This paper studies the aeroacoustics of the side view mirrors by wind tunnel tests and numerical simulations. The mirror is placed on a table in the wind tunnel test. Based on the experiment results, a numerical analy...This paper studies the aeroacoustics of the side view mirrors by wind tunnel tests and numerical simulations. The mirror is placed on a table in the wind tunnel test. Based on the experiment results, a numerical analysis model is established to analyze the acoustic field in the wake of the side view mirror by the Large Eddy Simulation（LES）. The flow field and the noise level of two different side view mirrors are compared in the simulation. It is shown that, with the serration structures applied onto the mirror surface, the turbulence zone and the pressure fluctuation in the wake of the bionic model are improved effectively, which helps its flow control and noise reduction. Meanwhile, as is shown in the noise spectra, when the noise frequency is over 500 Hz, for the bionic mode, the noise is reduced to a lower level than with the original one, which further shows its effectiveness in the noise reduction.展开更多
While driving a car at high speed cruising, the mirror surface of side-view mirrors happens to vibrate. The vibration often leads to image blurs of objects reflected in the mirror. Once the phenomena happen, drivers c...While driving a car at high speed cruising, the mirror surface of side-view mirrors happens to vibrate. The vibration often leads to image blurs of objects reflected in the mirror. Once the phenomena happen, drivers cannot clearly identify the approaching vehicles from the rear. The paper aims to clarify the vibration modes of side-view mirror experimentally and to capture forces on the mirror surface induced by separating vortices around the mirror numerically. Experimental study clarified two findings. One is that the mirror has the primary natural frequencies of 25, 30 and 33 Hz. The other is that vibrations of the mirror increase in proportion to flow velocity and their frequencies have peak values at 120 and 140 km/h. The frequencies of the mirror vibration coincide completely with the primary natural frequencies. In order to capture the external forces vibrating the mirror surface, numerical study was performed by unsteady air-flow analyses. Relationships between flow velocity fluctuations close to the mirror surface and pressure fluctuations on the mirror surface were investigated. It was found that the two power spectra have peak values at the same frequency of 24.4 Hz at 120 km/h. This shows that flow velocity fluctuations with the frequency of 24.4 Hz affect directly pressure fluctuations on the mirror surface. Numerical analyses clarify that the frequencies of shedding vortices are 24.4 Hz at 120 km/h and 28.3 Hz at 140 km/h. The frequencies of mirror vibration are very close to those of flow fluctuations. This shows that the frequencies of the mirror vibration have much to do with the frequencies of the forces induced aerodynamically by vortex shedding. Therefore it follows that image blurs at high speed cruising are caused by resonance phenomena that the mirror surface resonates with the frequencies of shedding vortices around the mirror.展开更多
基金Project supported by the State’s Key Project of Research and Development Plan of China(Grant No.2016YFB0101601-7)the Special planning project of Jilin Province(Grant No.SXGJSF2017-2-1-5)the Science and Technology Develop-ment Project of Jilin Province(Grant No.20160101283JC)
文摘This paper studies the aeroacoustics of the side view mirrors by wind tunnel tests and numerical simulations. The mirror is placed on a table in the wind tunnel test. Based on the experiment results, a numerical analysis model is established to analyze the acoustic field in the wake of the side view mirror by the Large Eddy Simulation（LES）. The flow field and the noise level of two different side view mirrors are compared in the simulation. It is shown that, with the serration structures applied onto the mirror surface, the turbulence zone and the pressure fluctuation in the wake of the bionic model are improved effectively, which helps its flow control and noise reduction. Meanwhile, as is shown in the noise spectra, when the noise frequency is over 500 Hz, for the bionic mode, the noise is reduced to a lower level than with the original one, which further shows its effectiveness in the noise reduction.
文摘While driving a car at high speed cruising, the mirror surface of side-view mirrors happens to vibrate. The vibration often leads to image blurs of objects reflected in the mirror. Once the phenomena happen, drivers cannot clearly identify the approaching vehicles from the rear. The paper aims to clarify the vibration modes of side-view mirror experimentally and to capture forces on the mirror surface induced by separating vortices around the mirror numerically. Experimental study clarified two findings. One is that the mirror has the primary natural frequencies of 25, 30 and 33 Hz. The other is that vibrations of the mirror increase in proportion to flow velocity and their frequencies have peak values at 120 and 140 km/h. The frequencies of the mirror vibration coincide completely with the primary natural frequencies. In order to capture the external forces vibrating the mirror surface, numerical study was performed by unsteady air-flow analyses. Relationships between flow velocity fluctuations close to the mirror surface and pressure fluctuations on the mirror surface were investigated. It was found that the two power spectra have peak values at the same frequency of 24.4 Hz at 120 km/h. This shows that flow velocity fluctuations with the frequency of 24.4 Hz affect directly pressure fluctuations on the mirror surface. Numerical analyses clarify that the frequencies of shedding vortices are 24.4 Hz at 120 km/h and 28.3 Hz at 140 km/h. The frequencies of mirror vibration are very close to those of flow fluctuations. This shows that the frequencies of the mirror vibration have much to do with the frequencies of the forces induced aerodynamically by vortex shedding. Therefore it follows that image blurs at high speed cruising are caused by resonance phenomena that the mirror surface resonates with the frequencies of shedding vortices around the mirror.
