UAV Icing: Numerical Simulation of Icing Effects on Wing and Empennage

Abstract

In-flight icing can result in severe aerodynamic performance penalties for unmanned aerial vehicles. It is therefore important to understand to which extent ice will build up on fixed-wing unmanned aerial vehicles wings and empennages, namely rudder and elevator, and how this ice will impact the aerodynamic performance and limits the flight envelope. This work investigates numerically icing effects on wing and empennage over a wide range of icing parameters. This is conducted using the icing CFD code FENSAP-ICE on the Maritime Robotics PX-31 Falk UAV. Therefore, the 2D profiles of these airfoils, which are RG-15 for the wing and SD8020 for rudder and elevator, are investigated. The investigated angles of attack are between –5° and 14° in 0.5° increments. Furthermore, the icing conditions are chosen according to the FAA CS 25 Appendix C for continuous maximum and intermittent maximum icing. A broad range of temperatures, droplet median volumetric diameters, and the corresponding liquid water contents are simulated to generate a understanding of the icing effects according to Appendix C. An automation script to enable a more effective parallel execution of the in total 142 simulations of each airfoil has been used. The results of the simulations are used to calculate the change in the lift coefficient cl, the drag coefficient cd and the momentum coefficient cm, and an estimate of the total accreted ice mass. The aerodynamic performance penalties are strongly dependant on the environmental conditions. For both icing envelopes, two different worst case conditions are identified. For continuous maximum this condition lies at –2 °C and a droplet size of 15 μm, for intermittent maximum at –6 °C and 20 μm. For continuous maximum conditions the maximum lift can decrease by 37%, and the drag increase by 107%. For intermittent maximum the maximum lift can decrease by 35%, and the drag increase by 103%.