Transition from turbulent to transitional flow in the top half of a stirred tank

The limits of fully developed turbulence are defined in the wall jet and in the recirculation flow for three different impeller geometries: A310, HE3 and PBTD. At two different tank scales, mean velocity profiles in both the wall jet and the recirculation flow were measured to determine whether the condition of fully turbulent self-similarity is satisfied. Higher impeller Reynolds numbers are able to keep the flow fully turbulent higher in the tank. In addition to the expected effect of impeller Reynolds number, the fluid also affected the flow regime. Measurements in a pilot scale stirred tank gave similar results. Although the power number is often constant for Re > 20 000, an impeller Re >= 300 000 is required to keep the flow in the fully turbulent regime in the top third of the tank and in the recirculation zone. (C) 2013 Elsevier Ltd. All rights reserved.