Wind tunnel tests were performed on an 8.9-percent scale semispan wing in the Wichita State University 7x10-foot wind tunnel with simulated ice accretion shapes. Simulated ice shapes from large-droplet clouds, simple-geometry ice horn shapes, and simple-geometry spanwise ridge shapes typical of runback icing were tested. Three Reynolds number and Mach number combinations were tested over a range of angles of attack. Aerodynamic forces and moments were acquired from the tunnel balance and surface pressures and oil flow visualizations were acquired. This research supplements the Swept Wing Icing Program recently concluded by NASA, FAA, ONERA, and their partners by testing new ice shapes on the same wind tunnel model. Additional surface roughness was added to simulate large-droplet ice accretion aft of the highly three-dimensional primary ice shape, and it had little effect on the wing aerodynamic performance. Spanwise ridge simulations produced large increases in drag and small increases in maximum lift in most cases. Ridge size and location had significant effects on the performance and the lower-surface ridge was important contributing to the drag at low angle of attack and lift at high angle of attack due to the movement of the attachment line around the leading edge. Oil flow visualization and surface pressures help explain the spanwise effects on the flowfield and the resulting changes in lift and moment produced by the various ice shape simulations. Studies of a partial-span ridge simulating a residual icing case and additional simple horn cases to supplement SWIP data are also presented. The aerodynamic performance results from the simple horn ice cases are consistent with the previously identified trends in earlier studies with a more limited range of horn angles.

An experimental study of a swept flat plate has been performed in the University of Washington 3’ by 3’ Low-Speed Wind Tunnel to improve the understanding of iced swept-wing flowfields. The swept flat plate model included two interchangeable backward-facing steps that were mounted to the full span of the plate leading edge, as well as an adjustable trailing-edge flap. Each of the steps was designed to recreate one of two key flowfields characteristic of swept wings with artificial ice shapes while reducing the geometric complexity relative to the swept-wing model. The first was a spanwise-running leading-edge vortex produced by certain low-fidelity artificial ice shapes. This type of flowfield is referred to as Type I, and was produced using the solid backward-facing step. Characteristic streamwise-running streaks of oil identify the second flowfield in surface flow visualization. This flow pattern was referred to as Type II, and was recreated with a modified backward-facing step that included spanwise-periodic gaps. Configurations of the flat plate were tested at four trailing-edge flap settings at a Reynolds number based on step height of 5.03 × 10^4 , which corresponds to a Mach number of 0.176. The experimental techniques used included fluorescent-oil surface flow visualization, surface pressure measurements, and five-hole pressure probe measurements. Two tentative categories of Type II flowfield features were identified. In the first category, referred to as “vortex generator type,” each Type II flowfield feature was correlated to a single discontinuity in the step. Flow visualization showed that these are likely the result of counter-rotating vorticity that forms in wakes of each solid feature in the discontinuous step. In the second category, referred to as “shear layer instability-type,” Type II features did not correspond to a single discontinuity. This behavior may be attributed to the discontinuities exciting an instability in the separated shear layer, or streamwise vorticity coalescing off of the flat plate surface.

Understanding the aerodynamic impact of swept-wing ice accretions is a crucial component of modern aircraft design. Ice-accretion simulation tools are commonly utilized in the design process, but the necessary geometric fidelity of the ice shapes generated by those codes is not fully understood. Assessment of the iced-wing aerodynamics and associated flowfields can provide some guidance regarding the impact of different geometric-fidelity ice-shape representations. Previous tests were performed in the NASA Icing Research Tunnel to acquire high-fidelity ice shapes. From this database, full-span artificial ice shapes were designed and manufactured for a subscale wind-tunnel model based on the Common Research Model. This work investigates the flowfield associated one type of low-fidelity representation of a swept wing with scalloped ice accretion. In an attempt to quantify the aerodynamic impact of the highly three-dimensional features in the high-fidelity ice shape, discontinuities were introduced into a smoothed version of the high fidelity ice shape. Both the spacing between the discontinuities and the angle of cutting plane used for creating the discontinuities were investigated. Comparisons are made between the wing with these 3D discontinuous ice shapes as compared to the high-fidelity case by examining surface oil flow visualization and surface pressure data in addition to the standard aerodynamic performance parameters. At angles of attack less than approximately 6 deg., the flowfield on the wing appears similar between the 3D discontinuous configurations and the high fidelity case. Streamwise streak features dominate the surface flow. As the angle of attack increases, these flow features remain the dominant feature for the high fidelity configuration relative to any of the 3D discontinuous ones. The flowfield on the wing with the high fidelity ice shape transitions to a flow dominated by a spanwise leading-edge vortex as the angle of attack increases further. Some of the 3D discontinuous configurations do result in a similar flowfield at approximately 10 deg. angle of attack, but others never resulted in a similar flowfield. A close inspection of the flowfields shows that none of the 3D discontinuous configurations results in a flowfield consistently similar to the high fidelity configuration across a range of angles of attack. The complex flowfield associated with a swept wing with a highly three dimensional scalloped ice accretion cannot be reproduced simply by replacing that ice shape with a smooth ice shape made artificially discontinuous.

Aerodynamic assessment of icing effects on swept wings is an important component of a larger effort to improve three-dimensional icing simulation capabilities. An understanding of ice-shape geometric fidelity on iced-wing aerodynamics and the associated flowfield features are needed to guide the development and validation of ice-accretion simulation tools. To this end, wind-tunnel testing was carried out for 8.9% and 13.3% scale semispan wing models based upon the Common Research Model airplane configuration. Various levels of geometric fidelity of an artificial ice shape representing a glaze-ice accretion on a swept wing were investigated. The highest fidelity artificial ice shape reproduced all of the three-dimensional features associated with the glaze ice accretion. The lowest fidelity artificial ice shapes were simple, spanwise-varying horn ice geometries intended to represent the maximum ice thickness on the wing upper surface. The results presented in this paper show that the addition of grit roughness to some lower-fidelity artificial ice shapes resulted in favorable lift and pitching moment comparisons to the wing with the highest fidelity artificial ice shape. In the range of 4.3 to 7.4 deg. angle of attack, surface oil flow visualization and pressure data show that the wing with the two lower fidelity simulations clearly demonstrated a leading edge vortex dominated flowfield, referred to as type I. For the wing with the high fidelity ice shape, the flowfield at lower angles of attack was characterized by streamwise vorticity flow referred to as type II. Between 6.4 and 7.4 deg. angle of attack, the type II flow structures was significantly altered and gave way to the type I leading edge vortex. This means that for angles of attack 7.4 deg. and higher, the wing with all three configurations exhibited the same type of flowfield. This helps to explain why there is reasonably good agreement in the lift and pitching moment coefficients among these configurations.

The effect of geometric fidelity on the aerodynamics of a swept wing with a “scallop” ice shape was studied. Three geometric fidelity versions of the ice shape were studied. The High Fidelity ice shape maintained all of the highly 3D features of the scallop shape. The 3D Smooth ice shape was smoothly lofted over the High Fidelity shape in order to eliminate all of the local 3D feature. The third ice shape was the 3D Smooth ice shape with roughness grit attached to the surface. The two 3D Smooth versions of the ice shape exhibited a flowfield characterized by a leading edge separation bubble that rolled into a spanwise running vortex. The surface pressure data showed classic leading edge separation bubbles that are observed on 2D airfoils with leading edge horn ice shapes. The High Fidelity ice shape exhibited a flowfield characterized by streamwise vortices that formed downstream of the ice shape. The streamwise vortices observed downstream of the High Fidelity ice shape appeared to reduce the size of the separation suction peak observed downstream of the 3D Smooth ice shapes. This reduced the lift for the High Fidelity ice shape, when compared to the 3D Smooth ice shapes. However, these streamwise vortices may have allowed the flow to remain attached longer and slightly increased the stall angle of attack, even though the maximum lift was lower.

An important consideration for swept-wing ice shapes is the level of geometric fidelity required to accurately capture the aerodynamics. One way to help make the task of addressing this more manageable is to organize the ice shapes into a small number of classifications. These classifications are done by grouping similar ice shape geometries that also have similar iced wing aerodynamics. Ice shape classifications for airfoils are more mature and are reviewed as an example. Swept wing ice shape classifications are based on the well-established airfoil classifications and here five classifications are proposed: leading-edge roughness, streamwise ice, 3D leading-edge horn, highly 3D leading-edge horn and spanwise ridge. Recent data on swept wing icing aerodynamics is used to develop and support this classification. The development, or suppression, of the leading-edge separation vortex on swept wings without a leading-edge device is seen to be key in the classification of the highly 3D leading-edge horn.

A comparison of computational and experimental ice accretions generated on three swept-wing models in the NASA Glenn Icing Research Tunnel is presented. The wind tunnel models span floor to ceiling and present the same full-scale leading edges of three different spanwise wing stations of the 65%-scale modern commercial aircraft known as the Common Research Model. Experimental ice shapes were generated on the leading edge of each model for a set of icing conditions and digitized with a three-dimensional (3-D) laser scanner, representing the ice accretions that would be obtained at their corresponding stations on the full-scale wing. Computational ice shapes were generated on the same wind tunnel models at the same flow and icing conditions of the experiment, using 3-D Reynolds-averaged Navier-Stokes computational fluid dynamics code OVERFLOW for the flowfield, and LEWICE3D for the 3-D ice-accretion simulations. Results show large swept-wing ice accretions from high-quality experiments and state-of-the-art ice-accretion computational tools. The comparison between experiments and numerical simulations demonstrates the capabilities and limitations of the current computational tools in modeling the physics of complex 3-D flowfield and ice accretion, and indicates the need for further development and research exploration.

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. 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 swept-wing 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 = 11.9×106. Past work focused on only three different fidelity variations for ice shapes based on multiple icing conditions. This work presents a more detailed investigation into several fidelity representations of a single highly three-dimensional scallop ice accretion. Sensitivity to roughness size and application technique on a low-fidelity smooth ice shape is described. The data indicate that the aerodynamic performance is not especially sensitive to the grit variations. An ice accretion code was also used to generate ice shapes for aerodynamic testing and comparisons. These ice shapes have a general appearance like the low-fidelity smooth ice shapes, but in this case, the computer-generated ice shape is significantly smaller. As such, the impact of that ice shape on the aerodynamic performance of the wing is reduced compared to the smooth ice shape based on the icing experiment for those same conditions. Spanwise discontinuities were also introduced to a low-fidelity ice shape in an attempt to quantify the impact of those variation in the high-fidelity ice shape. While the lift data indicate good agreement between the high-fidelity ice shapes and the low-fidelity ice shapes with spanwise discontinuities, a closer investigation of the data suggests potential, significant differences in the flowfield. These results were similar at both facilities over the wide range of test conditions utilized.

The certification of modern commercial aircraft requires manufacturers to demonstrate flight safety under various scenarios, including icing conditions. Although computational tools play a key role in icing-related aircraft design and certification, icing wind-tunnel testing remains an important part of the process. The size of models that can be tested is limited by the dimensions of the existing icing wind-tunnel facilities. To obtain ice accretions on full-scale aircraft wings in icing wind tunnels, scaling methods must be applied. One attractive option is the use of hybrid airfoils. Hybrid airfoils present the same leading-edge geometry of the full-scale airfoil but replace the aft section with a redesigned geometry of reduced chord. When properly designed, these models generate the full-scale ice accretion on the leading edge, with reduced blockage and aerodynamic loads. This paper presents an investigation of the effects of different design parameters on the performance of hybrid airfoils, identifies the key design parameters to generate full-scale ice shapes, and puts the research findings in perspective with overall model design tradeoffs.

Hybrid-wing models are those that present the same leading-edge geometry of the full-scale aircraft wing and a redesigned aft section of reduced chord, such that models can be tested inside an icing wind tunnel. When properly designed, these models reproduce the full-scale flowfield and ice accretions on the leading edge, with reduced tunnel blockage. Although a method exists for designing hybrid airfoils, no systematic method is available in the literature for designing hybrid swept wings. This paper presents a method for designing three-dimensional swept hybrid wings using hybrid airfoils for the purpose of generating full-scale ice accretions, such as those on large commercial aircraft, in icing wind tunnels. An application example using the method is shown for the design of three hybrid wings representing different wing stations of a modern commercial aircraft. Investigations of the effects of tunnel walls, model sweep angle, model aspect ratio, model thickness, and wind-tunnel blockage are also presented. Attachment-line location was used as a first-order parameter for matching full-scale ice shapes, following the findings of previous investigations on hybrid airfoils. Methods for controlling the spanwise variation of attachment line due to flow three-dimensionality were assessed with the use of angle of attack, gap between the model and tunnel wall, aerodynamic twist, and segmented flaps. Finally, model design tradeoffs are presented from the perspective of the hybrid-wing designer between competing performance parameters, such as level of agreement in matching full-scale attachment-line location, wind-tunnel load/speed limits, and model manufacturing/operational complexity.

This paper studied the aerodynamic effects of a single scalloped ice accretion and two lower fidelity ice-shape simulations. These data were compared to the aerodynamics of a clean 8.9% scale CRM65 semispan wing model at a Reynolds number of 1.6 x 10(exp 6). The clean wing experienced an aggressive, tip-first stall and showed a small, strong leading-edge vortex at lower angle-of-attack while the iced cases showed larger, seemingly weaker leading-edge vortices at similar angles. The size of these vortices is larger for the low-fidelity ice shape. The stall pattern for the iced cases was also tip-first, but more gradual than the clean wing. The high-fidelity ice shape produced streamwise flow features over the upper surface of the wing due to flow moving through gaps that exist in the ice shape geometry that disrupted the formation of the leading-edge vortices, changing the aerodynamics of the wing. These gaps do not exist in the low-fidelity shape. The low-fidelity scallop ice shape was non-conservative in its aerodynamic penalties compared to the full high-fidelity case.

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 swept-wing project. These models were tested in the Walter H. Beech wind tunnel at Wichita State University and at the ONERA (Office national d'etudes et de recherches aerospatiales) F1 facility, respectively. The data collected in the Wichita State 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 by 10 (sup 6). 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 attached to this smooth ice shape as another fidelity variant. The data indicates that the geometric fidelity of the ice shapes resulted in significant differences in lift and drag. These results were similar at both facilities over the wide range of test conditions utilized.

This paper describes a wake survey system used to improve the understanding of the underlying flowfield and aerodynamics of a swept wing with ice accretions. This system allows the rapid collection and analysis of large amounts of flowfield data by utilizing an array of five-hole probes on a precisely controlled traverse arm. Flowfield structure on the surface of the wing is acquired using an oil flow visualization technique and correlated to the associated wake survey. This method allows quantitative calculations such as spanwise lift and drag to be compared with qualitative measurements and observations to enhance the understanding of the aerodynamics of wings containing ice accretions. Wind tunnel tests for a range of configurations are presented and analyzed in this paper. Results based on this wake survey method are compared with traditional measurement techniques such as force balance measurements to assess their accuracy.

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.

This report presents the key results from the first two years of a program to develop experimental icing simulation capabilities for full-scale swept wings. This investigation was undertaken as a part of a larger collaborative research effort on ice accretion and aerodynamics for large-scale swept wings. Ice accretion and the resulting aerodynamic effect on large-scale swept wings presents a significant airplane design and certification challenge to air frame manufacturers, certification authorities, and research organizations alike. While the effect of ice accretion on straight wings has been studied in detail for many years, the available data on swept-wing icing are much more limited, especially for larger scales.

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.

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.

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 /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.