Simulation and Analysis of Oscillating Airfoil Ice Shapes via a Fully Unsteady Collection Efficiency Approach

The aerodynamics associated with complex ice shapes degrades performance characteristics and handling qualities of rotorcraft. As a consequence, it generates high compensatory workloads for pilots making it difficult to fly in icing environments. Simulating rotorcraft icing is challenging as rotor blades experience flows at high Mach numbers which regularly produces difficult to predict mixed rime-glaze ice shapes. In conjunction with this, the motion of the blade during each revolution produces unsteady flow field behaviour and so unsteady ice accretion needs to be considered. A fully unsteady collection efficiency approach is hereby introduced to study the ice shapes formed on an oscillating rotor airfoil. The work focuses solely on two different test cases which produce largely different ice shapes caused entirely by different ice regimes. The ice shapes are measured and compared against icing wind tunnel experimental test data and prior calculations using a different approach for computing the ice thickness. These ice structures are then subject to analyses to assess possible performance degradation against the performance of a clean airfoil. Additionally, a computational aeroacoustic study investigates the possibility of using noise to detect different types of ice formation to help aid warning the pilot of dangerous icing conditions.