Bluff Body Drag Reduction Using Passive Flow Control of Jet Boat Tail

This paper conducts experimental study and numerical large eddy simulation for the drag reduction effect of jet boat-tail passive flow control on bluff body models. The jet boat-tail for bluff bodies operates by surrounding a converging duct around the end of a bluff body where the base surface is located. The duct captures free stream and forms a high speed jet angled toward the center of the bluff body base surface circumferentially to have the effect of a boat tail. A rectangular prism bluff body representative of various motor vehicle shapes such as trucks, vans, SUVs is used in this study. The numerical Large Eddy Simulation shows that the jet boat-tail sucks in the forebody boundary layer due to the low base pressure and significantly thins the boundary layer. The jet interacts with the shear layer and creates large vortex structures that entrain the freestream to base flow and energize it. The base pressure with the jet boat-tail is increased and the wake velocity deficit is reduced, resulting in a significant drag reduction. The Large Eddy Simulation indicates a significant drag reduction of 15%. The baseline and jet boat-tail configuration were also tested in a wind tunnel using 3D Stereo Particle Image Velocimetry at the speed of 10m/s and 30m/s. The wind tunnel testing shows a significant wake velocity deficit reduction by using jet boat-tail passive flow control, which is consistent with the drag reduction results of the Large Eddy Simulation.