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.

[1]  J. Derksen,et al.  Three-dimensional LDA measurements in the impeller region of a turbulently stirred tank , 1999 .

[2]  Jinhee Jeong,et al.  On the identification of a vortex , 1995, Journal of Fluid Mechanics.

[3]  Michael Yianneskis,et al.  Direct determination of energy dissipation in stirred vessels with two‐point LDA , 2005 .

[4]  S L Yeoh,et al.  Numerical Simulation of Turbulent Flow Characteristics in a Stirred Vessel Using the LES and RANS Approaches with the Sliding/Deforming Mesh Methodology , 2004 .

[5]  Carl M. Stoots,et al.  Mean velocity field relative to a Rushton turbine blade , 1995 .

[6]  K. Van't Riet,et al.  The trailing vortex system produced by Rushton turbine agitators , 1975 .

[7]  Alain Liné,et al.  Characterization of Trailing Vortices Generated by a Rushton Turbine , 2004 .

[8]  Michael Yianneskis,et al.  Turbulence properties of the impeller stream of a Rushton turbine , 1998 .

[9]  J. Derksen,et al.  Assessment of large eddy and RANS stirred tank simulations by means of LDA , 2004 .

[10]  Jérôme Morchain,et al.  Evaluation of local kinetic energy dissipation rate in the impeller stream of a Rushton turbine by time-resolved PIV , 2009 .

[11]  Alain Liné,et al.  Experimental analysis of hydrodynamics in a radially agitated tank , 2002 .

[12]  Vivek V. Ranade,et al.  An efficient computational model for simulating flow in stirred vessels: a case of Rushton turbine , 1997 .

[13]  Gary B. Tatterson,et al.  Fluid mixing and gas dispersion in agitated tanks , 1991 .

[14]  Wei-Ming Lu,et al.  Effect of blade pitch on the structure of the trailing vortex around rushton turbine impellers , 1998 .

[15]  Ronald Adrian,et al.  PIV study of small‐scale flow structure around a Rushton turbine , 2001 .

[16]  Jos Derksen.  Assessment of Large Eddy Simulations for Agitated Flows , 2001 .

[17]  Michael Yianneskis,et al.  Observations on the Distribution of Energy Dissipation in Stirred Vessels , 2000 .

[18]  Michael Yianneskis,et al.  The Influence of Rushton Impeller Blade and Disk Thickness on the Mixing Characteristics of Stirred Vessels , 1996 .

[19]  M. Schäfer,et al.  Turbulence generation by different types of impellers , 2000 .

[20]  Michael Yianneskis,et al.  An experimental study of the steady and unsteady flow characteristics of stirred reactors , 1987, Journal of Fluid Mechanics.

[21]  Jos Derksen,et al.  Large eddy simulations on the flow driven by a Rushton turbine , 1999 .

[22]  J. Morchain,et al.  LES and URANS simulations of hydrodynamics in mixing tank: Comparison to PIV experiments , 2008 .