PIV study of the Influence of Large Scale Streamwise Vortices on a Turbulent Boundary Layer

Vortex generator jets have been used to generate large scale longitudinal vortices embedded in a flat plate turbulent boundary layer. The investigation has been performed in a water tunnel, measuring instantaneous flow fields in planes parallel and normal to the flat plate, using particle image velocimetry. The objective of the research was to observe the response of near wall turbulence to the imposed perturbing flow. It is shown that a small amplitude forcing vortical flow produces significant influence on the mean and fluctuating velocity profiles. Moreover, particle image velocimetry permitted to speculate upon the behaviour of the wall velocity streaks under the action of the perturbing forcing vortical flow.