Large Eddy Simulation of Flow in a Stirred Tank

Abstract

Here we report on results obtained from large eddy simulations of flow inside a stirred tank performed using a spectral multidomain technique. The computations were driven by specifying the impeller-induced flow at the blade tip radius. Stereoscopic PIV measurements along with a theoretical model are used in defining the impeller-induced flow as a superposition of circumferential, jet and tip-vortex pair components. Both time-independent (fixed inflow) and time-dependent (oscillatory inflow) impeller-induced flows were considered. In both cases, the improved impeller-induced inflow allowed for the development of tip-vortex pairs in the interior of the tank. At Rem=4000 considered here, the flow in the interior of the tank naturally evolves to a time-dependent turbulent state. The jet component of the impeller-induced flow becomes unstable and shows signs of both sinuous and varicose behavior. The vortex pairs are anchored near the blades, but as they extend outwards into the tank their backbones exhibit time-dependent fluctuation. The instability of the jet is intimately connected with the fluctuation of the tip-vortex system. The time-averaged location of the vortex backbone compares well with previous measurements. The radial profile of θ-averaged radial velocity along the midplane is a good sensitive measure for evaluating the computed results. It is observed that computed flow from the 20 deg oscillatory impeller-induced inflow model compares well with the corresponding experimental measurements on the r-z plane.