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

Abstract

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 iceaccretion documentation methods have yielded a laser-scanning capability that can measure highly three-dimensional 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-inch chord, 2-D straight wing with NACA 23012 airfoil section. For six iceaccretion 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 6 and a Mach number of 0.18 with an 18-inch 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 four 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% with corresponding differences in stall angle of approximately one degree 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, threedimensional 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.casting = drag coefficient for the three-dimensional casting C d,rpm = drag coefficient for the RPM simulation ΔC d,rms = root-mean-square percent difference in drag coefficient between the RPM simulation and the threedimensional casting simulation over a given angle of attack range C l = lift coefficient C l,max = maximum lift coefficient, coincident with stalling angle C m = quarter-chord pitching moment C p = pressure coefficient k = ice roughness height or ice thickness LWC = Liquid Water Content M = freestream Mach number N = number of angles of attack Re = freestream Reynolds number based on chord α = angle of atta...

Implementation and Validation of 3-D Ice Accretion Measurement Methodology

“…Although the PolyJet method was capable of manufacturing layers of this height, its tolerance was greater than the roughness height. This was verified by the aerodynamic results shown in Broeren et al 12 that showed that the maximum lift coefficients of the SLA and PolyJet ice shapes were 6% and 11% higher than the cast shape. Figure 26 shows the comparison plots for the rime ice accretion from run ED1977.…”

“…Artificial ice shapes were also constructed using the traditional mold/casting methods for both geometric and aerodynamic comparisons. The results of the aerodynamic comparison between the RPM shapes and the cast shapes are included in a companion paper by Broeren et al 12 This paper presents the results and analysis of the geometric comparison between the RPM shapes and the cast shapes.…”

“…The results and analysis of the geometric comparison between the RPM shapes and the cast shapes are included in this paper. The results of the aerodynamic comparison between the RPM shapes and the cast shapes are included in the companion paper by Broeren et al 12 The methods used for processing raw ice accretion scan data into a water-tight 3-D mesh for documentation and rapid prototype manufacturing for aerodynamic testing are described in this section. These methods were used to process data acquired with a Romer Absolute scanner using Geomagic software.…”

Validation of 3-D Ice Accretion Measurement Methodology Using Pressure-Sensitive Paint

“…The digital scans were processed and used to make RPM ice shapes to compare to the castings. A total of six ice shapes were replicated and are discussed by Broeren et al, 5 although only two of these were tested with PSP. This further testing with PSP was used to help resolve observed aerodynamic differences between the castings and RPM shapes for a horn shape ( Fig.…”

“…The aerodynamic performance validation results are presented and analyzed by Broeren et al, 5 who concluded that the 3-D laser scanner method was valid for most of the ice shape classifications tested. However, they found that the aerodynamics for a horn shape and a fine roughness shape generated from the new method did not satisfactorily agree with the respective casting aerodynamics.…”