Effects of pulsed and continuous jet vortex generators in a turbulent boundary layer flow - an investigation by using two high-speed stereo PIV systems

Continuous and pulsed jet vortex generators are well known for their capability of inhibiting flow separation due to enhanced mixing in turbulent boundary layer (TBL) flows. Jet vortex generators of adequate geometries produce streamwise vorticity which in interaction with the TBL flow increase the wall normal fluid transport. For a given ideal configuration this transport depends on the ratio between jet and the bulk velocity, but with a moderate jet velocity - even in a pulsed mode- the wall normal fluid exchange can be organized more efficient. Especially the shifts of high momentum fluid towards the wall produce regions of higher wall-shear stress in comparison with the situation without jet interaction. This is a favourable condition for TBL flows with adverse pressure gradients e.g. at flaps of high-lift-configurations to remain attached to the wall. The efficiency of such stream-wise vorticity induced wall-shear stress has been found to be increased for small (average) distances of the vortex core to the wall. Elaborated DNS of a strong jet vortex generator in a turbulent boundary layer flow at a moderate Reynolds number show the complex interaction between the stream-wise vorticity producing jet flow wake and the new formation of turbulent structures in the further development of the TBL.