A device for introducing helical perturbations into a trailing line vortex

A perturbation generator has been designed which can be attached to the centerbody of a matched airfoil type vortex generator. The device was desired to enable the introduction of helical-wave, velocity perturbations into a vortex core to permit experimental verification of theoretical vortex stability predictions. Evaluation of the perturbation generator performance, prior to vortex stability studies, has been reported here. Controlled perturbations with frequencies above 200 hz have been produced, but visual observations were insufficient to confirm their helical character. Hot wire velocity spectrum data have confirmed the device's ability to introduce controlled frequency fluctuations. In addition, other flow oscillations have been discussed which can influence the controllability of vortex perturbations.