The Combination of Rear Flaps and Plasma Actuators for the Drag Reduction of a Square-Back Bluff Body

Abstract There is a significant need to reduce the aerodynamic drag of ground vehicles. As a result, the active and passive methods of flow control around bluff bodies have been extensively studied to improve aerodynamic performance. In this study, the drag reduction by combining rear flaps and plasma actuators (PAs) is experimentally investigated. PAs are modern active flow control devices that leverage non-thermal plasma, whereas flaps are traditional passive flow control devices. Flaps and PAs are mounted on the square back of the truck model, and the effect of the flap mounting locations (top or side of the model), flap angle, and flap length are investigated at $Re_H=1.58\times10^5$. For both top and side flaps, the longer flaps result in greater drag reduction compared to shorter flaps in the absence of PA actuation. However, additional drag reduction with PA actuation is minimal for the longer flaps, and the flap angle at which drag reaches a local minimum remained unchanged. This is attributed to an increase in pressure drag on the flap as the flap angle increases when the flow is attached to the flap surface. In contrast, PA actuation with shorter flaps demonstrates drag reduction, due to the smaller surface area of the flaps. These results suggest that optimising the flap angle and length is a promising strategy to maximise the aerodynamic benefits of PA actuation and reduce the drag on bluff bodies.