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Title:Large-scale swept-wing ice accretion modeling in the NASA Glenn Icing Research Tunnel using LEWICE3D
Author(s):Wiberg, Brock
Advisor(s):Bragg, Michael B.
Department / Program:Aerospace Engineering
Discipline:Aerospace Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):aircraft icing
ice shape
computational fluid dynamics (CFD)
aircraft certification
Abstract:The study of aircraft icing is necessary to ensure the safety of commercial, military, and general aviation aircraft. The certification of modern commercial transports requires manufacturers to demonstrate that these aircraft can safely operate during icing conditions consistent with the standards set forth by the Federal Aviation Administration (FAA). While some of these tests are performed on actual aircraft in flight, this is often very expensive and does not provide an adequately controlled matrix of test conditions. Computational tools are used throughout the design and certification of anti-ice systems. However, computational methods alone are not sufficient for aircraft certification. Icing wind tunnels are used for aircraft certification to reduce costs, provide a controlled test matrix of conditions, and validate computational icing tools. The size of aircraft models that can be tested in icing wind tunnels is limited by the size and capability of existing facilities. Large wings, such as those found on modern narrow and wide-body commercial transports, cannot fit in existing test sections without being dramatically scaled. Two methods of scaling exist. The first involves geometrically scaling a section of the reference wing to fit inside the tunnel test section and then scaling the icing conditions in order to maintain icing similitude. The second method maintains the full-scale leading edge of the reference geometry but replaces the aft section of the wing with a tail that is designed to produce similar flow around the leading edge but with a considerably shorter chord length, reducing model size and blockage. This type of model is called a hybrid and is used to generate full-scale ice shapes so that, in the simplest cases, no icing scaling is necessary. However, the methods can be combined so that the hybrid model design is used to maintain geometric similitude while icing scaling is employed to account for differences in pressure, velocity, or other conditions. Modern commercial transport aircraft have large, swept wings. While a broad set of experimental data exist in the literature for airfoil and straight wing icing, there is a distinct lack of data for large, swept wings. Such data is needed in order to better understand the 3D icing physics on swept wings and to allow computational tools to be developed and validated for 3D ice features such as scallops. In this thesis, computational tools were used to better understand the flow over a large-scale, swept-wing, hybrid model mounted vertically in the NASA Glenn Icing Research Tunnel (IRT). Fluent, a commercial CFD code, was used to calculate flows around the flapped-hybrid model in the IRT, mounted with the root at the floor and the tip at the ceiling of the test section. Inviscid analysis reveals that the upwash ahead of the model causes the local lift coefficient to increase significantly across the swept model due to the effect of the floor and ceiling. This change in spanwise loading is shown to move the attachment line location farther down the leading edge for stations on the model which are farther outboard. Two techniques for controlling this effect are explored. 1) A flap with three spanwise segments is shown to be ineffective in controlling the spanwise load distribution on the swept model with aspect ratio near unity. The effectiveness improves as aspect ratio is increased, but increasing the aspect ratio requires significant geometric scaling, resulting in limited applicability to large-scale models. 2) Twisting the model is shown to be an effective method of reducing the effective angle of attack across the model, compensating for the upwash and making the load distribution on the model more uniform. Twist adds complexity to the model and may not be necessary for producing quality ice shapes in the region of interest on the hybrid model, depending on the objectives of the research. LEWICE3D was used to simulate droplet impingement and ice accretion on the swept model in the IRT test section. Attachment line location is shown to be the primary driver of icing similarity. It is shown that on the flapped-hybrid model, the attachment line can be uniformly shifted on the leading edge by changing the angle of attack or flap deflection. This results in a range of angle of attack and flap angle combinations corresponding to a given attachment line location at the tunnel centerline. For a wind tunnel test at local elevation, it is shown that the heat transfer coefficient will by higher due to the increased density as compared to the in-flight icing conditions at altitude. A similitude method is applied to the hybrid model and the resulting ice shapes are compared. Finally, it is shown that for the droplet size considered, if the attachment line is matched, the model can be operated with the leading edge at an angle of attack other than that of the flight baseline and still produce ice shapes representative of the reference ice shapes generated on the baseline aircraft in free air. Operating at a higher angle of attack with lower flap angle is shown to reduce the overall model lift coefficient and the spanwise variation in attachment line position and, therefore, ice shape.
Issue Date:2014-01-16
Rights Information:Copyright 2013 Brock Wiberg
Date Available in IDEALS:2014-01-16
Date Deposited:2013-12

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