Effect of Spanwise Jet Spacing on Separation Control for Swept and Unswept Airfoils

Abstract

The performance of active flow control on a NACA 64 3 -618 laminar wing at an effective streamwise Reynolds number of 64,000 with and without sweep (Λ = 30° and 0°) is evaluated at post-stall angles of attack. Actuation is implemented near the leading edge using discrete, wall-normal, steady vortex generating jets (VGJs). The effect of increasing spanwise distance between jets along the leading edge of the wing is studied. For the swept wing configuration, lift coefficient shows a strong dependence on the number of vortex generating jets distributed near the leading edge. While holding blowing ratio constant and increasing spanwise jet spacing, small performance gains are noted while significantly reducing the required mass flow across a wide range of angles of attack (22º ≤ α ≤ 35º). While holding the total mass flow rate constant and increasing the spanwise distance between jets, significant performance gains are seen. The controlled straight wing configuration demonstrated a similar trend with increased spanwise jet spacing, but only over a narrow range of angle of attack (centered at α = 18º). Above this threshold, the flow displays a tendency toward multiple stable states in a seemingly unpredictable manner. Nomenclature b = span of wing [m] BR= jet blowing ratio, BR = U jet / U edge C l = airfoil section lift coefficient,pressure [Pa] Re c = chordwise Reynolds number, Re c = U eff c / ν Re eff = effective streamwise Reynolds number, Re eff = U ∞ c eff / ν U ∞ = freestream velocity [m/s] U eff = effective freestream velocity [m/s], U ∞ cos(Λ) c = chord [m] c eff = effective chord [m], c eff = c / cos(Λ) d = jet diameter [m] N jets = number of jets x = leading edge-normal coordinate [m] y = wall-normal coordinate [m] z = spanwise coordinate [m] α = airfoil angle of attack [°] Λ = wing sweep angle [°] 2 Subscripts edge = local boundary layer edge eff = effective variable measurement jet = jet exit max = maximum value of variable ps = pressure surface of wing ss = suction surface of wing ∞ = freestream