Experimental investigations on vortex breakdown over delta wings with Doppler global velocimetry

The fluid dynamic properties of the flow over a delta wing are still not yet fully understood. Recent numerical simulations have shown that the stability of the vortices could be best judged and observed by resolving the unsteady velocity distributions of the axial velocity vector component in the vortex core region. For an experimental validation of these numerical results it is necessary to obtain the three dimensional velocity distribution in the vortex core. Obtaining the velocity distribution should work without influencing the flow because the stability property is very sensitive against any disturbance in the flow. A non intrusive optical technique is chosen as adequate to measure the velocity distribution: Doppler Global Velocimetry. It is based on the Doppler shift of laser light due to scattering at moving particles. By extensively seeding the flow with these particles it was possible to determine the unsteady three dimensional velocity distribution in the vortex core. The experiment shows a good agreement with the numerically predicted flow structures.