Aerodynamic Shape Optimization for Alleviating Dynamic Stall Characteristics of Helicopter Rotor Airfoil

The unsteady characteristics should be considered when to design a helicopter rotor airfoil with high aerodynamic performance. In this paper, a new optimized rotor airfoil based on the SC1095 airfoil is designed to alleviate the dynamic stall effects in helicopter rotor. In order to satisfy multi-objective requirements, the sequential quadratic programming (SQP) method is employed to optimize the unsteady characteristics of airfoil under dynamic stall conditions. The geometry of the airfoil is parameterized by the Class-Shape-Transformation (CST) method, and the C-topology body-fitted mesh is then automatically generated around the airfoil by solving the Poisson equations. Based on the grid generation technology, the unsteady RANS equations are chosen as the governing equations for predicting airfoil flowfield, and the cell-centered scheme is employed for spatial discretization of convective fluxes and viscous fluxes, and the highly-efficient implicit scheme of LU-SGS is adopted for temporal discretization. To capture the dynamic stall phenomenon of the rotor more accurately, the Spalart-Allmaras turbulence model is employed to close the RANS equations. After several cycles of optimization, the optimized airfoil with a larger leading edge radius and larger camber is obtained. The leading edge vortex and trailing edge separation of the optimized airfoil under unsteady conditions are obviously weakened, and the dynamic stall characteristics of optimized airfoil at different Mach numbers, different reduced frequencies and different angles of attack are also obviously improved compared with the baseline SC1095 airfoil. It is demonstrated that the optimized method is effective, and the optimized airfoil is suitable as the helicopter rotor airfoil.