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.