Stereoscopic particle image velocimetry measurements of the flow around a Rushton turbine

The principles of stereoscopic particle image velocimetry (PIV), including distortion compensation, were applied to the turbulent flow in a vessel sti rred by a Rushton turbine. An angular offset configuration was used and til t-axis lens mounts were incorporated in order to satisfy the Scheimpflug co ndition, significantly reducing the ordinarily large depth of field require ments of such configurations. A distortion compensation procedure, or in si tu calibration, was utilized in place of the ray tracing, or mechanical reg istration, used in previous studies. The calibration procedure was validate d using two tests, one a rigid translation of a speckle target, the other t he viscous flow between two concentric cylinders. The results of the tests suggest the success with which the distortion compensation procedure may be applied to real fluid flows. Phase-locked instantaneous data were ensemble averaged and interpolated in order to obtain mean 3-D velocity fields on a cylindrical shell enclosing the turbine blade. From these fields, the tip vortex pairs and the radial jet documented in previous studies of mixer flo ws were easily identified.