Sam Lee

Experimental Investigation of Simulated Large-Droplet Ice Shapes on Airfoil Aerodynamics

An experimental investigation was conducted to study the aerodynamic effect of simulated supercooled largedroplet ice accretion on a modie ed NACA 23012 airfoil. Forward-facing quarter-round simulations with heightto-chord ratios of 0.0083 and 0.0139 were used at a Reynolds number of 1 :8 £ 10 6 . When the simulated ice was placed at critical chordwise locations, a long separation bubbleformed downstream of thesimulated ice shape and effectively eliminated the formation of a large leading-edge suction peak that was observed on the clean NACA 23012 airfoil. This resulted in a dramatic reduction in the maximum lift coefe cient, as low as 0.27, when the larger simulated ice shape was located at 12% chord. Because the airfoil loading distribution was severely altered, large changes in airfoil pitching moments and e ap-hinge moments were also observed.

Effect of High-Fidelity Ice-Accretion Simulations on Full-Scale Airfoil Performance

The simulation of ice accretion on a wing or other surface is often required for aerodynamic evaluation, particularly at small scale or low Reynolds number. Although there are commonly accepted practices for ice simulation, there are no established and validated guidelines. The purpose of this paper is to report the results of an experimental study establishing a high-fidelity, full-scale, iced-airfoil aerodynamic performance database. This research was conducted as a part of a larger program with the goal of developing subscale aerodynamic simulation methods for iced airfoils. Airfoil performance testing was carried out at the ONERA F1 pressurized wind tunnel using a 72 in. (1828.8 mm) chord NACA 23012 airfoil over a Reynolds number range of 4.5 x 10 6 to 16.0 × 10 6 and a Mach number range of 0.10 to 0.28. The high-fidelity ice-casting simulations had a significant impact on the aerodynamic performance. A spanwise-ridge ice shape resulted in a maximum lift coefficient of 0.56 compared with the clean value of 1.85 at Re = 15.9 x 10 6 and M = 0.20. Two roughness and streamwise shapes yielded maximum lift values in the range of 1.09 to 1.28, which was a relatively small variation compared with the differences in the ice geometry. The stalling characteristics of the two roughness ice simulations and one streamwise ice simulation maintained the abrupt leading-edge stall type of the clean NACA 23012 airfoil, despite the significant decrease in maximum lift. Changes in Reynolds and Mach numbers over the large range tested had little effect on the iced-airfoil performance.

A Wind Tunnel Study of Icing Effects on a Business Jet Airfoil

Aerodynamic wind tunnel tests were conducted to study the effects of various ice accretions on the aerodynamic performance of a 36-inch chord, two-dimensional business jet airfoil. Eight different ice shape configurations were tested. Four were castings made from molds of ice shapes accreted in an icing wind tunnel. Two were made using computationally smoothed tracings of two of the ice shapes accreted in the icing tunnel. These smoothed profiles were then extended in the spanwise direction to form a twodimensional ice shape. The final two configurations were formed by applying grit to the smoothed ice shapes. The ice shapes resulted in as much as 48% reduction in maximum lift coefficient from that of the clean airfoil. Large increases in drag and changes in pitching moment were also observed. The castings and their corresponding smoothed counterparts yielded similar results. Little change in performance was observed with the addition of grit to the smoothed ice shapes. Changes in the Reynolds number (from 3×10 to 10.5×10) and Mach number (from 0.12 to 0.28) did not significantly affect the iced-airfoil performance coefficients.

Investigation of Factors Affecting Iced-Airfoil Aerodynamics

A summary of the effects the ice-accretion geometry, size, and location; the airfoil geometry; and the e ight Reynolds number on iced-airfoil aerodynamics, based on the e ndings of the recent University of Illinois investigations,ispresented.Fourairfoilsweretestedwithsimulatedglaze-icehornandspanwiseridgeice.Increasing theiceshapeheightgenerally resultedin moresevereperformancedegradation.Theexceptionwaswhentheiceshapewas locatedattheleadingedgeoftheairfoil,whereincreasedice-shapeheightdidnotsignie cantlydegradeperformance. Varying the leading-edge radius of glaze-icehorn did not have a large effect on airfoil performance. The variations in the geometry of the simulated ridge ice had some effect on airfoil aerodynamics, with (of the shapes tested ) the half-round shape having a signie cantly higher maximum lift. Iced-airfoil aerodynamics were relatively insensitive to Reynolds number variations. Large differences in iced-airfoil aerodynamics were observed between different airfoil geometries. The e ndings showed that an airfoil’ s sensitivity to ridge-ice accretions (which usually forms between 10 and 20% chord )was largely dependent on its load distribution. The airfoil that was very front-loaded, with large leading-edge suction, had the most severe performance degradation due to this type of ice accretion.

Effects of simulated-spanwise-ice shapes on airfoils - Experimental investigation

An experimental investigation was conducted to determine the effect of simulated-spanwise-ice shapes on airfoil aerodynamics. The simulated ice shapes were tested on the NACA 23012 and the NLF 0414 airfoils at Re = 1.8 million. The ice shapes produced very different results on the two airfoils. The effects of the simulated ice shapes were much more severe on the NACA 23012, with a Cf,mx as low as 0.25 for the ice shape with a height to chord ratio of 0.0139. The lowest C,,,, measured for the NLF 0414 with same ice shape was 0.68. The effect of the simulated ice shape on the flap hinge moment was much more severe on the NACA 23012 than. on the NLF 0414. The NACA 23012 effects were more severe due to the large adverse pressure gradients at the ice-shape location. Various simulated ice shape size and geometries were investigated on the NACA 23012. The aerodynamic penalties (in C, Cd, C,, and C,) became more severe as the height to chord ratio of the simulated ice shape was increased from 0.0056 to 0.0139. The variations in the simulated ice shape geometry also had measurable effects on the airfoil aerodynamics.

Implementation and Validation of 3-D Ice Accretion Measurement Methodology

A research program has been implemented to develop and validate the use of a commercial 3-D laser scanning system to record ice accretion geometry in the NASA Icing Research Tunnel. A main component of the program was the geometric assessment of the 3- D laser scanning system on a 2-D (straight wing) and a 3-D (swept wing) airfoil geometries. This exercise consisted of comparison of scanned ice accretion to castings of the same ice accretion. The scan data were also used to create rapid prototype artificial ice shapes that were scanned and compared to the original ice accretion. The results from geometric comparisons on the straight wing showed that the ice shape models generated through the scan/rapid prototype process compared reasonably well with the cast shapes. Similar results were obtained with the geometric comparisons on the swept wing. It was difficult to precisely compare the scans of the cast shapes to the original ice accretion scans because the cast shapes appear to have shrunk during the mold/casting process by as much as 0.10-inch. However the comparison of the local ice-shape features were possible and produced better results. The rapid prototype manufacturing process was shown to reproduce the original ice accretion scan normally within 0.01-inch.

Development of 3D Ice Accretion Measurement Method

A research plan is currently being implemented by NASA to develop and validate the use of a commercial laser scanner to record and archive fully three-dimensional ice shapes from an icing wind tunnel. The plan focused specifically upon measuring ice accreted in the NASA Icing Research Tunnel (IRT). The plan was divided into two phases. The first phase was the identification and selection of the laser scanning system and the post-processing software to purchase and develop further. The second phase was the implementation and validation of the selected system through a series of icing and aerodynamic tests. Phase I of the research plan has been completed. It consisted of evaluating several scanning hardware and software systems against an established selection criteria through demonstrations in the IRT. The results of Phase I showed that all of the scanning systems that were evaluated were equally capable of scanning ice shapes. The factors that differentiated the scanners were ease of use and the ability to operate in a wide range of IRT environmental conditions.

Validation of 3-D Ice Accretion Measurement Methodology for Experimental Aerodynamic Simulation

Determining the adverse aerodynamic effects due to ice accretion often relies on dry-air wind-tunnel testing of artificial, or simulated, ice shapes. Recent developments in ice-accretion documentation methods have yielded a laser-scanning capability that can measure highly three-dimensional (3-D) features of ice accreted in icing wind tunnels. The objective of this paper was to evaluate the aerodynamic accuracy of ice-accretion simulations generated from laser-scan data. Ice-accretion tests were conducted in the NASA Icing Research Tunnel using an 18-in. chord, two-dimensional (2-D) straight wing with NACA 23012 airfoil section. For six ice-accretion cases, a 3-D laser scan was performed to document the ice geometry prior to the molding process. Aerodynamic performance testing was conducted at the University of Illinois low-speed wind tunnel at a Reynolds number of 1.8 10(exp 6) and a Mach number of 0.18 with an 18-in. chord NACA 23012 airfoil model that was designed to accommodate the artificial ice shapes. The ice-accretion molds were used to fabricate one set of artificial ice shapes from polyurethane castings. The laser-scan data were used to fabricate another set of artificial ice shapes using rapid prototype manufacturing such as stereolithography. The iced-airfoil results with both sets of artificial ice shapes were compared to evaluate the aerodynamic simulation accuracy of the laser-scan data. For five of the six ice-accretion cases, there was excellent agreement in the iced-airfoil aerodynamic performance between the casting and laser-scan based simulations. For example, typical differences in iced-airfoil maximum lift coefficient were less than 3 percent with corresponding differences in stall angle of approximately 1 deg or less. The aerodynamic simulation accuracy reported in this paper has demonstrated the combined accuracy of the laser-scan and rapid-prototype manufacturing approach to simulating ice accretion for a NACA 23012 airfoil. For several of the ice-accretion cases tested, the aerodynamics is known to depend upon the small, three-dimensional features of the ice. These data show that the laser-scan and rapid-prototype manufacturing approach is capable of replicating these ice features within the reported accuracies of the laser-scan measurement and rapid-prototyping method; thus providing a new capability for high-fidelity ice-accretion documentation and artificial ice-shape fabrication for icing research.

An experimental and computational investigation of spanwise-step-ice shapes on airfoil aerodynamics

The objective of this research was to study the effects of spanwise-step-ice accretions (resulting from large droplet icing conditions) on subsonic aircraft aerodynamics. The airfoil investigated was a modified NACA 23012 with a simple flap. An experimental and computational program was conducted using simulated ice accretions to determine the sensitivity of ice shape size and location on airfoil performance and control as a function of angle of attack and flap deflection. Focus is paid on the critical conditions where the aerodynamic performance, and the hinge moment in particular, changes rapidly and non-linearly. The experimental program included wake surveys, surface pressure taps, and force-balance measurements to obtain lift, drag, pitching moment, and hinge-moment coefficients for a large variety of geometry and flow conditions. The accompanying computational investigation was performed with a high-resolution full Navier-Stokes solution using a solution-adaptive unstructured grid for both non-iced and iced configurations. Results are presented for experiments and predictions of sectional aerodynamic characteristics where the quarter-round ice shape heights of 0.0083 and 0.0139 chords resulted in a dramatic decrease in maximum lift coefficients as well as significant reductions in hinge moments for positive angles of attack.

Characteristics of Runback Ice Accretions on Airfoils and their Aerodynamics Effects

The initial results of a research program to investigate runback ice accretions due to hotair ice protection systems, scaling of external flow parameters for testing thermal systems and the resulting aerodynamic effects are presented. The scaling of external flow parameters for testing thermal anti-icing systems in icing tunnel investigations was developed and tested. An icing tunnel test was conducted at the NASA Glenn Icing Research Tunnel to evaluate three scaling methods developed to match thermodynamic and droplet impingement parameters. A typical business jet wing section with a hot-air anti-icing system was used for the test. Data collected from the test included surface temperatures (using both thermocouples and an IR camera), photographs, high definition video, tracings and molds. Results of the scaling analysis showed that a useful and qualitatively accurate scaling method was developed for scaling thermal anti-icing systems for ground testing. However, further development and investigation of the method and governing equations is required, including generating full-scale runback ice accretions for quantitative evaluation of the scaling methods. A wind tunnel test was also conducted to evaluate the aerodynamic performance effects of simulated ice shapes based on the shapes observed in the icing tunnel test. Aerodynamic testing revealed significant aerodynamic penalties for all flight conditions tested.