LDA measurements within a vortex-breakdown bubble

Swirl and axial velocity distributions have been measured for an axi-symmetric vortex breakdown using a laser Doppler anemometer. The streamline pattern for the breakdown bubble, constructed by integrating the axial velocity distribution, indicated that only fluid from the center portion of the upstream vortex core entered the breakdown zone. The structure consists of two 'nested' counter rotating vortices, characterized by low velocities and the presence of two stagnation points along the centerline in the upstream portion of the breakdown zone.