Large-eddy simulation on laminar-separation-bubble affected by swirling flow simulating propeller slipstream for low Reynolds number airfoil flow

To investigate the effects of a propeller slipstream on a laminar separation bubble (LSB) over an airfoil, large-eddy simulations (LESs) were performed on the flow around the NACA0012 airfoil influenced by the wake of a propeller. The Reynolds number was 30,000, and the angle of attack was 7 degrees. The propeller-induced flow was simulated using an actuator disk model, and the characteristics of the swirling flow of propeller-induced flow was changed as the parameter to clarify the effects of the swirling flow of propeller slipstream on LSB characteristics. On the upwash side, as the swirl number increases, the separation point of LSB moves toward the leading edge. This is due to an increase in effective angle of attack. When the swirl number is high, there is no turbulent reattachment, and the flow bursts. On the downwash side, due to a decrease in effective angle of attack, the separation point of LSB moves linearly toward the trailing edge as the swirl number increases, and the reattachment point also moves linearly toward the trailing edge. The LSB region becomes smaller as the swirl number increases. Regarding the local lift coefficient, both the upwash and downwash sides show smaller lift coefficients as the swirl number increases. This is because the flow bursting occurs on the upwash side, while the effective angle of attack decreases on the downwash side. Additionally, in the absence of swirling flow, both the upwash and downwash sides show an increase in lift coefficient by the local increases of the uniform flow.