• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.1104-1108
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• 2007

Automobile sunroof buffeting is the tonal noise of low frequency around 20Hz. It occurs due to the acoustic feedback process between the shear layer detached from the leading edge of sunroof opening and the Helmholtz resonator-like property of a car cabin. In this paper, PIV visualization technique is applied to the unsteady flow field around sunroof opening of an SUV in the full-scale automotive wind tunnel in order to find out buffeting mechanism. A phase-marking PIV measurement method, in which image and sound pressure are recorded simultaneously, and a phase-rearrangement post-processing program were developed for capturing noise-related velocity fields without expensive synchronization systems. Through this study, some characteristics of the real-car sunroof shear layers under various deflector conditions were identified and these results can provide insights into the noise reduction mechanism of the tube-type deflector.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.3
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• pp.180-188
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• 2014

Hyundai Motor Group(HMG) carried out experimental investigation of sunroof buffeting phenomena on a simplified car model called Hyundai simplified model(HSM). HMG invited participation from commercial CFD vendors to perform numerical investigation of sunroof buffeting for HSM model with a goal to determine whether CFD can predict sunroof buffeting behavior to sufficient accuracy. ANSYS Korea participated in this investigation and performed numerical simulations of sunroof buffeting for HSM using ANSYS fluent, the general purpose CFD code. First, a flow field validation is performed using closed sunroof HSM model for 60 km/h wind speed. The velocity profiles at three locations on the top surface of HSM model are predicted and compared with experimental measurement. Then, numerical simulations for buffeting are performed over range of wind speeds, using advanced scale resolving turbulence model in the form of detached eddy simulation (DES). Buffeting frequency and buffeting level are predicted in simulation and compared with experimental measurement. With reference to comparison between experimental measurements with CFD predictions of buffeting frequency and level, conclusion are drawn about predictive capabilities of CFD for real vehicle development.

• Transactions of the Korean Society of Automotive Engineers
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• v.17 no.1
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• pp.182-189
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• 2009

The noise from the sunroof can be divided into the low frequency buffeting noise and the high frequency turbulence noise generated when a car runs at the high driving speed. The wind deflector suppresses the buffeting noise generation by accelerating the vortex shedding from the front edge of sunroof opening, and guides the flow direction so that air can pass smoothly over the sunroof opening. To reduce the buffeting noise and the high frequency noise, it is very important to locate a deflector in a proper position depending on the driving speed and the sunroof opening width. The deflector's sectional shape also plays an important role in efficiently reducing the buffeting and high frequency noise. In this paper, we determined the optimum deflector's sectional shape and examined the flow characteristics behind a sunroof deflector through CFD analysis with changing the deflector height, the driving speed and the sunroof opening width. It is found that the deflector needs to be located in the higher location to control the buffeting noise by shedding the higher frequency vortices to accelerating vortices from the sunroof front edge. The deflector may act as a new noise source at the high driving speed, then it is desirable to put the deflector at the proper height to reduce the flow fluctuations and the noise generation. We also made a road test to verify CFD analysis results in this study.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.3
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• pp.198-204
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• 2014

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.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11b
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• pp.166-169
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• 2005

The best sunroof wind noise quality is mainly related to the sunroof deflector which affects both low-speed buffeting and high-speed aerodynamic noise. An automatic deflector-moving and noise-measuring apparatus is developed to obtain hundreds of measuring data which haven't been available by hand. With an additional program for fast and easy noise analysis, this device leads quickly to the better position and angle of the deflector. Now, the 'better' means the lower noise level and the robuster design solution. From these kinds of better solutions, more meaningful guidelines on the deflector design and sunroof wind noise reduction can be suggested.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.3
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• pp.205-212
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• 2014

In this paper, sunroof buffeting analysis for Hyundai simple model(HSM) is studied computationally. For validation, the velocity profile of boundary layer around the opening of HSM was obtained and compared with experimental results. The analysis of sunroof buffeting is done in two parts. First a steady state solution is obtained using the Reynolds Averaged Navier Stokes (RANS) solver, and then the computed flow field information is used as input for CAA++. Second transient simulation by CAA++ is performed for the peak sound pressure levels and peak frequencies of buffeting noise over the ranges of flow velocities. The benchmark results of frequency and sound pressure levels showed the general phenomena and matched well with the experimental data obtained by Hyundai Motor Car.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.3
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• pp.213-218
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• 2014

CFD flow simulation of vehicles with open sunroof and passenger window help the automotive OEM(original equipment manufacturer) to identify the low frequency noise levels in the cabin. The lock-in and lock-off phenomena observed in the experimental studies of sunroof buffeting is well predicted by CFD speed sweep calculations over the operating speed range of the vehicle. The trend of the shear layer oscillation frequency with vehicle speed is also well predicted. The peak SPL from the CFD calculation has a good compromise with the experimental value after incorporating the real world effects into the CFD model by means of artificial compressibility and damping correction. The entire process right from modeling to flow analysis as well as acoustic analysis has been performed within the single environment i.e., STAR-CCM+.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.3
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• pp.171-179
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• 2014

Sunroof buffeting is one of the most critical issues in the vehicle wind noise phenomena. The experimental approach to solve this issue typically requires a lot of time and resources. To reduce time and cost, the numerical approach could be taken, which can also privide more insights into physical phenomena involved in sunroof buffeting, only if the accuracy in its predictions are guranteed. The benchmark test of various numerical solvers is carried out for the buffeting behavior of a simplified vehicle body, the Hyundai simplified model(HSM). The results of each solver are compared to the experimental measurements in a Hyundai aeroacoustic wind tunnel(HAWT) at various wind speeds. In particular, acoustic response tests were performed and the results were provided prior to all simulations in order to consider the real world effects that could introduce discrepancies between the numerical and experimental approaches. Through this study, most solvers can demonstrate an acceptable accuracy level for actual commercial development and high precision experimental data and computational prediction priories can be shared in order to promote the numerical accuracy level of each numerical solver.

• The Journal of the Acoustical Society of Korea
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• v.37 no.5
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• pp.285-291
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• 2018

In the present study, flow characteristics and wind noises around the sunroof opening are analyzed variation with panoramic sunroof deflector angle. A mesh deflector is attached to reduce wind noise while a car is driving with the panoramic sunroof opening. A new forward inclined type deflector was invented to improve wind noise. The effect of this new concept of mesh deflector on the open-panoramic flow characteristics and wind noises were studied with CAT (Computer Aided Test) and wind tunnel test, which shows the reduction of open-panoramic wind noises such as sunroof buffeting, sunroof booming, and turbulent noise. Therefore, the forward inclined type deflector can efficiently improve wind noise with the same production cost.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.3
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• pp.189-197
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• 2014

A simplified model in the shape of a wedge box with an opening on the roof was used to generate buffeting conditions at HMC. These measurements performed in controlled conditions are intended to validate the ability of CFD tools to predict buffeting. The results obtained by PowerFLOW are presented in this paper for buffeting and for the boundary layer development on the roof of the model when the roof opening is closed. The flow mechanisms that explain the behavior of the experimental sound pressure level(SPL) curve are described, and an improved setup is used to reproduce the flow structures that lead to the measured SPL.