Investigation of the parallel blade-vortex interaction at low speed

Abstract

Low-speed wind-tunnel tests were conducted to investigate the parallel blade-vortex interaction. Flowvisualization 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 pressuretapped 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 c vg = chord length of vortex generator wing Q = section lift coefficient of instrumented wing C p = pressure coefficient of instrumented wing, (P-P*)/q k = reduced frequency, ctc vg / VP -local static pressure P ini = initial local static pressurê max = maximum local static pressurê min = minimum local static pressure Pa, = freestream static pressure q = freestream dynamic pressure Re = Reynolds number T = time elapsed after vortex generation V w = freestream velocity x = longitudinal distance from instrumented wing leading edge to pressure tap x v = longitudinal distance from instrumented wing leading edge to vortex center y v = vortex generator height above wing a. = pitch angle of vortex generator «max = maximum pitch angle of vortex generator a = pitch rate of vortex generator fi m = freestream viscosity F = vortex strength Po, = freestream density

Numerical study of helicopter blade–vortex mechanism of interaction using large-eddy simulation

“…One of the challenges associated with the generation of the upstream vortex is that the wind tunnel has to be large enough, about 6 m high and 4 m wide, such that there is no wall effect. The wall effect causes a fast dissipation of the vortex before interacting with the second airfoil, Seath et al [1]. Usually the pitching or plunging airfoil generates large flow disturbances propagating towards the walls.…”

“…Previous experimental studies have shown that it is very difficult to identify the acoustic noise associated with BVI from the one caused by the wind tunnel structural noise, Seath et al [1], Abello and George [3,4].…”

“…Strong interactions which result in strong chordwise temporal pressure variations are caused by a vortex whose axis is parallel (or nearly parallel) to the spanwise axis of the blade. Seath et al [1] have shown that the parallel interactions are the most significant when compared with either oblique or perpendicular interactions.…”

Experimental Investigation of a Parallel Vortex–plate Interaction

“…This may be due to the fact that the incident vortex is diffused and diminishes in strength when it passes over a distance downstream of the leading edge. In order to reveal the details pertinent to the evolution of the surface pressure with respect to the incident vortex, the time axis of the measured pressure data is rescaled to the streamwise vortex location, with an assumption that the minimum value of the time history of pressure at the leading edge (X/C"0)04) occurs when the vortex center passes over it (Panaras 1987;Caradonna et al 1988;Seath et al 1989). The pressure port at X/C"0)04 was chosen because it had the most significant pressure pulse.…”

“…Seath et al (1989) and Straus et al (1990) investigated the blade-vortex interaction by the use of an impulsively pitching wing which created a starting vortex to interact with a downstream stationary airfoil. Their pressure measurements indicated a distinct variation of the surface pressure near the leading edge during the passage of the vortex.…”