Low Drag Automotive Mirrors Using Passive Jet Flow Control

This paper introduces and proves a novel automotive mirror base drag reduction method using passive jet flow control. The new concept is to open an inlet at the front part of the mirror, introduces the airflow via a converging duct, and ejects the jet surrounding the mirror surface at an angle toward the center of the mirror. The jet harnesses the energy from the free stream by jet mixing with the main flow via large coherent structures, entrains the main flow to energize the base flow, reduces the wake size and turbulence fluctuation, and ultimately significantly decreases the drag. Above phenomena are proved by wind tunnel testing with PIV and drag force measurement and CFD large eddy simulation (LES) calculation. Two jet mirrors with different inlet areas are studied. The jet mirror tunnel 1 has a smaller inlet area, and the jet mirror tunnel 2 has a 4.7 times larger inlet area. The wind tunnel testing is only done for the baseline and jet mirror tunnel 1. LES is used to study all the three mirror configurations. Both the wind tunnel testing and LES indicate that the jet mirror tunnel 1 reduces the drag by about 18% with smaller wake width. The LES indicates that the jet mirror tunnel 2 with larger inlet area further reduces the wake and achieves a drag reduction of 39%. This paper is only for proof of the concept and no design optimization is done. It is believed that there is a large room to further reduce the drag with a systematic design optimization.