Ground effects on the aerodynamics of a wing with slot type distributed propulsion system for VTOL applications

Abstract During take-off of a vertical take-off and landing (VTOL) aircraft, ground effects can cause a downward force on the aircraft body and wings. The downward force could substantially reduce the payload of the aircraft, which is undesirable. This paper investigates the ground effects related to VTOL applications with distributed propulsion. A slot jet is used to simulate the distributed propulsion system. A model of a wing with a slot jet placed near the trailing edge of the wing is investigated. The slot jet is almost perpendicular to the ground to provide a vertical thrust. Experimental and numerical methods are used to investigate the aerodynamic performance of this model. Theoretical analysis is carried out to understand the formation mechanism of the low pressure region on the lower surface of the wing, which causes the downward force. The flow physics of the jet inducing ground vortex is investigated. It is found that the convection term in the ground vortex area is the main source of the pressure reduction. Based on the flow mechanism, a redesigned configuration is proposed to reduce the negative effect of the ground vortex. The flow structures such as the tip vortex are also investigated.