Experimental and computational aerodynamic analysis of ice fragments shed from aircraft surfaces

Abstract

Icing can pose problems due to both accretions on aircraft aerodynamic surfaces as well as through shedding of large ice particles from aircraft surfaces. The shed ice causes damage by impacting downstream aerodynamic surfaces and on ingestion by aft mounted engines. Present ice trajectory simulation tools have limited capabilities due to the lack of experimental aerodynamic force and moment data for ice fragments and the large number of variables that can affect the trajectories of ice particles in the aircraft flowfield like the particle shape, size, mass, initial velocity, particle shedding location and orientation during shedding. A comprehensive literature review of experimental studies related to "random-shape" bluff body aerodynamics was conducted to support the development of a list of ice fragments for consideration in this research effort. Recommendations were also obtained from aircraft engine manufacturers and industry partners in developing the ice fragment list. Fifteen ice shapes were identified for aerodynamic testing and they were prioritized based on input from industry. The top three were selected for the present wind tunnel study. The ice fragments selected included a rectangular slab, a semicircular shell and a hemispherical shell. The literature review of experimental studies yielded a variety of methods employed by other investigators in obtaining force and moment data for randomshape bodies. However, in most previous experimental investigations force and moment data were obtained for infinite aspect ratio (2D) fragments. The research described in this thesis was performed to establish 3D six degree of freedom experimental force and moment data in the WSU 7-ft by 10-ft wind tunnel facility. The data obtained will be used in the probabilistic trajectory simulation methods of "random-shape" ice fragments employed at WSU. Experimental results are presented for five ice fragment configurations and include lift, drag and side force coefficients. In certain cases, the pitching, yawing and rolling moment coefficients are also provided. The data was reduced from the balance body axis system to the wind axis system. Transformations were developed to obtain the force and moment data at the model resolving center from the balance virtual center. The forces and moments were resolved by the WSU external balance at the virtual center. Detailed discussions are provided on the effects on the aerodynamic force and moment data due to the test mount, test section wall, model-mount interference, aspect-ratio, ice fragment shape and the associated Reynolds number. Moreover, the flowfield about selected ice fragments was computed using simulation tools like FLUENT (a Navier-Stokes solver) and GAMBIT (meshing preprocessor) to elucidate flow behavior and sting-model interference effects. Results from the computational effort are presented and include pressure coefficient contours and velocity colored streamlines.