Numerical study on stall characteristics of a triangular airfoil in low Reynolds number compressible flow

Due to the low density and low temperature of the atmosphere on the surface of Mars, Mars aircraft are usually in compressible flow at low Reynolds number. In this paper, the dynamic stall characteristics of triangular airfoil with reduced frequencies of 0.09 and 0.15 are studied based on large eddy simulation (LES). The incoming Mach number is 0.5 and the Reynolds number is 3000. The results show that, with the increase of reduced frequency, the lift and drag coefficient in dynamic motion gradually deviates from the static lift and drag coefficient, but the dynamic stall angle of attack has little difference with the static stall angle of attack. In order to obtain the main flow structure during blade dynamic stall, dynamic mode decomposition (DMD) was used to decompose and reconstruct the velocity vector field around the blade. The results show that the DMD decomposition modes mainly include time-average flow field with separation flow at the blade tail, low-frequency large-scale separation flow at the blade leading edge and tail enrolling effect, and high-frequency separation and attachment flow at the blade apex downstream. The first 20 modes reconstruction can basically restore the main flow structure of the flow field.