Design of control-assisted transonic pressure recovery profiles using vortex generators

An experimental study was conducted to assess the boundary-layer flow state associated with Stratford pressure recovery profiles in a transonic flow at Mach 0.7 and the enabling role of vortex generator devices for completing fully attached pressure recoveries across shorter chordwise distances. Airfoil geometries with Stratford-like pressure recovery distributions were designed and tested to show that both subcritical and supercritical airfoil cases retain the classical marginally separated condition across the recovery region, with the former showing a greater separation stability margin at off-design conditions. It was determined that the pressure recovery in the supercritical case was immediately preceded by a discrete pressure increase across the shock, which, when coupled to the adverse pressure gradients imposed by the Stratford pressure recovery profile, resulted in separation of the boundary layer at a higher Mach number of 0.75. The airfoils were also tested with two micro-vortex generator configurations to show a fully attached recovery process across shorter distances than the Stratford limit. The vortex generators were observed to introduce circulation-based effects into the flowfield, resulting in local supersonic regions within the vicinity of their placement.