Experimental Investigation of the Effect of Camber on the Aerodynamic Characteristics of Airfoils in Ground Effect

Abstract

In the present paper, results from an experimental investigation of aerodynamic ground effect on two airfoils are presented. The flow characteristics over a symmetrical airfoil (NACA 0015) and a cambered airfoil (NACA 4415) were studied in a low speed wind tunnel. Experiments were carried out by varying the angle of attack from 0° to 10° and ground clearance from zero to one chord length. Pressure distribution on the surface of the airfoil was obtained with the help of pressure tappings. Mean velocity distributions were obtained over the surface of the airfoil. Profiles of mean velocity and turbulence intensity were obtained in the wake region at 0.5 and 1.0 chord length downstream of the trailing edge. It is found that pressure increases on the lower surface as the ground is approached. The flow accelerates over the airfoil, and a considerably higher mean velocity is observed near the suction peak location. For the symmetrical airfoil, the mean velocity over the surface was found to increase by nearly 30%, while for the cambered airfoil, an increase of nearly 60% was recorded for an angle of attack of 7.5°. The flow was found to separate almost near the trailing edge for angles of attack upto 10°, resulting in a thinner wake region and lower turbulence intensities for the symmetrical airfoil; while for the cambered airfoil, an early separation for an angle of attack of 10° was observed. Measurements in the wake region showed a defect in mean velocity profile at the corresponding values of ground clearance. For lower angles of attack, turbulence levels were higher in the wake region for the symmetrical airfoil, while for an angle of attack of 10°, very large defect in velocity was observed for the cambered airfoil model and the minimum velocity reduced to 20% of the freestream velocity.