High-lift enhancement using active flow control

The high-lift performance of an airfoil with a single-element flap is enhanced using fluidic actuation based on synthetic jet technology. Acutation is implemented using a spanwise array of individually controlled discrete synthetic jets with variable spanwise spacing that issue in a direction nominally-tangential to the flap immediately upstream of separation. The jets are used to engender and manipulate concentrations of vorticity in a manner that leads to improved flow attachment. The resulting increase in suction upstream and downstream of the jet array leads to a substantial increase in lift (at δ;= 25°, Re_c = 3.3·10⁵ and α = 4°ΔC_L of up to 0.82 relative to the unactuated flow can be realized). The effect of the spanwise actuation wavelength λ is investigated with the objective of optimizing the actuation momentum coefficient Cμ. It is shown that for a given ΔC_L, Cμ has a minimum for some spanwise actuation wavelength. Measurements of the three-dimensional flow field in the vicinity of an actuator jet show that flow attachment is accompanied by the formation of a counter-rotating streamwise vortex pair, and favorable streamwise pressure gradient downstream of the actuator.