On the Direct Measurement of Turbulence Energy Dissipation in Stirred Vessels with PIV

The mean flow and turbulence fields and the turbulence energy dissipation rate (ε) in a vessel stirred by a hydrofoil impeller were studied using particle image velocimetry (PIV). The vessel diameter was 100 mm, and it was stirred by an impeller of diameter D = T /3. The impeller Reynolds number was 40 000 to ensure fully turbulent flow in the vessel. Particular attention was paid to the effect of spatial resolution on the estimation of ε, which was determined directly from its definition, i.e., by measuring the instantaneous spatial gradients of the Reynolds stresses. The data provide new information on the quantification and distribution of ε in stirred vessels and indicate that estimates of dissipation based on a constant length scale across the vessel and the distribution of the turbulence levels may underestimate the maximum and overestimate the minimum levels of ε present in a stirred vessel.