Design of assisted transonic pressure recovery using passive flow control for airfoil geometries

An investigation was conducted to assess the ability of a boundary layer to remain attached across a Stratford pressure recovery in a transonic flow and to verify if recovery across shorter chordwise distances was possible with the aid vortex generators (VG). Airfoil geometries with Stratford-like pressure recovery regions approaching C_f,x = 0 were designed and tested to show that both subcritical and supercritical airfoil cases remain attached across the pressure recovery region with the former showing a greater stability margin at off-design conditions. It was determined that the pressure recovery in the supercritical case was led by the 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. The airfoils were also tested with two micro-VG configurations to show a fully-attached recovery process across shorter distances than the Stratford limit, with the further upstream placement of 25H showing better performance. The VGs were observed to introduce circulation-based effects into the flow field resulting in local supersonic regions across their chordwise location, which in some cases introduced a secondary shock upstream of the VG location.