Michael B. Bragg

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

A 3D swept hybrid wing design method using hybrid airfoils is presented for the purpose of icing wind tunnel testing of large commercial aircraft. Hybrid airfoils are those that present the same leading-edge geometry of the full-scale aircraft wing with a redesigned truncated aft section, such that models can fit inside icing wind tunnels and still reproduce full-scale flowfield and ice accretion with reduced chord. The effects of tunnel sidewalls, model sweep angle, aspect ratio, and wind tunnel blockage are presented. Attachment line location is used as a first-order parameter for matching full-scale ice shapes, and methods for controlling its spanwise variation are assessed including the use of gap between model and tunnel wall, aerodynamic twist, and segmented flaps. Finally, model design tradeoffs are presented between competing performance parameters such as full-scale ice accretion agreement, wind tunnel load/speed limits, and model manufacturing/operational complexity.

Swept-Wing Ice Accretion Characterization and Aerodynamics

NASA, FAA, ONERA, the University of Illinois and Boeing have embarked on a significant, collaborative research effort to address the technical challenges associated with icing on large-scale, three-dimensional swept wings. The overall goal is to improve the fidelity of experimental and computational simulation methods for swept-wing ice accretion formation and resulting aerodynamic effect. A seven-phase research effort has been designed that incorporates ice-accretion and aerodynamic experiments and computational simulations. As the baseline, full-scale, swept-wing-reference geometry, this research will utilize the 65 percent scale Common Research Model configuration. Ice-accretion testing will be conducted in the NASA Icing Research Tunnel for three hybrid swept-wing models representing the 20, 64 and 83 percent semispan stations of the baseline-reference wing. Threedimensional measurement techniques are being developed and validated to document the experimental ice-accretion geometries. Artificial ice shapes of varying geometric fidelity will be developed for aerodynamic testing over a large Reynolds number range in the ONERA F1 pressurized wind tunnel and in a smaller-scale atmospheric wind tunnel. Concurrent research will be conducted to explore and further develop the use of computational simulation tools for ice accretion and aerodynamics on swept wings. The combined results of this research effort will result in an improved understanding of the ice formation and aerodynamic effects on swept wings. The purpose of this paper is to describe this research effort in more detail and report on the current results and status to date.

Computational and Experimental Ice Accretions of Large Swept Wings in the Icing Research Tunnel

A comparison of computational and experimental ice accretions is presented for three full-scale leading edge swept-wing models spanning from floor to ceiling in the NASA Glenn Icing Research Tunnel (IRT) at three different spanwise stations of the 65%-scale Common Research Model. Experimental ice shapes were generated on the leading edge of each model for a set of icing conditions, and then digitized with a 3D laser scanner. Computational simulations were done for the same flow and icing conditions of the experiment, utilizing CFD (OVERFLOW 3D RANS) for the flowfield solutions, and LEWICE3D for the 3D ice accretion calculations. Results showed both good ice accretion agreement and the need to further explore and better understand the complex 3D flowfield and ice accretion modeling.

Large-Scale Swept-Wing Icing Simulations in the NASA Glenn Icing Research Tunnel Using LEWICE3D

Computational icing simulations of a hybrid, swept-wing model in the NASA IRT are presented. The results of these simulations are compared to those for the same icing conditions conducted on the full-scale reference wing. The effects of tunnel sidewalls, attachment line position, and altitude are considered. A discussion of icing scaling and the results of one scaling approach are given. The variation of impingement and ice shape with span in the tunnel for different angles of attack and flap deflection are presented.

Characterization of low-frequency oscillations in the flowfield about an iced airfoil

Wind-tunnel measurements were used to identify and characterize the low-frequency oscillation present in the flowfield about an NACA 0012 airfoil with a horn-ice shape. This low-frequency mode was identified in the unsteady content of the airfoil lift coefficient and the corresponding Strouhal numbers compared well with those reported in the literature. To study the relationship between the ice-induced separation bubble dynamics and the airfoil circulation, the unsteady shear-layer reattachment location was determined using measurements from a surface-mounted hot-film array. At the low-frequency mode, the lift coefficient led the reattachment location by a phase of π/2. Additional characterization of the relationship between the unsteady shear-layer reattachment location and the unsteady airfoil pressure distribution was also completed, along with an analysis of the convective qualities of the low-frequency oscillation throughout the airfoil pressure distribution.

Effect of Ice Shape Fidelity on Swept-Wing Aerodynamic Performance

Low-Reynolds number testing was conducted at the 7 ft x 10 ft Walter H. Beech Memorial Wind Tunnel at Wichita State University to study the aerodynamic effects of ice shapes on a swept wing. A total of 17 ice shape configurations of varying geometric detail were tested. Simplified versions of an ice shape may help improve current ice accretion simulation methods and therefore aircraft design, certification, and testing. For each configuration, surface pressure, force balance, and fluorescent mini-tuft data were collected and for a selected subset of configurations oil-flow visualization and wake survey data were collected. A comparison of two ice shape geometries and two configurations with simplified geometric detail for each ice shape geometry is presented in this paper.

Unsteady modes in flowfield about airfoil with horn-ice shape

An experimental investigation was conducted on an NACA 0012 airfoil with a leading-edge horn-ice shape to identify and characterize flowfield unsteadiness related to ice-induced flow separation. This type of iced-airfoil flowfield was dominated by a leading-edge separation bubble, which is associated with several inherent modes of unsteadiness. Using unsteady surface pressure and wake velocity measurements, three distinct modes of unsteadiness were identified at various locations throughout the flowfield. These unsteady modes included a regular mode of vortical motion and a shear-layer flapping mode, which are both associated with separation bubbles. A low-frequency mode that was associated with the thin-airfoil stall type of the iced airfoil was also observed and was represented by a global oscillation of the airfoil circulation. The characteristic frequencies and flowfield locations corresponding to these unsteady modes were compared with those reported in the literature for iced-airfoil flowfields and ...

Generation of Fullspan Leading-Edge 3D Ice Shapes for Swept-Wing Aerodynamic Testing

The deleterious effect of ice accretion on aircraft is often assessed through dry-air flight and wind tunnel testing with artificial ice shapes. This paper describes a method to create fullspan swept-wing artificial ice shapes from partial span ice segments acquired in the NASA Glenn Icing Reserch Tunnel for aerodynamic wind-tunnel testing. Full-scale ice accretion segments were laser scanned from the Inboard, Midspan, and Outboard wing station models of the 65% scale Common Research Model (CRM65) aircraft configuration. These were interpolated and extrapolated using a weighted averaging method to generate fullspan ice shapes from the root to the tip of the CRM65 wing. The results showed that this interpolation method was able to preserve many of the highly three dimensional features typically found on swept-wing ice accretions. The interpolated fullspan ice shapes were then scaled to fit the leading edge of a 8.9% scale version of the CRM65 wing for aerodynamic wind-tunnel testing. Reduced fidelity versions of the fullspan ice shapes were also created where most of the local three-dimensional features were removed. The fullspan artificial ice shapes and the reduced fidelity versions were manufactured using stereolithography.

Summary of Ice Shape Geometric Fidelity Studies on an Iced Swept Wing

Understanding the aerodynamic impact of swept-wing ice accretions is a crucial component of the design of modern aircraft. Computer-simulation tools are commonly used to approximate ice shapes, so the necessary level of detail or fidelity of those simulated ice shapes must be understood relative to high-fidelity representations of the ice. Previous tests were performed in the NASA Icing Research Tunnel to acquire high-fidelity ice shapes. Some of those ice shapes are based on aircraft certification requirements. From this database, full-span artificial ice shapes were designed and manufactured for both an 8.9%-scale and 13.3%-scale semispan wing model of the CRM65 which has been established as the full-scale baseline for this sweptwing project. These models were tested in the Walter H. Beech wind tunnel at Wichita State University and at the ONERA F1 facility, respectively. The data collected in the Wichita St. University wind tunnel provided a low-Reynolds number baseline study while the pressurized F1 facility produced data over a wide range of Reynolds and Mach numbers with the highest Reynolds number studied being approximately Re = 11.9×10. Three different fidelity representations were created based on three different icing conditions. Lower-fidelity ice shapes were created by lofting a smooth ice shape between cross-section cuts of the high-fidelity ice shape. Grit roughness was 1 Research Associate, Dept. of Aerospace Engineering, 306 Talbot Lab, 104 S. Wright St., Member AIAA. 2 Research Aerospace Engineer, Icing Branch, 21000 Brookpark Rd., MS 11-2, Associate Fellow AIAA. 3 Engineer V, Icing Branch, 21000 Brookpark Rd., MS 11-2, Senior Member AIAA. 4 Research Assistant Professor, William E. Boeing Department of Aeronautics and Astronautics, Guggenheim Hall Room 211, Box 352400, Member AIAA. 5 Frank and Julie Jungers Dean, College of Engineering, and Professor, William E. Boeing Department of Aeronautics and Astronautics, University of Washington; Loew Hall Room 371, Box 352180, AIAA fellow. https://ntrs.nasa.gov/search.jsp?R=2018000676

Effect of Simulated Scalloped Ice on the Aerodynamics of a Swept-Wing at Low-Reynolds Number [STUB]

Research Assistant, William E. Boeing Department of Aeronautics and Astronautics; Guggenheim Hall Room 211, Box 352400, Seattle, WA 98195-2400, AIAA student member. † Visiting Professor, William E. Boeing Department of Aeronautics and Astronautics; Guggenheim Hall Room 211, Box 352400, Seattle, WA 98195-2400. ‡ Frank and Julie Jungers Dean, College of Engineering, and Professor, William E. Boeing Department of Aeronautics and Astronautics; Loew Hall Room 371, Box 352180, Seattle, WA 98195-2180, AIAA fellow. § Research Assistant Professor, William E. Boeing Department of Aeronautics and Astronautics; Guggenheim Hall Room 211, Box 352400, Seattle, WA 98195-2400, AIAA member. ¶ Research Associate, Department of Aerospace Engineering, 306 Talbot Lab, 104 S. Wright St., AIAA member. # Research Aerospace Engineer, Icing Branch, 21000 Brookpark Rd., Associate Fellow AIAA. ** Research Engineer, Icing Branch, 21000 Brookpark Rd., Senior Member AIAA. Effect of Simulated Scalloped Ice on the Aerodynamics of a Swept-Wing at Low-Reynolds Number