Angle-resolved stereo-PIV measurements close to a down-pumping pitched-blade turbine

The present work employs a stereoscopic-PIV technique to obtain angle-resolved fields of all three velocity components close to a T/3T/3, 45∘45∘ down-pumping pitched-blade turbine operated at 300 rpm in a 0.29 m diameter vessel. The measurements were made at blade angles 7.5∘7.5∘ apart, with 300 measurements taken at each blade position, in order to calculate angle-resolved mean velocity fields and turbulence quantities. Turbulent kinetic energy (kk) distributions were obtained using (i) a pseudo-isotropic approximation, from two velocity components and (ii) a full calculation from all three velocity components. The two calculation methods for kk yielded similar results, indicating that data from 2-D PIV measurements yield reasonable estimates of the turbulence kinetic energy. The tangential velocity components at the impeller discharge from PIV were in good agreement with data from LDA analysis. A kinetic energy balance across the impeller was performed (i) rigorously and (ii) using approximations which neglected second- and higher-order velocity cross-correlations. Both analyses show that around 44% of the total power consumed by the impeller is dissipated in the impeller region. The average rate of dissipation of kinetic energy is about 40 times higher in the impeller region than the volume-average dissipation rate in the whole vessel.