Abstract
At present, there are some researches focusing on optimization of aerodynamic noises on rear view mirrors, but researches on bionic noise reduction of rear view mirrors are rarely reported. Therefore, with an original rear view mirror as the basic model, the paper applied a head convex hull of a dung beetle to the original rear view mirror cover to obtain a bionic rear view mirror, then conducted numerical computation for aerodynamic noises of the bionic rear view mirror and compared the computational results with the original model. Finally, in order to verify correctness of computational results of aerodynamic noises of the rear view mirror, wind tunnel test was conducted on the rear view mirror. Experimental and numerical simulation results were highly consistent in the whole frequency band, so the wind tunnel test could be replaced by numerical simulation. Only one obvious vortex was behind the bionic rear view mirror, but two obvious vortexes with the opposite rotation directions were behind the original rear view mirror. The bionic rear view mirror did not present vortexes near the lateral window, so impacts of vortexes on noises in the vehicle could be eliminated effectively. Pressure difference in front of and behind the bionic view mirror was smaller than the pressure difference in front of and behind the original rear view mirror. Pressure resistance caused by the convex structure outside the rear view mirror was reduced, so noise reduction could be promoted. The convex structure mainly affected the aerodynamic noise in mid-high frequency regions. Compared with the original rear view mirror, noise reduction effects of the bionic rear view mirror were obvious, where the noise reduction amplitude reached 10dB. Noise source size and intensity of the bionic rear view mirror were reduced obviously.
Highlights
When the running speed of a vehicle reaches a certain value, airflows would intensely hit the body, so the reversed vehicle performance in the construction space will be affected
Noises caused by running airflows include: noises caused when air enters a vehicle through door windows; aerodynamic noises caused by vortexes which are generated when airflows get contact with the body, as well as vibration noises caused by friction between air and the body; vibration noises caused by convex structures on the body
The vortexes near the lateral window surface had higher intensity and velocity; intensity of the vortexes near the rear view mirror edge was relatively weak; and the shape was presented to an oval shape along the airflow flowing direction
Summary
When the running speed of a vehicle reaches a certain value, airflows would intensely hit the body, so the reversed vehicle performance in the construction space will be affected. The wind tunnel test is an experimental method which could simulate air flowing around the rear view mirror, quantify effects of airflows on objects and observe physical phenomena through manual generation and control for the airflows. It is an indispensable part at the design stage. For example: Chen [12] applied wind tunnel experiments to test aerodynamic noises at 8 observation points in a wake flow region of rear view mirrors. With an original rear view mirror as the model, the paper applied a head convex hull of a dung beetle to the rear view mirror cover, conducted numerical computation of aerodynamic noises of the bionic rear view mirror and compared the computational results with the original model
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