Aerodynamic Simulation of Runback Ice Accretion

Abstract

This paper presents the results of recent investigations into the aerodynamics of simulated runback ice accretion on airfoils. Aerodynamic testing was performed on a full-scale, 72-in.-chord (1828.8-mm-chord), NACA 23012 airfoil model over a Reynolds number range of 4:7 10 6 to 16:0 10 6 and a Mach number range of 0.10 to 0.28. A high-fidelity ice-casting simulation of a runback ice accretion was attached to the model leading edge. For Re ˆ 16:0 10 6 and M ˆ 0:20, the artificial ice shape decreased the maximum lift coefficient from 1.82 to 1.51 and decreased the stalling angle of attack from 18.1 to 15.0 deg. In general, the iced-airfoil performance was insensitive to Reynolds and Mach number changes over the range tested. Aerodynamic testing was also conducted on a quarter-scale NACA 23012 model [18 in. (457.2 mm) chord] at Re ˆ 1:8 10 6 and M ˆ 0:18, using low-fidelity geometrically scaled simulations of the full-scale casting. It was found that simple two-dimensional simulations of the upper-and lower-surface runback ridges provided the best representation of the full-scale, high-Reynolds-number, iced-airfoil aerodynamics. Higher-fidelity simulations of the runback ice accretion that included geometrically scaled three-dimensional features resulted in larger performance degradations than those measured on the full-scale model. Based upon this research, a new subclassification of spanwise-ridge ice is proposed that distinguishes between short and tall ridges. This distinction is made in terms of the fundamental aerodynamic characteristics as described in this paper. Nomenclature C d = drag coefficient C l = lift coefficient C l;max = maximum lift coefficient, coincident with stall C l; = lift-curve slope C m = quarter-chord pitching-moment coefficient c = airfoil chord length k = ice-roughness height or thickness M = freestream Mach number n = wall-normal distance above airfoil surface Re = Reynolds number based on chord U = mean streamwise velocity U 1 = freestream velocity u RMS = root-mean-square of fluctuating streamwise velocity x = chordwise position along airfoil y = normal position from airfoil chord line = airfoil angle of attack stall = stalling angle of attack, coincident with C l;max C d;rms = percent root-mean-square difference in C d

Experimental Study of Full-Scale Iced Airfoil Aerodynamic Performance Using Sub-Scale Simulations

“…The boundary-layer scaled geometries were much larger than the geometrically-scaled geometries and tended to cause increased aerodynamic penalties relative to those of the geometrically-scaled simulations. Broeren et al 15 showed that the geometrically-scaled simulations were likely already too conservative and that other scaling methods may be necessary to appropriately scale ice geometries which have heights that may be on the order of the local boundary-layer thickness at relevant lift coefficients.…”

“…As discussed in Chapter 2, Broeren et al 15 sub-classified spanwise ridges into two categories based on their key aerodynamic characteristics: tall ridges, which generate a long separation bubble; and short ridges, which generate a short separation bubble. Each type of ridge was simulated in this study.…”

“…Usually the airfoil leading edge is free or mostly free of ice, and a relatively two-dimensional ridge forms downstream of the heated porion of the leading edge. Broeren et al 15 sub-classified spanwise ridges based on the types of flowfield they generate as either tall or short. Tall ridges generate long separation bubbles which have a global effect on the airfoil C p distribution, while short ridges generate short separation bubbles which have only a local effect on the airfoil C p distribution.…”

“…Broeren et al 9,15 measured the aerodynamic performance degradation of a 72-inch chord NACA 23012 airfoil using high-fidelity, full-scale ice castings representative of each type of iced-airfoil flowfield at near-flight Reynolds numbers. Representative data from this testing are shown in Fig.…”

“…This phenomenon has been observed for other types of ice accretion as well, such as spanwise-ridge ice. 15 To isolate the effects of surface roughness, many studies have compared identical 2-D simulations of horn-ice with and without roughness and documented its effect. In these studies the presence of surface roughness had differing effects.…”