Flow over thick airfoils in ground effect - an investigation on the influence of camber

Results from an experimental investigation of aerodynamic ground effect on three airfoils, NACA 0015, 4415 and 6415, carried out in a low speed wind tunnel are presented. The pressure distribution on the airfoil surface was obtained from pressure tappings. Mean velocity measurements were performed over the surface of the airfoil and velocity contours were plotted. Measurements of mean velocity and turbulence intensities were performed in the wake region at two locations. Experiments were carried out by varying the angle of attack from 00 to 100 and ground clearance from the minimum possible value to one chord length. It was found that high values of pressure coefficient are obtained on the lower surface when the airfoil is close to the ground. This region of high pressure extended almost over the entire chord length for higher angles of attack. The flow was found to accelerate over the airfoils with the highest acceleration observed for NACA 4415 and lowest for NACA 6415. For NACA 4415 model, a very high mean velocity is observed near the suction peak location. For this airfoil, the flow was found to separate from the surface for angles of attack 100 and above, resulting in considerably lower velocities over the surface and a thick and highly turbulent wake region.