perturbations (including to sound waves) near the duct wall, i.e. sound-turbulence interaction.The purpose of the current investigation is to understand the mechanism of the sound-turbulence interaction in low-Mach-number internal flows by means of theoretical modeling and numerical simulation. The turbulence absorption can be modeled through perturbation turbulent Reynolds stresses and perturbation turbu- lent heat flux in the linearized perturbation equations. In this thesis, the linearized perturbation equations are reviewed, and dierent models for the turbulent absorp- tion of the sound waves are investigated. In addition, a new non-equilibrium model for the perturbation turbulent Reynolds stress is proposed. The proposed model is validated by comparing the computed perturbation fields with experimental data from turbulent pipe flow measurements, and large eddy simulations (LES) of turbu- lent channel flow. Good agreements are observed.Besides the theoretical modeling, LES is also carried out as a numerical investi- gation of the sound-turbulence interaction. Some preliminary results from the LES are presented.
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| 11. |
- Weng, Chenyang, et al.
(författare)
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Numerical and theoretical investigation of pulsatile turbulent channel flows
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The turbulent channel flow subjected to imposed harmonic oscillations is studied by theo- retical models and direct numerical simulations (DNS). A linear model proposed earlier by the present authors for the coherent perturbation Reynolds shear stress is reviewed and discussed in depth. The model includes the non-equilibrium effects during the response of the Reynolds stress to the imposed periodic shear straining, where a phase lag exists between the stress and the strain. To validate the model, the DNS results are compared with the perturbation velocity and Reynolds shear stress computed from the model. The performance of the model is good in the frequency range where quasi-static assumptions are invalid, and the viscoelastic characteris- tics of the turbulent eddies implied by the model is supported by the DNS. Attempts to improve the model are also made by incorporating in the model the DNS data. In addition, the onset of the nonlinear effects during the production of the perturbation Reynolds stresses are discussed based on the DNS data, new physical features observed from the DNS are reported.
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| 12. |
- Weng, Chenyang, et al.
(författare)
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Numerical and theoretical investigation of pulsatile turbulent channel flows
- 2016
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Ingår i: Journal of Fluid Mechanics. - : Cambridge University Press. - 0022-1120 .- 1469-7645. ; 792, s. 98-133
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Tidskriftsartikel (refereegranskat)abstract
- A turbulent channel flow subjected to imposed harmonic oscillations is studied by direct numerical simulation (DNS) and theoretical models. Simulations have been performed for different pulsation frequencies. The time- and phase-averaged data have been used to analyse the flow. The onset of nonlinear effects during the production of the perturbation Reynolds stresses is discussed based on the DNS data, and new physical features observed in the DNS are reported. A linear model proposed earlier by the present authors for the coherent perturbation Reynolds shear stress is reviewed and discussed in depth. The model includes the non-equilibrium effects during the response of the Reynolds stress to the imposed periodic shear straining, where a phase lag exists between the stress and the strain. To validate the model, the perturbation velocity and Reynolds shear stress from the model are compared with the DNS data. The performance of the model is found to be good in the frequency range where quasi-static assumptions are invalid. The viscoelastic characteristics of the turbulent eddies implied by the model are supported by the DNS data. Attempts to improve the model are also made by incorporating the DNS data in the model.
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| 13. |
- Weng, Chenyang, et al.
(författare)
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On the calculation of the complex wavenumber of plane waves in rigid-walled low-Mach-number turbulent pipe flows
- 2015
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 354, s. 132-153
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Tidskriftsartikel (refereegranskat)abstract
- A numerical method for calculating the wavenumbers of axisymmetric plane waves in rigid walled low-Mach-number turbulent flows is proposed, which is based on solving the linearized Navier-Stokes equations with an eddy viscosity model. In addition, theoretical models for the wavenurnbers are reviewed, and the main effects (the viscothermal effects, the mean flow convection and refraction effects, the turbulent absorption, and the moderate compressibility effects) which may influence the sound propagation are discussed. Compared to the theoretical models, the proposed numerical method has the advantage of potentially including more effects in the computed wavenurnbers.The numerical results of the vvavenumbers are compared with the reviewed theoretical models, as well as experimental data from the literature. It shows that the proposed numerical method can give satisfactory prediction of both the real part (phase shift) and the imaginary part (attenuation) of the measured wavenumbers, especially when the refraction effects or the turbulent absorption effects become important.
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| 14. |
- Weng, Chenyang, et al.
(författare)
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Sound-turbulence interaction in low Mach number duct flow
- 2013
-
Ingår i: 19th AIAA/CEAS Aeroacoustics Conference. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624102134
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- When sound waves propagate in ducts with the presence of turbulent flow, turbulent stresses can cause extra attenuation of the wave in addition to that caused by viscothermal effects. Different models for the turbulent stress acting on the sound waves are investigated in this study, and they are applied to compute the wall shear stress impedance of sound waves. Among these models the non-equilibrium model proposed by the present authors in another paper is studied in details. Attempt of including mean flow convection effect in the non-equilibrium model is made. The resulting modified model is then applied to compute the wave attenuation, and the results are compared with experimental data.
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| 15. |
- Weng, Chenyang, et al.
(författare)
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The attenuation of sound by turbulence in internal flows
- 2013
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Ingår i: Journal of the Acoustical Society of America. - USA : Acoustical Society of America (ASA). - 0001-4966 .- 1520-8524. ; 133:6, s. 3764-3776
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Tidskriftsartikel (refereegranskat)abstract
- The attenuation of sound waves due to interaction with low Mach number turbulent boundary layers in internal flows (channel or pipe flow) is examined. Dynamic equations for the turbulent Reynolds stress on the sound wave are derived, and the analytical solution to the equation provides a frequency dependent eddy viscosity model. This model is used to predict the attenuation of sound propagating in fully developed turbulent pipe flow. The predictions are shown to compare well with the experimental data. The proposed dynamic equation shows that the turbulence behaves like a viscoelastic fluid in the interaction process, and that the ratio of turbulent relaxation time near the wall and the sound wave period is the parameter that controls the characteristics of the attenuation induced by the turbulent flow.
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| 16. |
- Weng, Chenyang, 1985-
(författare)
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Theoretical and numerical studies of sound propagation in low-Mach-number duct flows
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- When sound waves propagate in a duct in the presence of turbulent flow, turbulent mixing can cause attenuation of the sound waves extra to that caused by the viscothermal effects. Experiments show that compared to the viscothermal effects, this turbulent absorption becomes the dominant contribution to the sound attenuation at sufficiently low frequencies. The mechanism of this turbulent absorption is attributed to the turbulent stress and the turbulent heat transfer acting on the coherent perturbations (including the sound waves) near the duct wall, i.e. sound-turbulence interaction.The purpose of the current investigation is to understand the mechanism of the sound-turbulence interaction in low-Mach-number internal flows by theoretical modeling and numerical simulations. The turbulence absorption can be modeled through perturbation turbulent Reynolds stresses and perturbation turbulent heat flux in the linearized perturbation equations. In this thesis, the linearized perturbation equations are reviewed, and different models for the turbulent absorption of the sound waves are investigated. A new non–equilibrium model for the perturbation turbulent Reynolds stress is also proposed. The proposed model is validated by comparing with experimental data from the literature, and with the data from Direct Numerical Simulations (DNS) of pulsating turbulent channel flow. Good agreement is observed.
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