Large Eddy Simulation of Base Drag Reduction with Jet Boat-tail Passive Flow Control

Abstract

A Large Eddy Simulation (LES) of base drag reduction for automotive side view mirrors using passive Jet Boat-Tail (JBT) passive flow control is conducted. The JBT passive flow control technique is to introduce a strong jet by opening an inlet in the front of a bluff body, accelerate the jet via a converging duct and eject the jet at an angle toward the center of the base surface. The high speed jet flow entrains the free stream flow to energize the base flow and increase base flow pressure. The LES investigation of flow over a JBT mirror and baseline mirror model is conducted with a low diffusion E-CUSP scheme with fifth order WENO scheme for the inviscid term and fourth order central differencing for the viscous term. The LES calculation indicates that strong passive flow jet enhances the flow entrainment, which mixes with the main flow and transfers the energy from the main stream to the base flow by increasing base flow pressure, thus reducing pressure drag. The preliminary analysis of the flow structures with wake and jet interaction is presented.