Kang-Duck Ih

Characterization of Buffeting Noise Through a Rear Window in an Automobile Using LBM

ABSTRACT Buffeting noise through a rear window in an automobile is investigated by using lattice Boltzmann method. The generation mechanism of the buffeting noise can be understood as the resonance mecha-nism in a Helmholtz resonator, which is driven by the convecting vortex in a shear-layer flow over the neck of the resonator. Two methods to suppress the buffeting noise are proposed, and their ef-fects are quantitatively assessed. Opening front window reduces the observed buffeting tonal noise by 25 dB and the overall SPL by 4 dB, and the installation of a Helmholtz resonator acting as a dy-namic damper reduces the tonal component that by 35 dB and the overall SPL by 10 dB. * 1. 서 론 삶의 질에 대한 관심의 증가와 관련 기술이 발전함에 따라 각종 산업기기의 소음저감에 대한 연구들이 활발히 진행되고 있다 (1) . 그 중 일상생활에 매우 밀접한 자동차의 경우 소음이 가장 중요한 성능지표의 하나로 인식되고 있는 실정이다. 소음은 소음발생원리에 따라 구조진동소음과 공력소음으로 대별할 수 있다. 자동차와 같은 운송기계는 운행속력에 따라 공력소음의 상대적 중요도가 크게 증가하는데, 판매된 지 3개월이 지난 차량의 고객불만 점수를 조사하여 발표하는 IQS-3의 감점순위에서 볼 수 있듯이 (2) 공력소음이 자동차 소음의 주요한 소음원으로 작용하고 있다. 이러한 자동차 공력소음은 다시 엔진소음과 차체소음으로 구별할 수 있는데, 관련 기술의 발전과 더불어 엔진소음이 상대적으로 많이 저감됨에 따라 최근에 차체소음의 개선에 대한 요구가 높아지고 있다. 자동차 차체공력소음은 자동차 외부의 공기 흐름에 의해 발생하는 공력소음을 말하며, 소음의 음압레벨(sound pressure level)은 외부 유속에 매우 의존한다

Modeling and Simulation of Road Noise by Using an Autoregressive Model

ABSTRACT A new method for the simulation of the vehicles interior road noise is proposed in the present study. The road noise model can synthesize road noise of a vehicle for varying driving speed within a range. In the proposed method, interior road noise is considered as a stochastic time-series, and is modeled by a nonstationary parametric model via two steps. First, each interior road noise signal, obtained from constant speed driving tests performed within a range of speed, is modeled as an au-toregressive model whose parameters are estimated by using a standard method. Finally, the parame-ters obtained for different driving speeds are interpolated based on the varying driving speed to yield a time-varying autoregressive model. To model a full band road noise, audible frequency range is divided into an octave band using a wavelet filter bank, and the road noise in each octave band is modeled. * 기 호 설 명 a k : k 번째 모수 e ( t ): 스토캐스틱 시계열 모형의 잔여 n a : 자기회귀 모형의 차수 u ( t ): 주행 속도

Benchmark Test of CFD Software Packages for Sunroof Buffeting in Hyundai Simplified Model

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.

Development of an active deflector system for sunroof buffeting noise control

Sunroof buffeting noise is annoying to drivers and passengers. The conventional method for suppressing sunroof buffeting noise is to use passive deflectors. A recent trend has been large sunroof openings, such as panoramic sunroofs, in accordance with customer preferences for a feeling of openness. Since sunroof buffeting noise tends to become louder as the sunroof opening area becomes larger, a conventional passive deflector may not be a solution in this case, and a new effective method for reducing the sunroof buffeting noise is required. Previous work showed that a strong, self-sustained tonal noise, generated from a Helmholtz resonator exposed to a grazing flow, could be significantly reduced by closed-loop control of an active deflector installed near the upstream edge of the resonator opening. The active deflector system is a cascade of a microphone sensor mounted inside the cavity, controller, power amplifier, and deflector mechanism vibrated by a voice coil actuator. Since the acoustic pressure inside the cavity is influenced by the shear layer modified by the active deflector, the active deflector and acoustic response of the cavity form a closed-loop control system. The main objective of the present study is to implement this technology on a real vehicle and evaluate whether the technology can be utilized to suppress sunroof buffeting noise. A simple active deflector system was assembled and installed in a compact-sized hatchback car with a sunroof opening length of 460 mm. The active deflector system was tested both in a wind tunnel and on a proving ground. The test results showed that the active deflector reduced the sunroof buffeting noise by as much as 25 dB. The active deflector was shown to be stable and robust regardless of changes in the wind speed and wind yaw angle.