Discrete vortices on delta wings with unsteady leading-edge blowing

An experimental investigation on how does leading-edge blowing with constant and spatially varying frequencies affect the flow field above a delta wing was done. A new way of investigating such and other leading-edge vortex flows is presented. The method looks at instantaneous frames of particle image velocimetry (PIV) measurements and detects the discrete vortices within them using the a2-criterion. The method was seen to be sensitive to the spatial resolution of the measurements, but more details of the flow were acquired than by using the time-averaged data only. Actuation was seen to majorly transform the flow at post-stall angles of attack. The number of detected vortices more than doubled, increasing the total circulation as well. Spatially varying frequency actuation was seen to distribute the strongest vortices in an annular region, whereas the constant frequency actuation had most of them concentrated closer to the wing surface. At stall angles of attack the effect was less. However, the concentration of the discrete vortices with highest circulation was seen to change its position for both actuations. The total number of vortices slightly decreased, but their circulation increased.