2-D LDA-measurements in a wake

Flow field measurements in the wake of a flat plate at Reynolds numbers of 20,000 to 60,000, based on the trailing edge thickness d, have been performed. In order to obtain the time-dependent velocity change of the shed eddies, a conditional sampling technique was developed to establish a known phase reference for an ensemble-averaged representation of the instantaneous velocity change during the passage of a vortex pair. Evaluation of velocity data showed that a representation of the steady and periodic velocity components and turbulent velocity can be used to obtain Reynolds shear stress and vorticity. Comparison of the phase relationships in the downstream direction allowed the estimation of the convection speed of the eddies and their development downstream.