Designing and Optimizing Side-View Mirrors

Abstract: Today, reducing the carbon dioxide emissions is vital. The carindustry has a responsibility to reduce the fuel consumption and willthereby reduce carbon dioxide emissions. One of the main questionsin the automotive industry how to go about this. One possibility isto change the propulsion system. Another option is to reduce theaerodynamic drag of the car; the topic of this thesis. The drag is ofgreat importance when it comes to velocities over 60 kph.There are many parts of the car that contribute to drag. One suchpart is the (side-view) mirrors. The mirrors increase the total amountof drag by 2-7 percent. There numerous regulations and legal demandswhen it comes to mirrors due to the aspects of safety. Moreover, themirrors affect the soiling of the windows which creates yet anothersafety issue. Dirty windows reduce the visibility for the driver.Many different mirror designs and parameters have been investigated.To get the amount of drag, computer simulations (CFD)have been done. The car which the mirrors have been attached to isa Mercedes-Benz A-class (W168) quarter scale model. Wind tunneltesting (at FKFS, Stuttgart) in quarter scale has been done for correlation.(The correlation did not match the CFD well, however, thetrends were the same.)After various tests, one can observe that small changes to the mirror,such as change edges radius, inclinations, adding gutters, andedges, affect the flow both around the mirror and in the rear of thecar. The best drag reduction was achieved when the housing curvatureof the mirror was changed from rather bulky to flatter model whichproduced the same drag reduction as having no mirrors at all.The mirror plays a major role in drag contribution for the entirecar and therefore mirror optimization is considered very important.Mirror optimization is not an easy task due to uncertainties in theCFD simulations of a few drag counts which makes it impossible totrust all findings. In order to find a good mirror design, a combinationof wind tunnel testing in full scale, and CFD simulations is necessary.Mirror design optimization shows great potential.