MEAN VELOCITY-FIELD RELATIVE TO A RUSHTON TURBINE BLADE

The 3-D flow field relative to a rotating Rushton turbine blade is acq uired for fully turbulent tank conditions by synchronizing LDA measure ments with the output of a shaft-mounted encoder. This makes it possib le to capture the impeller stream velocity field, including the detail s of the vortices behind the blades. Mean velocity data at three impel ler speeds show the extent of periodicity and the axes and structure o f the vortices. Pumping capacities are determined and it is shown that the radial jet is a consequence of fluid entrainment into the vortice s. Deformation rates based on gradients of mean velocity are calculate d. Close to the blade they can exceed impeller rotational frequency by as much as two orders of magnitude. To a first approximation, the nor malized mean flow field is independent of impeller speed.