No abstract

No abstract

No abstract

Results are presented of an experimental study designed to characterize and evaluate the aerodynamic performance penalties of residual and intercycle ice accretions that result from the cyclic operation of a typical aircraft deicing system. Icing wind-tunnel tests were carried out on a 36-in. chord NACA 23012 airfoil section equipped with a pneumatic deicer for several different Federal Air Regulation 25 Appendix C cloud conditions. Results from the icing tests showed that the intercycle ice accretions were much more severe in terms of size and shape than the residual ice accretions. Molds of selected intercycle ice shapes were made and converted to castings that were attached to the leading edge of a 36-in. chord NACA 23012 airfoil model for aerodynamic testing. The aerodynamic testing revealed that the intercycle ice shapes caused a significant performance degradation. Maximum lift coefficients were typically reduced about 60% from 1.8 (clean) to 0.7 (iced) and stall angles were reduced from 17 deg (clean) to 9 deg (iced). Changes in the Reynolds number (from 2.0 × × 10 6 to 10.5 × × 10 6) and Mach number (from 0.10 to 0.28) did not significantly affect the iced-airfoil performance. Nomenclature C d = drag coefficient C l = lift coefficient C l,max = maximum lift coefficient, coincident with α stall C l,α = lift-curve slope C m = quarter-chord pitching-moment coefficient c = airfoil chord length k = ice-roughness height or thickness M = freestream Mach number Re = Reynolds number based on chord x = chordwise position along airfoil y = normal position from airfoil chord line α = airfoil angle of attack α stall = stalling angle of attack, coincident with C l,max

Recent investigations of two-dimensional airfoil stalling characteristics have revealed low-frequency and highly unsteady ow in some cases and large-scale three-dimensional structures in other cases. The latter were referred to as "stall cells" and can form on two-dimensional con gurations where the ends of the airfoil model are ush with tunnel side walls or end plates. This paper presents results of detailed investigations of the stalling characteristics of several airfoils that exhibited both low-frequency unsteadiness and large-scale three-dimensional structures. The airfoils were wind-tunnel tested in a two-dimensional con guration. The primary measurements were spanwise wake velocity and mini-tuft ow visualization. The results showed that airfoils with trailing-edge separations at and above maximum lift (static stall) exhibited stall-cell patterns. Conversely, airfoils that had leading-edge separation bubbles that grew in size as the angle of attack was increased into stall developed the low-frequency, highly unsteady ow. This unsteadiness was found to be essentially two dimensional. Therefore, the development of either of these phenomena appears to be determined by the characteristics of the boundary-layerseparation leading up to the stall.

No abstract

are conducting a major research program whose goal is to improve our understanding of the aerodynamic scaling of ice accretions on airfoils. The program when it is completed will result in validated scaled simulation methods that produce the essential aerodynamic features of the full-scale iced-airfoil. This research will provide some of the first, high-fidelity, full-scale, iced-airfoil aerodynamic data. An initial study classified ice accretions based on their aerodynamics into four types: roughness, streamwise ice, horn ice, and spanwise-ridge ice. Subscale testing using a NACA 23012 airfoil was performed in the NASA IRT and University of Illinois wind tunnel to better understand the aerodynamics of these ice types and to test various levels of ice simulation fidelity. These studies are briefly reviewed here and have been presented in more detail in other papers. Based on these results, full-scale testing at the ONERA F1 tunnel using cast ice shapes obtained from molds taken in the IRT will provide full-scale iced airfoil data from full-scale ice accretions. Using these data as a baseline, the final step is to validate the simulation methods in scale in the Illinois wind tunnel. Computational ice accretion methods including LEWICE and ONICE have been used to guide the experiments and are briefly described and results shown. When full-scale and simulation aerodynamic results are available, these data will be used to further develop computational tools. Thus the purpose of the paper is to present an overview of the program and key results to date.

This paper discusses the use of several experimental techniques to investigate the performance and flowfield of a swept wing with leading-edge ice at low Reynolds numbers. Force balance measurements were made over a range of angles of attack and Reynolds numbers. Surface oil visualization and pressure sensitive paint were used to investigate the flow over the surface of the wing, while five-hole probe wake surveys were used to investigate the wake. The flowfield of the iced swept wing was dominated by a leading-edge vortex that formed at low angles of attack due to separation from the tip of the ice shape, while for the clean wing a vortex did not form until higher angles of attack. The effect of Reynolds number on the performance and flowfield was also investigated.