Chapter 34 - Comparison of CFD Methods for Modelling of Stirred Tanks

Abstract

Simulation by computational fluid dynamics (CFD) is becoming an increasingly useful tool in analysis of the flow in mechanically stirred tanks. However, the development of accurate and efficient modeling methods is a continuing process. One significant complication in modeling of baffled stirred tanks is accounting for the motion of the impeller, since there is no single frame of reference for calculation. A number of approaches have been taken to this problem. In some cases an empirical model is provided for the impeller, whereas other methods are capable of predicting the effect of the impeller directly. In the latter category are the Sliding Mesh and Multiple Frames of Reference (MFR) methods. Results are presented for simulation of a standard configuration tank stirred by a Rushton turbine. Using the same geometry and finite volume grid, the fluid flow is simulated using both these methods. The Sliding Mesh and MFR methods are discussed and compared with respect to computation time and accuracy of prediction of mean velocities and turbulence parameters. It is found that the MFR method provides a saving in computation time of about an order of magnitude. Predicted mean velocities using both methods are compared with experimental data, and it is found that both methods provide good agreement with experimental data. Turbulence parameters are also compared with experimental data. It is found that both methods significantly underpredict the values of specific turbulent kinetic energy and rate of dissipation of turbulent energy.