Reynolds number scaling of flow in a stirred tank with Rushton turbine. Part II — Eigen decomposition of fluctuation

Abstract

We consider the question of scaling of flow within a stirred tank with increasing Reynolds number. Experimental results obtained from two different tanks of diameter 15.25 and 29.21 cm with a Rushton turbine operating at a wide range of rotational speed is considered for the scaling analysis. The resulting Reynolds number of the flow ranges from 4000 to about 80,000. Phase locked stereoscopic PIV measurements have been performed in order to obtain all three components of velocity on three different vertical planes close to the impeller. The scaling of plane-averaged mean flow was explored in the companion part-I of the paper. The scaling of rms and skewness of fluctuation about the mean is investigated here. The fluctuation about the mean is explained in terms of time-dependent oscillation of the impeller-induced jet and tip vortex components of the flow. The spatial structure of the instantaneous fluctuation about the mean is investigated in terms of eigenmodes obtained using proper orthogonal decomposition with the method of snapshots. The scaling of energy content of the dominant eigenmodes with Re is investigated.