Sensitivity of Aircraft Performance to Icing Parameter Variations

A IRCRAFT icing is widely recognized as a significant hazard to aircraft operations. For this reason, aircraft and ice protection systems must be certified for flight into icing conditions. The aircraft certification and icing research communities rely on icing wind tunnels as an efficient way to produce ice accretions in a controlled environment. The aerodynamic performance of aircraft with these ice accretions contributes to the certification of aircraft. It is therefore critical to ensure that the ice accretions are simulated within a known aerodynamic uncertainty. The aerodynamic performance of an airfoil containing an ice accretion is highly dependent on the geometry of the ice accretion, which is in turn dependent on icing conditions such as temperature, liquid water content (LWC), and median volume diameter (MVD). Icing wind tunnels have the capability to vary LWC and MVD, however, the accuracy in LWC and MVD required to create an aerodynamically representative ice accretion is not known. This research addressed the problem of “how good is good enough” by determining the relationship and sensitivity of iced-airfoil performance to these icing cloud parameters. In addition, these data were placed in perspective by relating measurable or significant aircraft performance changes to the underlying changes in airfoil aerodynamic performance. Recent NASA studies [1,2] in the Icing Research Tunnel (IRT) measured the effect of icing parameter variations on ice-accretion geometry. These studies showed that small variations in LWC and MVD corresponded to distinct changes in ice-accretion geometry. In addition, the effect of ice-accretion geometry on aerodynamic performance has been recently investigated [3–6]. Papadakis et al. [3,4] used spoilers to simulate horn ice and showed that Clmax degradation was related to the horn height (k=c). Kim and Bragg [5], and Broeren et al. [6] showed that k=c and surface location (s=c) had the biggest impact on airfoil performance degradation. This study used ice tracings from theNASA studies [1,2] as a basis to examine the sensitivity of aerodynamic performance to icing parameter variations. Eleven ice-accretion tracings were selected from the 39measured byMiller et al. [2] to reasonably span the range of LWC andMVD tested. The selected ice tracings were modeled as two-dimensional smooth simulated ice shapes for wind-tunnel testing. The experiments for this research were performed in the Illinois subsonic, low-turbulence, open-return wind tunnel. The airfoil model was an aluminum NACA 0012 airfoil with an 18 in. chord, 33.6 in. span, and a removable leading edge to facilitate installation of the ice simulations. Testing was performed at a Reynolds number of 1.8 million, and a Mach number of 0.18. The results of the aerodynamic testing were related to the corresponding icing parameters in the form of two sensitivities: airfoil performance to icing parameter variations, and derived aircraft performance to icing parameter variations. More details can be found in Campbell et al. [7,8].