Buffeting Noise Research Articles

Active control of cavity buffeting noise using a dielectric barrier discharge plasma actuator

This work examines the active control of vehicle buffeting noise using a dielectric barrier discharge plasma actuator (DBD-PA). First, the buffeting noise characteristics of a cavity under different inflow wind speeds are established through a wind tunnel test, and the effectiveness of the buffeting noise measurement results is verified. Various types of actuator layouts are designed based on specific combinations of parameters, and the interval optimization algorithm is used to identify the layout type of actuators that have the best equalization control effect under different inflow wind speeds. The experimental results regarding buffeting noise characteristics show that the buffeting frequency and the peak value of the sound pressure level increase with the increasing of wind speed. The control results show that the overall control effect of the reverse layout of the span-wise DBD-PA (SDBD-PA) is better than that of the positive layout. Consequently, the control effects of the SDBD-PA layout decrease in the front, rear, and oblique directions. A DBD vortex generator (DBD-VG) has no control effect when it is arranged in the front but has a certain control effect when it is arranged in the rear. The control effect is better with longer DBD-VGs. The results of running the interval optimization algorithm at different incoming wind speeds are as follows: reverse-front-SDBD-PA and long-rear-DBD-VG can achieve the best equalization control effect of cavity buffeting noise. The average noise reduction values are 5.26 dB and 4.42 dB, respectively, and the maximum noise reduction values are 7.48 dB and 5.79 dB, respectively.

Exploring the suppression mechanism of wind buffeting noise with bionic structures featuring leading-edge serrations and surface ridges

The aim of this study is to investigate the effectiveness and mechanism of wind buffeting noise suppression using a new bionic structure inspired by the quiet flight of owls. Firstly, the new bionic schemes based on NACA0012 wing with two sinusoidal leading-edge serrations and one straight leading-edge curve are used in a cavity after verifying the simulation. Then, the results of the three bionic schemes are compared and analyzed. It is found that the schemes with leading-edge serrations and surface ridges can suppress wind buffeting noise effectively. In particular, the sinusoidal scheme with a wavelength λ = 0.24 c (chord length c) can significantly reduce resonance energies above 21 dB over a wide range of speeds. Furthermore, the study reveals that in the bionic scheme, only the negative pressure core moves in the opening and hits the trailing edge, which reduces the pressure fluctuation in the cavity. The boundary layer thickness (BLT) also fluctuates in span under the influence of the leading-edge serration and the surface ridge, which is favorable for suppressing wind buffeting noise. However, the suppression effect is not solely related to the fluctuation of BLT in the span at the trailing edge but is also influenced by the minimum BLT at this point. Therefore, if the BLT has a certain intensity fluctuation in the span, and the minimum BLT at the trailing edge is close to that of the smooth airfoil scheme, the noise suppression effect is significant.

Energy transfer characteristics of sunroof wind buffeting noise via dynamic mode decomposition

To further investigate the reason contributing to the abrupt increase in pressure fluctuations on the sunroof and the characteristics of energy transfer between velocity and pressure, dynamic mode decomposition (DMD) is performed to investigate the dynamic characteristics of related coherent structures on the sunroof. First, a large eddy simulation is applied to a sports utility vehicle with a fully open sunroof, and the simulation results are verified via wind tunnel tests. Subsequently, the steady-state and transient characteristics of the flow field are investigated. The significant pressure fluctuation in the passenger compartment is discovered to be related to the pressure core at the trailing edge; however, the significant amount of energy exhibited by the pressure core at the trailing edge remains unclear. In addition, important information that explains the significant pressure fluctuations is obfuscated by the relatively random fluctuations in the turbulence. Thus, DMD is performed to extract the main coherent structures, including the fluctuating pressure and velocity. Finally, the relationships among the fluctuating pressure, fluctuating velocity, and their energy properties are investigated simultaneously. The results show that DMD is excellent for extracting the dominant coherent structures. A comparison between the model results for the fluctuating pressure and velocity at f = 15.0 Hz shows that the fluctuating pressure in the passenger compartment is primarily related to the positive and negative fluctuating pressure cores near the trailing edge. The significant pressure fluctuations between the center and trailing edge of the sunroof are caused by the vortices expanding and pushing against each other. In addition, the self-sustained oscillation in the sunroof is caused by the vortex extruded from the trailing edge, which causes the new vortex at the leading edge to collapse rapidly.

Wind-buffeting noise characteristics of simple cavity model based on nonlinear LRN/DES turbulence model

In this article, a nonlinear LRN/DES turbulence model is proposed by introducing nonlinear Reynolds stress and scale resolution simulation methods to address the contradiction between computational cost and accuracy of existing turbulence models in wind buffeting noise simulations. After verifying the feasibility of the model by backward-facing step flow, wind buffeting noise simulation is carried out based on the simple cavity model. By comparing with several turbulence models commonly used in wind buffeting noise simulation and experimental results, it is found that the nonlinear LRN/DES model simulates the frequency and sound pressure level of wind buffeting noise of the simple cavity model most accurately, and the capture of the flow field is also closest to the experimental result.

Numerical Analysis and Optimization of the Front Window Visor for Vehicle Wind Buffeting Noise Reduction Based on Zonal SAS k-ε Method

Numerical investigations were conducted to determine the effectiveness of the front window visor for wind buffeting noise reduction. An unsteady flow simulation was carried out using a zonal Scale Adaptive Simulation (SAS) k-ε turbulence model. Firstly, the accuracy of the simulation method was validated based on a benchmark problem. The benchmark results, frequency, and sound pressure levels of feedback and resonance modes all matched well with the experimental data. The effect of the front window on the buffeting noise reduction was numerically investigated based on three different front side window openings. The analysis focused on the suppression effect of the front window visor. The results show that the front window visor changed the A-pillar vortex shedding trajectory and thus reduced the driver’s ear pressure fluctuation. On this basis, an optimization algorithm was employed to optimize the shape of the front window visor. The main design goal was to decrease the sound pressure level (SPL) values of the driver’s left ear. Simulation results showed that the monitoring point’s SPL of buffeting noise after the visor optimization was reduced by 12.6%, compared with that of the original visor.

Optimization of wind resistance in commercial vehicles with consideration of sunroof buffeting noise

The aim of this study was to reduce the aerodynamic resistance coefficient of heavy commercial vehicles and buffeting noise that occurs when a sunroof is opened. Computational fluid dynamics was used to establish a numerical simulation model of wind resistance and buffeting noise. Analysis shows that the main influences on aerodynamic resistance are the airflow impact on the roof dome and the wake vortex behind the cab. Sunroof buffeting noise is caused by a low-pressure turbulent vortex generated at the forehead of the cab and falls off at the sunroof. A strategy for reducing the wind resistance coefficient and sunroof buffeting noise is proposed, which involves optimizing the sun visor installation angle and roof dome shape. The optimal strategy is to increase the sun visor installation angle by 4° and use the Scheme 2 roof dome. After optimization, the aerodynamic resistance coefficient of the commercial vehicle was reduced by 2.07% and the sound pressure level of sunroof buffeting noise was reduced by 18.3 dB. Hence, the effect of optimization was obvious. This work provides guidance for reducing drag and buffeting noise in commercial vehicles.

Control of Sunroof Buffeting Noise by Optimizing the Flow Field Characteristics of a Commercial Vehicle

When a commercial vehicle is driving with the sunroof open, it is easy for the problem of sunroof buffeting noise to occur. This paper establishes the basis for the design of a commercial vehicle model that solves the problem of sunroof buffeting noise, which is based on computational fluid dynamics (CFD) numerical simulation technology. The large eddy simulation (LES) method was used to analyze the characteristics of the buffeting noise with different speed conditions while the sunroof was open. The simulation results showed that the small vortex generated in the cab forehead merges into a large vortex during the backward movement, and the turbulent vortex causes a resonance response in the cab cavity as the turbulent vortex moves above the sunroof and falls into the cab. Improving the flow field characteristics above the cab can reduce the sunroof buffeting noise. Focusing on the buffeting noise of commercial vehicles, it is proposed that the existing accessories, including sun visors and roof domes, are optimized to deal with the problem of sunroof buffeting noise. The sound pressure level of the sunroof buffeting noise was reduced by 6.7 dB after optimization. At the same time, the local pressure drag of the commercial vehicle was reduced, and the wind resistance coefficient was reduced by 1.55% compared to the original commercial vehicle. These results can be considered as relevant, with high potential applicability, within this field of research.

Numerical Study on Control of Sunroof Buffeting

Sunroof has become one of the essential features of a luxury car, and it provides natural air circulation and good illumination into the car. But the primary problem associated with it is the buffeting noise which causes discomfort to the passengers. Though adequate studies were carried out on sunroof buffeting, efficient control techniques are needed to be developed from fundamental mechanism. To reduce the buffeting noise, flow modifications at the entrance of the sunroof is considered in this study. The internal portion of the car with sunroof is simplified into a shear driven open cavity, and two-dimensional numerical simulations are carried out using commercial solver, ANSYS Fluent. Reynolds averaged Navier-Stokes equation is used with the realizable k-? turbulence model. The unsteady numerical result obtained in this study is validated with the available experimental results for the dominant frequency. The prediction is good agreement with experiment. Flow modification technique is proposed to control the sunroof buffeting by implementing geometric modifications. A hump has been placed near the leading edge of the cavity which resulted in significant reduction of pressure oscillations. Parametric studies have been performed by varying the height of hump and the distance of hump from the leading edge. There is no prominent difference when the height of the hump is varied. As the distance of the hump from the leading edge is reduced, the sound pressure level decreases.

Application of Omega vortex identification method in cavity buffeting noise

The cavity buffeting noise is related to the free shear layer oscillation and the periodic vortex shedding, where weak vortices coexist with strong vortices and the strong shear phenomenon also exists at the opening of the cavity. Therefore, it is of great significance to accurately capture vortices at the opening for the control of the cavity buffeting noise. This paper first compares the Omega vortex identification method with the Q and λ2 criteria based on the large eddy simulation (LES) of the backward-facing step flow, and it is found that the Omega method enjoys the following advantages: it is not sensitive to a moderate threshold change and Ω = 0.52 can be used as a fixed threshold, it can capture both the strong and weak vortices at the same time; and it will not be contaminated by the shear. Then the Omega (Ω) method is applied to the LES of the cavity buffeting noise: the mechanism of the cavity buffeting noise is studied based on a simple cavity model firstly, and then the effects of the incoming boundary layer thicknesses and the incoming boundary layer shapes on the cavity buffeting noise are analyzed. The results show that: the Ω method clearly captures the processes of the vortex generation, development, collision and fragmentation, verifying that the generation of the cavity buffeting noise is related to the free shear layer oscillation and the periodic vortex shedding; as the thickness of the incoming boundary layer increases, the free shear layer becomes more stable and the Helmholtz resonance is avoided effectively, thereby the cavity buffeting noise is reduced effectively, adding a convexity upstream of the cavity opening to interfere the shape of the incoming boundary layer to reduce the acoustic feedback effect can reduce the cavity buffeting noise effectively.

Research on wind buffeting noise characteristics of a vehicle based on ILRN and DES-ILRN methods

In view of the unsatisfactory calculation accuracy of common turbulence models, two improved models, called improved low-Reynolds number (ILRN) k− ε and Detached EddySimulation (DES)-ILRN are proposed. Basing on the low-Reynolds number (LRN k− ε) turbulence model in this paper, revised concepts include the introduction of turbulence time scale, eddy viscosity coefficient limitation concept and separation perception model. Otherwise, the DES model is improved by introducing the ILRN model. The accuracy of the two models is validated through wind tunnel test. Then, the wind buffeting noise from rear windows is received by ILRN and DES-ILRN turbulence models, and the obtained results are compared with the road test. The accuracy of ILRN and DES-ILRN turbulence models in calculating wind buffeting noise of a real vehicle is validated by experiment. ILRN and DES-ILRN models are applied to research the wind buffeting noise, and good calculation results are obtained. They are promising methods to solve wind buffeting noise problems.

Research on the simplified vehicle window buffeting noise with a modified LRN CLES model using a transition-code based method

PurposeThis paper aims to propose a precise turbulence model for vehicle aerodynamics, especially for vehicle window buffeting noise.Design/methodology/approachAiming at the fact that commonly used turbulence models cannot precisely predict laminar-turbulent transition, a transition-code-based improvement is introduced. This improvement includes the introduction of total stress limitation (TSL) and separation-sensitive model. They are integrated into low Reynolds number (LRN) k-ε model to concern transport properties of total stress and precisely capture boundary layer separations. As a result, the ability of LRN k-ε model to predict the transition is improved. Combined with the constructing scheme of constrained large-eddy simulation (CLES) model, a modified LRN CLES model is achieved. Several typical flows and relevant experimental results are introduced to validate this model. Finally, the modified LRN CLES model is used to acquire detailed flow structures and noise signature of a simplified vehicle window. Then, experimental validations are conducted.FindingsCurrent results indicate that the modified LRN CLES model is capable of achieving acceptable accuracy in prediction of various types of transition at various Reynolds numbers. And, the ability of this model to simulate the vehicle window buffeting noise is greater than commonly used models.Originality/valueBased on the TSL idea and separation-sensitive model, a modified LRN CLES model concerning the laminar-turbulent transition for the vehicle window buffeting noise is first proposed.

Sound quality evaluation of automobile side-window buffeting noise based on large-eddy simulation

Large-eddy simulation (LES) and Detached-eddy simulation (DES) were applied to a simple cavity model to calculate the wind buffeting noise respectively. The results were verified by wind tunnel experiments. The results show that LES is more suitable for wind buffeting noise calculation. LES method was employed to calculate automobile side-window buffeting noise. The correctness of results was validated by a road test. In this paper, the acoustically calculated sound pressure level (SPL) spectral curve is used as the initial signal of the acoustic post-processing. Four psychoacoustic objective parameters namely: loudness, sharpness, roughness and fluctuation were obtained by using Matlab R2016a to compile the calculation process. Sound quality evaluation (SQE) of the vehicle is performed via most frequently used SPL and four calculated vehicle comfort index. It can be concluded that with the increase of driving velocity, SPL and loudness show an increasing trend, while roughness, sharpness and fluctuation present a decreasing trend. It can be also summarised that with the increase of window opening degree, SPL and loudness show an increasing trend, sharpness presents a decreasing trend, and roughness and fluctuation display the trend of ups and downs. The main original contribution of this paper is the accurate calculation of wind buffeting noise and the summary of the changing rule of SPL, loudness, roughness, sharpness and fluctuation with the variation of velocity and window opening degree.

Study on hybrid LESâ–“LAA method for wind buffeting noise control of vehicle rear windows

Based on the large eddy simulation (LES) and Lighthill acoustic analogy (LAA) methods, a hybrid simulation technique, so-called LESâ–“LAA, for improving wind buffeting noises generated by opening rear windows of a running vehicle is presented in this article. The wind buffeting noises are simulated by the LESâ–“LAA and experimentally verified. Some factors affecting the wind buffeting noise, such as vehicle speed and window opening scale, are investigated. To decrease the wind buffeting noises, some attempts are made by attaching absorption materials in the compartment and mounting a plexiglass baffle at an appropriate position for reducing wind noise. The results show that the calculation errors on the sound pressure level (SPL) of the LESâ–“LAA are less than 2%. The SPL of wind noise reaches a maximum value at a rear-window opening scale of 42% and is positively correlated to the vehicle speed. The wind buffeting noise of opening windows on both sides is lower than that of opening one. After mounting the baffle, the reduction of interior noise reaches to 27.26 dB. A conclusion is drawn that the proposed LESâ–“LAA method and the buffeting noise control measures are accurate, effective and feasible, which may be directly applied to vehicles and have potential for solving other aeroacoustic engineering problems.

Numerical investigation of cavity self-oscillation and noise radiation induced by turbulent flow at non-zero inclination angle.

A hybrid numerical approach was used on a three-dimensional cavity at a non-zero inclination angle of the upstream section to reveal the mechanism of self-oscillation and the characteristics of far-field sound field. In this hybrid approach, the unsteady flow physics was captured by a compressible large eddy simulation, and the far-field sound field was calculated by the FW-H integral equation, with the noise source provided by near-field calculation. The mechanism of self-oscillation was revealed based on the instantaneous flow field structure and the pressure inside the cavity. The effects of the position of opening, inclination angle and neck thickness on the frequency and amplitude of the fluctuation pressure inside the cavity were examined. Results showed that the frequency and the amplitude were sensitive to the inclination angle but not to the position of the opening. Under varying neck thicknesses, the fundamental frequencies changed, but the amplitude remained almost constant. The influences of the boundary layer thickness on the amplitude of the fluctuation pressure was also investigated. Results revealed that the oscillation was suppressed once the boundary layer thickness reached a critical value. The findings could provide a reference for a quiet car with a low sunroof buffeting noise.

A Numerical Study of Trailing Edge Serrations on Sunroof Buffeting Noise Reduction

A Numerical Study of Trailing Edge Serrations on Sunroof Buffeting Noise Reduction

A hybrid prediction for wind buffeting noises of vehicle rear window based on LES-LAA method

Based on the theories of computational fluid dynamics (CFD) and aeroacoustics, a hybrid simulation technique, the so-called LES-LAA method is proposed in this paper, for predicting the wind buffeting noises generated by opening rear windows of a running vehicle. The LES-LAA is developed by combining the large eddy simulation (LES) and the Lighthill acoustic analogy (LAA) methods. Based on the established vehicle and wind tunnel models, the wind buffeting noises from rear windows are predicted by using the proposed LES-LAA method and the obtained results are compared with experimental data. The results show that the calculation error of sound pressure level (SPL) from the LES-LAA method is less than 2%, which suggests that the proposed method has good accuracy in predicting the wind noise of the rear window of a vehicle. The wind noise when both sides of the rear window are opened at the same time is much lower than the case when just one window is opened. In conclusion, the hybrid LES-LAA technique presented in this paper is effective and feasible for predicting the wind buffeting noise, which can be applied to other types of vehicle and is a promising approach for solving other aero-acoustical engineering problems.

Analysis of Car Sunroof Buffeting Noise Based on Scale-adaptive Simulation

Analysis of Car Sunroof Buffeting Noise Based on Scale-adaptive Simulation

A psychoacoustical study of wind buffeting noise

Aerodynamic noise resulting from a vehicle moving through air at high speeds is one of the most important sources of noise perceived by the passengers. It consists of a stationary broadband signal and of modulated and fluctuating components, particularly emphasized by gusts of wind and turbulences generated by the interaction with nearby vehicles. The article reports on a study of the perception of this latter phenomenon, wind buffeting, potentially deleterious to the sound quality of a vehicle. Binaural recordings of nineteen cars were conducted in a wind tunnel with a specific module designed to simulate mild or severe buffeting. Naive and expert participants first rated the unpleasantness of the recordings played at their real levels. There were large differences of loudness between the sounds resulting mostly from the car designs, and loudness was the main factor contributing to the unpleasantness of the sounds. Participants then rated the unpleasantness of the recordings equalized to the same loudness. In that case, unpleasantness was mostly influenced by the buffeting module and related to fluctuation strength, a psychoacoustical descriptor of perceived loudness modulations. We propose an indicator of the unpleasantness of wind buffeting based on fluctuation strength in several frequency bands as well as other descriptors of the spectral balance of the sounds.

Numerical simulation of automobile side-window buffeting noise based on fluid–structure interaction

Large-eddy simulation method was employed to compute the buffeting noise of a simple deep cavity model. Compared with the results of wind tunnel experiments, the numerical results coincided well with the experimental results, which further validated the correctness of Large-eddy simulation method. Large-eddy simulation method was employed to calculate automobile side-window buffeting noise when the side-window near the driver was partially opened by 25%, and the road test data validated its correctness. The flow field results were loaded to the finite element model to compute dynamic response of the car’s windows, the weak vibration of windows was excited by the air energy exchange between interior and exterior when the car at high speed. Acoustic radiation of window structure, sound pressure levels of field points in the frequency domain, panel acoustic contribution analysis of window structure were obtained by the vibration solution for the windows. The results demonstrated that the noise radiation caused by the windows’ vibration aroused the acoustic response significantly at some certain frequencies, although side-windows buffeting noise dominated in the low frequency domain. The rear window acoustic contribution accounted for the major part of the total pressure. Compared with other three side-windows, the contribution of the partially opened side-window to the total pressure was the greatest.

PAM-FLOW를 이용한 단순차량 모델의 썬루프 버페팅 소음 해석

이 연구에서는 자동차의 썬루프 버페팅 소음을 해석하기 위해 전산유체역학을 적용한 벤치마크 결과를 제시한다. 현대자동차의 HAWT라 불리는 단순 차량모델에서 열린 썬루프 위로의 유동해석을 통해 버페팅 현상과 그 소음 수준을 모사하였으며, 해석에 사용된 소프트웨어는 ESI Group의 PAM-FLOW이다. 해석결과는 풍동에서의 시험결과와 비교되었으며, 비교적 좋은 상관관계를 얻을 수 있었다. 전산유체해석을 통해 버페팅 소음을 예측함으로써 자동차의 썬루프 설계와 개발에 매우 유용할 것으로 기대된다. This paper presents a benchmark test result of an application of computational fluid dynamics(CFD) analysis of automotive sunroof buffeting simulation. Computational analyses of flow over an open sunroof of a simple vehicle model called as HAWT(Hyundai aeroacoustic wind tunnel) model were performed to study the buffeting phenomenon and to predict the buffeting noise level and its frequency. Computations are performed for sunroofs with PAM-FLOW software which is one of powerful CFD code of ESI group. Numerical predictions are compared with result from the tunnel test measurements. It is shown that CFD analysis has great potential for sunroof design and development by predicting buffeting noise.