Effects of Freestream Eddies on Triangular Airfoils for Martian Rotorcraft

This study uses direct numerical simulations (DNSs) with PyFR ( www.pyfr.org ) to investigate the impact of freestream disturbances on the performance of nonconventional triangular airfoils for Martian rotorcraft. First, triangular airfoils optimized for steady uniform freestream conditions at a 12 deg angle of attack are subjected to unsteady upstream conditions containing freestream eddies with various target turbulence intensities and characteristic length scales. Results show that the freestream eddies lead to a breakdown of coherent suction-side vortices and a reduction of aerodynamic forces, with the magnitude of this effect increasing with higher turbulence intensities and larger length scales. Building on this, DNSs are then used to optimize triangular airfoils at a 12 deg angle of attack for unsteady upstream conditions containing freestream eddies. The new designs still leverage an unsteady vortex roll-up mechanism to generate lift. However, their shapes are different from those obtained when optimizing for steady uniform inflow conditions, with their apexes closer to the trailing edge. This downstream apex position allows for the smaller and weaker vortices that result from the interaction of the freestream eddies with the separated shear layer to cover a larger suction surface area. Taken together, the results demonstrate the importance of considering freestream disturbances when designing nonconventional airfoils for use on a Martian rotorcraft.