A LDA study of turbulent flow in a baffled vessel agitated by a pitched blade turbine

Two components of mean and fluctuating turbulent velocities were measured in water by a laser Doppler anemometer in a flat-bottomed, baffled vessel agitated by a 45° pitched blade turbine impeller of 1/3rd of the vessel diameter. Using two impeller off-bottom clearances of T/4 and T/2, these measurements were carried out at many points in the vessel. Overall flow patterns have been obtained along with quantitative information on mean flows and the distribution of velocity fluctuations. The main findings are: (1) Near the base, the impeller off-bottom clearance influences decisively the flow pattern. In the case of the mid-height impeller location, a low intensity flow reversal prevails over its entirety. (2) A two-region model is proposed for the distribution of the fluctuating and mean velocities within the agitated vessel, viz., the impeller discharge zone and the remaining bulk. (3) Except in the impeller outflow stream, the fluctuating velocity measurements indicate that the turbulence is locally isotropic and virtually homogeneous. (4) The maximum turbulence intensity produced by the pitched blade turbine impeller is similar to that reported in the literature for the disc turbine. The results are broadly in agreement with the similar study of Ranade and Joshi except that a distinct region of flow reversal is found beneath the impeller at the off-bottom clearance of T/4 and the impeller discharge and total entrained flow are about 20% less