NASA Icing Research Tunnel Research Articles

Experimental Aerodynamic Simulation of a Scallop Ice Accretion on a Swept Wing

<div class="section abstract"><div class="htmlview paragraph">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 <i>Re</i> = 11.9×10<sup>6</sup>. 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.</div></div>

Airfoil-Performance-Degradation Prediction Based on Nondimensional Icing Parameters

A physics-based empirical correlation between icing conditions and the corresponding drag coefficient was developed for NACA 0012 airfoils, and compared to other three existing prediction methods. The correlation was developed based on experimental aerodynamic databases of iced airfoils, and derived using statistical methods. The correlation model also provides drag coefficients for varying angles of attack for a given icing condition. The calculated drag coefficients resulted in 33.40% mean absolute deviation with respect to reference data from three different experimental databases. To validate the proposed degradation model and to further extend the database for helicopter-rotor performance degradation, rotating ice-accretion experiments were conducted. Four ice shapes obtained at the NASA Icing Research Tunnel were reproduced on a 53.34-cm-chord, 1.37-m-radius NACA 0012 rotor blade at the Adverse Environment Rotor Test Stand facility. Ice-shape molding and casting techniques were introduced to capture delicate ice features, such as ice feathers. The iced-airfoil castings were tested in a dry-air wind tunnel. The drag-coefficient comparison between the proposed analytical determination method and the experimental results from both rotor ice testing and icing-wind-tunnel testing showed to be satisfactory, ranging from 5 to 25% depending on the icing condition. The effect of ice feathers on drag degradation was investigated. Ice-feather formation can account for up to 25% of the drag introduced by ice accretion before stall.

Performance of a Counterflow Virtual Impactor in the NASA Icing Research Tunnel

Abstract A counterflow virtual impactor (CVI) designed for aircraft use was evaluated at the NASA Icing Research Tunnel in Cleveland, Ohio. Tests were conducted for tunnel speeds of 67 and 100 m s−1, for liquid water contents of 0.23–1.4 g m−3, and for a wide range of droplet median volume diameters (MVDs). For droplet distributions with MVDs between about 30 and 240 μm, liquid water content (LWC) measured by the CVI agreed with reference values within the uncertainty of the measurements. For a range of LWCs at 30-μm MVD, the relationship was near 1:1, and no systematic dependence of CVI results on LWC or airspeed was observed. For smaller MVDs, the CVI underestimated LWC. Decreased collection efficiency for small droplets can partially explain this effect, but the difference from reference values was larger than expected based on previous calibrations and comparisons with in situ data. Tunnel runs conducted with a flow-straightening shroud around the CVI inlet produced approximately 20% enhancements in L...

Wind Tunnel Measurements of the Response of Hot-Wire Liquid Water Content Instruments to Large Droplets

Abstract Wet wind tunnel tests were performed on more than 23 cloud liquid water content (LWC) probes and drop spectrometers at the NASA Icing Research Tunnel, with a main objective to characterize their response to large-droplet conditions. As a part of this study, the LWC and median volume diameter (MVD) reference values of the tunnel were examined, and accuracies were estimated and reported herein. Alternative MVDs were calculated from measurements conducted during the study. MVD accuracy was particularly difficult to estimate due to the lack of accepted standards, and MVD estimates were quite sensitive to the complement of instruments used to generate composite droplet spectra. Four hot-wire LWC probes were tested to characterize the LWC response as a function of cloud MVD. A response reduction was observed with increasing MVD for all three probes with cylindrical hot wires, most significant for the probe with the smallest wire diameter. The response of the Nevzorov total water content (TWC) probe, wi...

Icing-Tunnel Tests of a Glycol-Exuding, Porous Leading-Edge Ice Protection System

A glycol-exuding, porous leading-edge ice protection system was tested in the NASA Icing Research Tunnel at Lewis Research Center. Test results showed that the system was very effective in preventing ice accretion (antiice mode) or removing ice from an airfoil. Minimum glycol flow rates required for anti-icing are a function of velocity, liquid water content in the air, ambient temperature, and droplet size. Large ice caps were removed in only a few minutes using anti-ice flow rates, with the shed time being a function of the type of ice, size of the ice cap, angle of attack, and glycol flow rate. Wake survey measurements showed that no significant drag penalty was associated with the installation or operation of the system tested.