Large-Eddy Simulation of Turbulent Flows in Baffled Stirred Tank Reactors

Abstract

Baffled stirred tank reactors are frequently used in the (petro)chemical industry for mixing purposes and detailed information on the (time-dependent) flow patterns and turbulence statistics in such reactors is important for an optimal design. The flow in these systems is highly unsteady and in particular near the turbine, quasi-periodic fluid motion can be observed. Since large-eddy simulation (LES) is inherently a time-dependent technique, this unsteady and quasi-periodic behavior of the flow is accounted for in a natural way. This is part of the motivation to use LES to this kind of flow configurations instead of the usual approach based on Reynolds-averaged Navier-Stokes (RANS) methods. In addition, the use of LES is supported by the complexity of the flow. In the reactor, and in particular near the turbine, the swirling motion of the flow is strong. Furthermore, a ‘jet-like’ behavior of the flow occurs near the turbine with impingement of the jet at the reactor wall. At the baffles, flow separation takes place which results in recirculation zones behind the baffles. All these phenomena occur simultaneously in the reactor.