Computational simulation of ice accretion and shedding trajectory of a rotorcraft in forward flight with strong rotor wakes

To ensure safe flight in icing conditions it is essential to understand ice accretion, its effect on aerodynamic performance and ice shedding in any aircraft certification program. Ice fragments shed from a rotorcraft windshield and other locations can be detrimental if they are ingested into the engine intake or impinge on the tail rotor.

Because of the lack of experimental data about the forces and moments acting on ice in such a complex flow field, the computational simulation of ice shedding trajectories becomes essential. This study presents a methodology to predict the location of ice accretion and break-off, ice shape and shedding trajectory in a rotorcraft flow field with strong rotor wakes during forward flight.

The methodology includes the creation of an aerodynamic database for different ice shapes (rectangle, disc, ellipse, and glaze ice shape) at various combinations of Euler angles; the analysis of rotorcraft flow field by computational fluid dynamics for different advance ratios; and a six degree-of-freedom trajectory analysis using artificial neural networks and the Monte Carlo method.

The actuator surface method was applied to account for the rotor wake effect, which is capable of modeling the tip vortices and inboard sheets emanating from the rotor blades. The main results are a probability map of the ice shedding trajectory footprints on the engine intake and tail rotor planes.

Disc-shaped ice fragments with a sharp edge turned out to be most dangerous. The rotation of the main rotors also substantially affected ice accretion and shed trajectory, indicating the importance of integrated simulations of all components when designing ice protection systems for rotorcraft.