Effect of mach number on high-subsonic and low-Reynolds-number flows around airfoils

High-subsonic and low-Reynolds-number flow is a special aerodynamic problem associated with near space propellers and Mars aircrafts. The flow around airfoils and the corresponding aerodynamic performance are different from the incompressible flow at low-Reynolds-number, due to complex shock wave-laminar separation bubble interaction. The objective of this paper is to figure out the effect of Mach number on aerodynamic performance and special flow structure of airfoil. An in-house Reynolds-averaged Navier-Stokes solver coupled with gamma - Re-theta t transition model is employed to simulate the flows around the E387 airfoil. The results show that the lift slope is larger than 2 pi in the linear region. No stall occurs even at an attack angle of 20 degrees. With increase of Mach number, lift coefficient decreases when attack angle is below 10 degrees. However, once the angle of attack exceeds 12 degrees, higher Mach number corresponds to higher lift coefficient. In addition, the strength and number of shock waves are very sensitive to Mach number. With increase of Mach number, the region of reverse flow vortex near transition location becomes smaller and finally disappears, while a new reverse flow vortex appears near the trailing edge and becomes larger.