Investigating a stretched vortex with ultrafast two-dimensional ultrasonic speckle velocimetry

Ultrasonic speckle velocimetry (USV) was recently introduced as a new ultrafast tool for measuring fluid velocities in two dimensions by analyzing the speckle signal backscattered from particles moving with the flow [Sandrin , Appl. Phys. Lett. 78, 1155 (2001)]. An experimental study of a stationary stretched vortex is presented, which demonstrates the efficiency of ultrafast 2D USV in terms of quantitative assessment of vortical flows. The full velocity field is recovered and compared to the Burgers model for two different fluids: water and milk. The dependence of the vortex characteristics on the main control parameter is investigated. (C) 2001 American Institute of Physics.