Aerodynamics of a transonic airfoil in ground effect

The wing-in-ground-effect (WIG) aircraft operates with larger lift-to-drag ratio compared to a conventional aircraft at low subsonic Mach numbers. To increase traffic volume of WIG aircraft, one possible way is to increase flight speed, which can result in transonic flow. Currently studies on transonic flight in ground effect are few. The goal of this paper is to study aerodynamics and flow physics of typical transonic RAE2822 airfoil at angles of attack from 0 to 12 deg and Mach numbers from 0.5 to 0.8 in ground effect by varying the ground clearance. The compressible Reynolds-averaged Navier-Stokes equations with Spalart-Allmaras turbulence model are solved using FLUENT. For flight near the ground, some interesting shock formations are obtained due to transonic flow. For unsteady shock buffet on the upper surface, the buffet boundary in angle of attack (AOA)-Mach numberMplane shrinks with the decreasing ground clearance. Compared to the unbounded flowfield, there exists a steady shock on the lower surface of the airfoil in ground effect for low AOAs because the channel between the lower surface of the supercritical airfoil and the ground is of typical converging-diverging shape, resulting in decrease in lift and increase in drag.