A Numerical Comparative Study of the Selected Cambered and Reflexed Airfoils in Ground Effect

Abstract

When a wing gets closer to the ground, the distortion of the flow and the dynamic air cushion have a positive influence on the aerodynamic characteristics. The vessels that utilize the advantage of this phenomenon in its operation are known as “Wing-in-ground effect craft” or WIG. However, the aerodynamic forces in ground effects are different from free stream flight, especially close to the ground. The center of pressure movement was found to be more complicated and varies with the ground clearance, angle of attack, and the airfoil profile which results in pitching instability in some cases. In this study, a numerical study comparing the aerodynamic characteristics of three commonly used airfoils and one reflexed airfoil in ground effect was carried out with the ground clearance ratio varying from 5% to 100% of the chord at a Reynolds number of 3 10⁶ over a wide range of angles of attack from 0° to 20°. As expected, the high-cambered airfoil has the highest lift-to-drag ratio, but the stall occurs at a smaller angle of attack, especially at low ground clearance. It also has a greater center of pressure travel with a strong nose-down moment. The expected reduction of the movement of the center of pressure was obtained in the reflexed airfoil, resulting in better pitching stability at the expense of performance. The performance of the flat-bottom airfoils is compromised between the high-cambered and reflexed airfoil.