A three-element airfoil operating in ground effect was investigated numerically.The compressible Navier-Stokes equations were solved by the finite-volume method.Spalart-Allmaras (S-A) turbulence model was used.Slipping wall was used to simulate the relative movement.The effects of flight height on the aerodynamics of the multi-element airfoils were found obviously as compared with clean airfoils.The results indicate that

with the reduction in height

the lift increases for the multi-element airfoil

but decreases for the clean airfoil

while the drag and nose down moment decrease for both airfoils.The cause of the reduction of lift lies in that

the losses of suction at upper surface are more than the increases of pressure at lower surface.The separated region becomes larger with the decline of the height.