Airfoil aerodynamics in ground effect for wide range of angles of attack

The aerodynamics and flow physics of aNACA4412 airfoil in ground effect for a wide range of angles of attack from-4 to 20 deg are investigated by numerical simulations. The compressible Reynolds-averaged Navier-Stokes equations and shear-stress transport k-ω turbulence model equations are solved using the finite-volume method. Analyses of the computed results show that the angle of attack versus height (above the ground) plane can be divided into three regions based on the sign of the lift increment value: region I of positive ground effect, and regions II and III of negative ground effect. For low-to-moderate angles of attack, when the ride height is reduced, the airflow is blocked in the convergent passage between the lower surface of the airfoil and the ground, resulting in increase of pressure on the lower surface of the airfoil. As a consequence, the effective angle of attack decreases, and there is less upward deflection of the streamlines, resulting in an increase in pressure on the upper surface of the airfoil. At high angle of attack, when the ride height is reduced, the adverse pressure gradient along the chordwise direction increases, resulting in a larger region of separated flow. Additionally, for negative angle of attack generating negative lift, the airflow accelerates in the convergent-divergent passage between the lower surface and the ground due to the Venturi effect, resulting in a large suction on the lower surface of the airfoil.