A methodology for simulating 2D shock-induced dynamic stall at flight test-based fluctuating freestream

A comprehensive methodology for simulating 2D dynamic stall at fluctuating freestream is proposed in this paper. 2D CFD simulation of a SC1095 airfoil exposed to a fluctuating freestream of Mach number 0.537 ± 0.205 and Reynolds number 6.1 × 10⁶ (based on the mean Mach number) and undergoing a 10° ± 10° pitch oscillation with a frequency of 4.25 Hz was conducted. These conditions were selected to be representative of the flow experienced by a helicopter rotor airfoil section in a real-life fast forward flight. Both constant freestream dynamic stall as well as fluctuating freestream dynamic stall simulations were conducted and compared. The methodology was carefully validated with experimental data for both transonic flow and dynamic stall under fluctuating freestream. Overall, the results suggest that the fluctuating freestream alters the dynamic stall mechanism documented for constant freestream in a major way, emphasizing that inclusion of this effect in the prediction of dynamic stall related rotor loads is imperative for rotor performance analysis and blades design.