Yiqiang Han

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...

Analytical and Experimental Determination of Airfoil Performance Degradation due to Ice Accretion

A physics-based, empirical correlation between icing conditions and corresponding drag coefficient was developed for NACA 0012 airfoil and compared to other three existing prediction methods. The correlation was developed based on experimental aerodynamics database of iced airfoils and derived using statistical methods. The correlation model also provides drag coefficients for varying angles of attack under a given icing condition. The calculated drag coefficients matched (33.40% mean absolute deviation) with 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 Center were reproduced on a 21-inch chord, 4.5-feet 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. Performance degradation was compared between the four iced models and the clean airfoil. 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 prior to stall. Comparison between the proposed analytical determination method and experimental results from both rotor ice testing and icing wind tunnel testing showed to be satisfactory, ranging from 25% to 6% depending on the icing condition.

Transient Heat Transfer Measurements of Surface Roughness due to Ice Accretion

A high-resolution, non-intrusive heat transfer measurement method based on Infra-Red thermography and transient heat transfer analysis is presented. This technique was successfully applied to NACA 0012 airfoils with castings of natural accreted ice surface roughness. A total of 11 representative icing conditions were reproduced at the Adverse Environment Rotor Test Stand (AERTS) facility at the Pennsylvania State University. The ice roughness was retained using ice molding and casting techniques. Roughness on casting models was categorized into a smooth zone and a rough zone. Smooth to rough zone transition location and ice limit of each case was recorded. Arithmetic averages of roughness height (Ra) were calculated for 8 locations on the chordwise direction for each of the casting models. Heat transfer measurement was conducted in a low-speed wind tunnel using thermal transient infra-red measurement techniques as well as multiple embedded heat flux and thermocouple sensors. The measured heat transfer coefficient was non-dimensionalized using Frossling numbers to account for the Reynolds variations between the compared tests. The Frossling number and roughness data were compared to LEWICE predictions in a parametric study. The effects of temperature, velocity, droplet size, liquid water content, and icing time on the heat transfer coefficient and Frossling number were examined. An overprediction of LEWICE roughness height and corresponding heat transfer rate was quantified. A 200% to 391% over-prediction of the peak heat transfer value was identified from the comparison between LEWICE prediction and experimental measurements.

Surface Roughness and Heat Transfer Improved Predictions for Aircraft Ice-Accretion Modeling

In an effort to improve the accuracy of current aircraft ice-accretion prediction tools, experimental and analytical studies have been conducted on airfoils roughened by natural ice accretion. Surface roughness introduced by ice accretion and its effect on surface convective heat transfer have been tested and modeled, based on 10 experimental test cases. A novel scaling coefficient relating the Stanton and Reynolds numbers was introduced for heat transfer comparison and modeling in turbulent regime. By coupling the ice roughness and heat transfer models together with LEWICE ice-accretion tool, an improved ice-accretion model has been achieved. Four experimental ice shapes were obtained at the Adverse Environment Rotor Test Stand laboratory for model validation. The new surface-roughness model had very good agreement in both overall ice shape and ice thickness at the stagnation line (within 5% discrepancy for four experimental cases), whereas LEWICE prediction constantly underestimated the stagnation ice t...