Research On The Flow Field Characteristics Influenced By Outside Rearview Mirror Of A Car

With the increasing number of cars, automobile noise takes up larger proportion in thenoise pollution,bringing a negative impact to people’s work and life and even harmingpeople’s health. Aerodynamic noise is an important part of automobile noise. As the researchon the other noise reduction get into bottleneck, aerodynamic noise is getting more and moreattention. As one of the major aerodynamic noise sources, rear-view mirror is outside of thecar body and produces strong turbulence flow structure behind the rearview mirror. Theturbulence structure move regularly and beat against the windows, causing wind noise. Sostudy on the effect of outside rearview mirror on the aerodynamic characteristics of the sidewindow is of great significance. In this thesis, Model1without rearview mirror and Model2and Model3with rearview mirror were analyzed to study the influence of the rearviewmirror to its aerodynamic characteristics in the wake region.Now the research on the rear-view mirror mainly includes two aspects: the influence ofthe rearview mirror on the wake aerodynamic characteristics and the noise contribution towind noise generated in this region. The experimental method and simulation method werecombined to study these two aspects.First, wind tunnel test were carried out for the three models, including the oil filmexperiment and pressure coefficient measurement on the side window. The wind speed was80km/h、100km/h and120km/h. Measurement of pressure coefficient of Model1and Model3suggests: the outside rearview mirror causes the pressure coefficient to decrease in thewake region, making it easier for the region to form vortex. The oil film experiment ofModel1and Model3confirmed that: strong turbulence was produced in the backflowbehind the mirror due to the rearview mirror, and the position of A-pillar reattached line waschanged.Then the vehicle model is established for steady state simulation computation. Thepressure coefficient of11points on the side window is calculated and the reattached line of the vortex was obtained. The results showed that the simulation results and experimentalresults are identical with each other. The vehicle coordinate system is established. Thesimulation results found two vortex in different direction were formed in xy plane and xzplane through the rearview mirror. This is because there is a low pressure area in therearview mirror wake region, the air flow passing by the rearview mirror provides energy forthe vortex, and air flow moved to the center of the backflow due to the pressure difference tothe posterior. Vortex in the two plane is divided into two parts: external eddy current which isnot occurring and the internal vortex flow.Then transient calculation were conducted for the three models. The sound pressurelevel of the11monitoring points on the side window of Model2and Model3is higher by11.75-17dB than that of Model1. It suggests the turbulence in the circulation region behindthe rearview mirror leads to the rise of wind noise and study on the noise reduction ofrearview mirror has certain potential. Through the data comparison, it was found that withthe increase of speed the proportion of wake turbulence noise caused by rearview mirrorincreased. Study on the aerodynamic characteristics of rear view mirror in high speed is veryimportant.Finally, on the basis of studying the aerodynamic characteristics of rearview mirror, somesuggestions on retrofit work were put forward.