Effect of Geometric Fidelity on the Aerodynamics of a Swept Wing with Glaze Ice Accretion

Aerodynamic assessment of icing effects on swept wings is an important component of a larger effort to improve three-dimensional icing simulation capabilities. An understanding of ice-shape geometric fidelity on iced-wing aerodynamics and the associated flowfield features are needed to guide the development and validation of ice-accretion simulation tools. To this end, wind-tunnel testing was carried out for 8.9% and 13.3% scale semispan wing models based upon the Common Research Model airplane configuration. Various levels of geometric fidelity of an artificial ice shape representing a glaze-ice accretion on a swept wing were investigated. The highest fidelity artificial ice shape reproduced all of the three-dimensional features associated with the glaze ice accretion. The lowest fidelity artificial ice shapes were simple, spanwise-varying horn ice geometries intended to represent the maximum ice thickness on the wing upper surface. The results presented in this paper show that the addition of grit roughness to some lower-fidelity artificial ice shapes resulted in favorable lift and pitching moment comparisons to the wing with the highest fidelity artificial ice shape. In the range of 4.3 to 7.4 deg. angle of attack, surface oil flow visualization and pressure data show that the wing with the two lower fidelity simulations clearly demonstrated a leading edge vortex dominated flowfield, referred to as type I. For the wing with the high fidelity ice shape, the flowfield at lower angles of attack was characterized by streamwise-running, counter-rotating vortical flow referred to as type II. Between 6.4 and 7.4 deg. angle of attack, the effect of the type II flow structures was significantly altered and gave way to the type I leading edge vortex. This means that for angles of attack 7.4 deg. and higher, the wing with all three configurations exhibited the same type of flowfield. This helps to explain why there is reasonably good agreement in the lift and pitching moment coefficients among these configurations.