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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.

This paper conducts numerical simulation and wind tunnel testing to demonstrate the passive flow control jet boat tail (JBT) drag reduction technique for a heavy duty truck rear view mirror. The JBT passive flow control technique is to introduce a flow 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, increase the base pressure, reduces the wake size, and thus reduce the drag. A baseline heavy duty truck rear view mirror is used as reference. The mirror is then redesigned to include the JBT feature without violating any of the variable mirror position geometric constraints and internal control system volume requirement. The wind tunnel testing was conducted at various flow speed and yaw angles.