Large eddy simulations of the turbulent flow in a stirred reactor

Large eddy simulations of a;baffled reactor stirred with a single Rushton turbine were performed. The turbine was positioned at mid-height in the reactor. The unsteady spatially filtered incompressible Navier-Stokes equations have been solved numerically. These large eddy simulations (LES) provide details of the flow field that cannot be obtained with the so-called Reynolds averaged equations and corresponding models. The un-resolved scales have been modelled implicitly through the truncation errors of the discretisation; The motion of the blades was described as time-dependent momentum sources. The time-averaged flow properties, mean flow and turbulence, have been studied. Phase averaging was used to characterize the flow relative to the impeller blades. Power spectral density and correlations, both in time and space were investigated. The results have been compared-with the experimental data from several sources and also with the data from other simulations. Comparing our data with measurements we see an overall good agreement both qualitatively and quantitatively. In the impeller stream we;observe an acceleration of the flow in the radial direction due to the trailing vortex pair. This acceleration can also be deduced from published experimental and numerical data. There are however some discrepancies concerning velocity fluctuations in the impeller area. These discrepancies are probably caused by inaccuracy in the impeller description. (C) 1998 Elsevier Science Ltd. All rights reserved.