Experimental Study on Ground Effect of a Wing with Tip Sails

The experimental results of Ground Effect of a wing mounted with tip sails are introduced in the paper. The objective of the study is to simulate and evaluate the flow control efficiency of primary feathers to the wing of a pelican skimming over water surface. Compared with a NACA4412 prototype wing, the experimental results show that, for the same ground clearance, the lift coefficient of the tip-sails wing increases significantly and the stalling angle of attack decreases, the drag coefficient keeps nearly unchanged at small angle of attack (AOA) and decreases obviously at higher AOA. The tip sails increase the slope of the lift coefficient curves, the maximum lifts rise by 11.03% and 8.26% compared to those of the prototype wing for ground clearance h*=0.15 and h*=0.5, respectively. The lift-to-drag ratio is improved as well at higher AOA and lift coefficient range. The vorticity contours of tip vortices of two types of wings show that, the vortices cores move outboard due to the ground effect. The concentrated vorticity distribution of the prototype wing is scattered by the tip sails, and spread over a larger area. For the tip-sails wing, the vortices at h*=0.15 are scattered much more than the vortices at h*=0.5 and the intensity of the vortex is much lower. The dissipation of the tip vortices is accelerated due to the inhibition by the ground clearances and the spreading by the tip sails to the vortices.