UAV Icing: Experimental and Numerical Study of Glaze Ice Performance Penalties on an RG-15 Airfoil

A key limitation to the operational envelope of medium-sized fixed-wing unmanned aerial vehicles (UAVs) today is the risk of atmospheric in-flight icing. This type of UAV has a wingspan of up to several meters and requires an all-weather capability for long-endurance and long-range missions. In contrast to the well-established icing issue in manned aviation, UAV icing is an emerging research topic. This paper aims to contribute to the ongoing validation of established numerical tools used for manned aviation. Their new arising use case are the one order of magnitude lower Reynolds number regimes of medium-sized fixed-wing UAVs. To achieve this, an experimental study with a 3D printed glaze ice shape inside the largest wind tunnel facility of the von Karman Institute in Belgium is conducted. The glaze ice shape is obtained from previous icing wind tunnel experiments. Furthermore, a numerical CFD study of the experiments with the FENSAP flow solver module of ANSYS FENSAP-ICE is performed. A final comparison of both experimental and numerical results is conducted to evaluate the glaze ice induced aerodynamic performance penalties on a clean RG-15 airfoil. The results are indicating that the chosen one-equation Spalart-Allmaras turbulence model has limited capabilities of capturing the onset of stall behaviour and achievable maximum lift of the clean and artificially glaze iced RG-15 airfoil. Nevertheless, the Spalart-Allmaras turbulence model is in general able to predict the order of the induced drag and moment penalties.