A Hybrid Airfoil Design Method for Icing Wind Tunnel Tests

Abstract

Modern commercial aircraft wings are far too large to be tested full-scale in existing icing wind tunnels and ice accretion scaling methods are not practical for large scale factors. Thus the use of hybrid scaling techniques, maintaining full-scale leading-edges and redesigned aft sections, is an attractive option for generating full-scale leading-edge ice accretions. The advantage lies in utilizing reduced chord models that minimize blockage effects in the icing tunnels. The present work discusses the design of hybrid airfoils with large scale factors that match the ice shapes of the full-scale airfoils predicted by LEWICE. Assessments of the effects of scale factor, extent of the full-scale leading-edge, nose droop angle, zero-angle of attack pitching moment coefficient (C m0 ), and droplet size are also presented. Hybrid or truncated airfoils are shown to produce ice shapes accurately, even at angles of attack different from the design angle of attack with the proper application of either flap, adjusted test angle of attack, or both. Further results suggest that hybrid circulation does not need to match full-scale circulation in order to match ice shapes, resulting in decreased loading for higher scale factor hybrid airfoils. Matching the flowfield around the hybrid airfoil to the full-scale flowfield provided a superior method for predicting ice shape agreement, stagnation point location being a first order and suction peak magnitude a second order parameter. This goal can be accomplished by varying the aft geometry, through C m0 and nose droop angle.Downloaded by UNIVERSITY OF ILLINOIS on August 14, 2013 | http://arc.aiaa.org |

3D Swept Hybrid Wing Design Method for Icing Wind Tunnel Tests

“…The cases requiring the attachment line location to be farthest down the leading edge are considered the most aggressive scenarios because they require the largest circulation, and therefore, impose the highest risk of flow separation to the hybrid wing. Fujiwara et al 12 show in the 2D hybrid airfoil design method that there is no unique combination of angle of attack and flap deflection that reaches a particular stagnation point location. Instead, there is one corresponding flap deflection for each angle of attack that reaches the same stagnation point location, with very distinct loads.…”

“…The hybrid wing design starts with the design of a 2D hybrid airfoil from a normal cut of the full-scale airfoil of the CRM65 to match the stagnation point location for that full-scale airfoil cut. The details and design tradeoffs of this first step are well described by Fujiwara et al 12 In order to properly represent a swept wing in 2D with simple sweep theory, 37 the hybrid airfoil is designed for a full-scale airfoil that is cut in the direction normal to the leading edge of the full-scale wing.…”

“…Fujiwara et al 12 showed that running the same hybrid airfoil at higher angles of attack with lower flap deflections or even no flaps while reaching the same stagnation point locations leads to similar ice shapes, with a lower load. A similar study is done by Wiberg et al 17 , running the model at higher angles of attack without the flap, while maintaining the same attachment line location at tunnel centerline.…”

“…Values of γ can be either positive or negative, while C m0 is usually negative. 35,36 A more detailed discussion on the 2D hybrid airfoil design method is presented by Fujiwara et al, 12 where matching stagnation point location is shown to be of first order for matching full-scale ice shapes.…”

“…A design method for a straight, untapered hybrid wing can be as straight forward as the extrusion of a hybrid airfoil, whose design method is well documented by Saeed et al 11 and further explored by Fujiwara et al 12 A broad set of experimental data is available in the literature under airfoil and straight wing icing. The design of a swept, hybrid wing, on the other hand, introduces design challenges related to the three-dimensionality of swept wing flowfields 13 and ice shapes, 14 for which there is a lack of experimental data.…”