Effects of Leading-Edge Blowing Control and Reduced Frequency on Aerofoil Aerodynamic Performances

Aerofoil leading-edge fluid-blowing control is computationally studied to improve aerodynamic efficiency. The fluid injection momentum coefficient Cu (the ratio of injection to incoming square velocities times the slot's width to aerofoil's half chord-length), varies from 0.5% to 5.4%. Both static and dynamic conditions are investigated for a NACA0018 aerofoil at low speed and Reynolds number of 250k based on the aerofoil's chord-length. The aerofoil is dynamically pitched at at a reduced frequency (the pitching tangential speed to the free-stream speed ratio), varying between 0.0078 to 0.2. RANS and Unsteady RANS (URANS) are used in the simulations as based on the Transition SST and Spalart-Allmaras models, generally achieving good agreement with experimental results in lift and drag coefficients and in the pressure coefficient distributions along the aerofoil. It is found that oscillating the aerofoil can delay stall, as expected, in dynamic stall. Leading-edge blowing control can also significantly delay stall both in static and dynamic conditions as long as sufficient momentum is applied to the control. On the other hand, for a small Cu such as 0.5%, the leading-edge control worsens the performance and hastens the appearance of stall in both static and dynamic conditions. The aerofoil's oscillation reduces the differences between pitch-up and pitch-down aerodynamic performances. Detailed analysis of vorticity, pressure, velocity and streamline contours are given to provide plausible explanations and insight to the flow.