Effect of ground on flow characteristics and aerodynamic performance of a non-slender delta wing

Abstract

The aerodynamic performance and the structure of vortical flow on a delta wing are affected by the influence of the ground in take-off and landing stages. In this context, the effect of the ground on a delta wing having a sweep angle of 40° was investigated by employing Particle Image Velocimetry (PIV), aerodynamic force measuring system and the dye flow visualization technique. Flow characteristics of delta wing were examined under two different angles of attack, α=8° and 11° and variation of the distance between trailing edge of the wing and ground, h normalized with the root chord length, c of the wing. It was observed that the existence of the ground attenuates the magnitude of peak values of primary and secondary vortices due to incomplete development of vortices. The ground effect caused the outboard movement of the leading-edge vortex in a spanwise direction as well as an increase in the size of vortices. Furthermore, the presence of the ground induced a decrease in Strouhal number, St due to the slowing down of vortex formation. Lift and drag coefficient, CL, and CD of the delta wing were observed to increase with descending from unbounded flight region into ground effect region. Finally, it was found that CL/CD increases by reducing the distance between ground and wing, h/c, and a rise of CL/CD is much more effective under the lower angles of attack, α.