The Effect of Large Droplet and Spanwise Ridge Ice Accretion on the Aerodynamic Performance of Swept Wings

Wind tunnel tests were performed on an 8.9-percent scale semispan wing in the Wichita State University 7x10-foot wind tunnel with simulated ice accretion shapes. Simulated ice shapes from large-droplet clouds, simple-geometry ice horn shapes, and simple-geometry spanwise ridge shapes typical of runback icing were tested. Three Reynolds number and Mach number combinations were tested over a range of angles of attack. Aerodynamic forces and moments were acquired from the tunnel balance and surface pressures and oil flow visualizations were acquired. This research supplements the Swept Wing Icing Program recently concluded by NASA, FAA, ONERA, and their partners by testing new ice shapes on the same wind tunnel model. Additional surface roughness was added to simulate large-droplet ice accretion aft of the highly three-dimensional primary ice shape, and it had little effect on the wing aerodynamic performance. Spanwise ridge simulations produced large increases in drag and small increases in maximum lift in most cases. Ridge size and location had significant effects on the performance and the lower-surface ridge was important contributing to the drag at low angle of attack and lift at high angle of attack due to the movement of the attachment line around the leading edge. Oil flow visualization and surface pressures help explain the spanwise effects on the flowfield and the resulting changes in lift and moment produced by the various ice shape simulations. Studies of a partial-span ridge simulating a residual icing case and additional simple horn cases to supplement SWIP data are also presented. The aerodynamic performance results from the simple horn ice cases are consistent with the previously identified trends in earlier studies with a more limited range of horn angles.