Aerodynamic Design Method of High Subsonic and Low Reynolds Number Airfoil

The propellers of both stratospheric airship and Mars UAV have special flow at high subsonic and low Reynolds number. Under this flow condition, the interference between laminar separation bubbles and shock waves makes the flow more complex, and also the design of airfoils under such flow conditions being more challenging. This paper proposes an aerodynamic design method of airfoil at high subsonic and low Reynolds number flow, combined with hybrid inverse design and design optimization. The pressure distribution integrated into the design experience will be taken as the inverse-design objective to guide the optimization process while reducing drag. An in-house Reynolds-averaged Navier-Stokes (RANS) solver-PMNS2D and the efficient surrogate-based optimizer-SurroOpt are employed to the airfoil design. Compared with the baseline airfoil E387, the transition of the direct design optimization airfoil with drag reduction is significantly delayed, which may lead to more pronounced laminar separation and unsteady flow. The transition location of the optimized airfoil is between the baseline airfoil and the direct design optimization airfoil, and a compromise can be achieved between drag reduction and unsteady effects, which verifies the effectiveness of the design method developed in this paper.