Simulation of Residual and Intercycle Ice Shapes Using Step Ice and Roughness

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Experiments were performed with a laminar flow wing equipped with a full span control surface to evaluate the effect of a range of simulated ice shapes on wing aerodynamic performance. The tests were conducted in the 7-ft by 10-ft wind tunnel facility at Wichita State University at airspeed of 100 mph, geometric angles of attack from -8° to +23°, Mach number of 0.134 and a Reynolds number of 3.80 million based on the mean aerodynamic chord. During the aerodynamic tests, six component force and moment measurements, control surface hinge moments and surface pressures at two spanwise stations were obtained. Simulated ice shapes tested included residual and intercycle ice shapes defined from icing tunnel tests with a mechanical deicing system installed in the wing leading edge. Full span step ice shapes simulated with quarter-rounds with heights of 2 mm and 4 mm were also tested at 1%, 3%, 5% and 8% chord to assess step ice location on aerodynamic performance. In addition, the 4-mm step ice shape was tested with sandpaper roughness of 24-grit, 40-grit and 80-grit upstream and also downstream of the step to help quantify the effect of roughness often observed with residual and intercycle ice shapes. In general, wing aerodynamic performance exhibited considerable sensitivity to ice shape configuration. The reduction in clean wing CL,stall due to the 18 simulated ice shapes tested ranged from 8.9% to 22.9% while the increase in wing CD,min ranged from 0% to 74.3%. The largest reduction in CL,stall was obtained with the 4-mm step ice at 1% chord on the wing upper surface combined with 24-grit roughness from approximately 1% to 20% chord on the upper surface. The largest increase in CD,min occurred with the 4-mm step ice at 1% chord on the wing upper surface with leading edge roughness of 24-grit extending from 1% chord on the upper surface to 1% chord on the lower surface. The simulated residual and intercycle ice shapes tested reduced clean wing CL,stall by 11.5% to 16.6%, increased clean wing CD,min by 35.0% to 49.5% and resulted in more negative pitching moments about the wing aerodynamic center. Their effect on control surface hinge moments was small. Computational fluid dynamic analysis was also performed for the wing model with the 4-mm step ice, combinations of 4mm step ice and roughness, and a simulated intercycle ice shape. The tunnel walls were included in the flow simulations performed. The analysis was performed at a geometric angle of attack of approximately 7° and airspeed of 100 mph. Overall, the agreement between analysis and experiment was good for the clean and iced wing configurations computed.