Numerical and experimental investigation of an airfoil design for a Martian micro rotorcraft

International audienceThe present paper aims at investigating the impact of airfoil design on the propulsion system for a Martian rotary wing micro air vehicle (MAV). The main challenge for flying on Mars is the atmosphere’s density and speed of sound that are significantly lower than on Earth. It leads to compressible ultra-low Reynolds number (Rec 104) flows for a 30 centimers diameter coaxial rotorcraft. Since those flows are unknown in the biosphere, numerical tools have not been validated yet. Therefore, the test section from a known depressurized experiment is simulated in 3D for solver assessment. XFoil, program for the analysis of subsonic airfoil, is also evaluated in Martian flow conditions for evaluating its ability to be used in a optimization process. Based on XFoil’s performance evaluations, both camber line and thickness distribution are optimized in 2D incompressible and compressible flows. Optimal shape is a highly cambered airfoil shifting the boundary layer separation downstream. For optimization assessment, airfoils from each optimization step are numerically evaluated with the validated solver showing that small variations in airfoil design has little impact on 2D aerodynamic performance. Compressible optimal airfoil is also proven to be more aerodynamically effective than experimentally effective airfoils from literature. Finally, the impact of airfoil shape on 3D rotor performance is evaluated with a depressurized experimental campaign recreating Martian atmosphere in terms of kinematic viscosity. The impact of gas composition is also assessed in subsonic flows