Interaction at Low Speed

Low-speed wind-tunnel tests were conducted to investigate the parallel blade-vortex interaction. Flow-visualization tests of vortex generation performed before the pressure tests showed that a well-defined starting vortex was generated by an impulsively pitched wing. Time history of the pressure distribution on a pressure-tapped wing model was acquired as the starting vortex passed over the wing. These pressure tests revealed that a substantial pressure change near the leading edge was induced by the encountering vortex. The effects of vortex proximity, reduced frequency, and maximum pitch angle of the vortex generator on the pressure change were also investigated. Nomenclature c = chord length of instrument wing cvg = chord length of vortex generator wingQ = section lift coefficient of instrumented wing Cp = pressure coefficient of instrumented wing, (P-P*)/q k = reduced frequency, ctcvg / V^ P- local static pressure Pini = initial local static pressure ^max = maximum local static pressure ^min = minimum local static pressure Pa, = freestream static pressure q = freestream dynamic pressure Re = Reynolds number T = time elapsed after vortex generation Vw = freestream velocity x = longitudinal distance from instrumented wing leading edge to pressure tap xv = longitudinal distance from instrumented wing leading edge to vortex center yv = vortex generator height above wing a. = pitch angle of vortex generator «max = maximum pitch angle of vortex generator a = pitch rate of vortex generator fim = freestream viscosity F = vortex strength Po, = freestream densit