Experiments on the Aerodynamics of a Cambered Airfoil in Ground Effect

The flow characteristics over a NACA4412 airfoil are studied in a low turbulence wind tunnel with moving ground simulation at a Reynolds number of 3.0 × 10^5 by varying the angle of attack from 0^o to 10^o and ground clearance of the trailing edge from five percent of chord to hundred percent. The pressure distribution on the airfoil surface was obtained, velocity survey over the surface was performed, wake region was explored, and lift and drag forces were measured. To ensure that the flow is 2-D, PIV measurements were performed. A strong suction effect on the lower surface at an angle of attack of 0^o at the smallest ground clearance caused laminar separation well ahead of the trailing edge. Interestingly, for this airfoil, a loss of upper surface suction was recorded as the airfoil approached the ground for all angles of attack. For angles up to 4^o, the lift decreased with reducing ground clearance, while for higher angles, it increased due to higher pressure on the lower surface. The drag was higher close to the ground for all angles investigated mainly due to the modification of the lower surface pressure distribution.