Trailing vortices generated by a Rushton turbine: Assessment of URANS and large Eddy simulations

The discharge flow of a Rushton turbine is characterized by the formation of coherent vortex structures induced by the blade motion and called trailing vortices. The objective here is to assess the ability of computational fluid dynamics (CFD) to represent the trailing vortices and their relationship with turbulence properties. To this end, two simulations have been realized: an unsteady Reynolds-Averaged Navier-Stokes (URANS) simulation and a Large Eddy Simulation (LES) simulation. The trajectory of the trailing vortices predicted by the simulations has been compared with previous works. This comparison shows that the URANS simulation does not predict properly the trailing vortices while the LES results are very close to the experimental ones. As a consequence, the turbulence properties spatially correlated to the trailing vortices are well predicted by LES but not by URANS simulation.