Dynamic-stall control based on an optimal approach

The present paper investigates methods to control dynamic stall using an optimal approach. Exploiting an unsteady aerodynamic sensitivity analysis based on a direct differentiation method from a two-dimensional unsteady compressible Navier-Stokes solver including a two-equation turbulence model, dynamic-stall control is conducted by minimizing an objective function defined at an instant instead of integrating for a period of time. Unsteady sensitivity derivatives of the objective function are calculated by the sensitivity code, and then optimization is carried out using a linear line search method at every physical time step. Adopting several control parameters such as nose radius, and maximum thickness of airfoil and suction, their effects on the delay or suppression of dynamic stall are examined in detail. Numerous results and comparisons indicate that the present approach yields predictive and more efficient results compared to conventional methods, and suction near the leading edge is essentially more effective than the geometric changes of airfoil in controlling dynamic stall.