282309 Investigating On the Influence of Mesh Density, Turbulence Models and Numerical Aspects of CFD Modeling in PBT Impellers Using Non-Structured Meshes

Wednesday, October 31, 2012: 2:10 PM
Frick (Omni )
Josť Roberto Nunhez, Chemical Process Department, UNICAMP, Campinas, Brazil, Suzanne Kresta, University of Alberta, Edmonton, AB, Canada, Nicolas Spogis, ESSS, Sao Paulo, Brazil, Marcio Bezerra Machado, Chemical and Materials Engineering, University of Alberta, Edmonton, AB, Canada and Josť L. Gomez, School of Chemical Engineering, State University of Campinas, Campinas, Brazil

The use of non-structured meshes has received recently considerable attention for discretization of the computational domain in CFD simulations (Vakili and Esfahany, 2009; Cabrales, et al., 2011). The non-structured meshes (the most common are tetraedrals) allow adequate adaptation of irregular geometries and easy use of automated algorithms for mesh generation in most commercial CFD software. It has been consistently suggested in the literature that hexaedrical meshes are preferred over tetraedrals. However, they can be used, provided that some care is taken to provide a good representation of the physical phenomena of the problem. Recently published works have been proving that if they are used with care, satisfactory results are obtained (Spogis, 2007). Most of works developed with the use of CFD simulation for mixing processes use hexaedrals and to date tetraedrals do not have the same acceptance of hexaedrals  (Joaquim, et al., 2007) and part of this work is aimed at showing that they can provide good results when simulating mixing processes. 
Another objective of this work is to show the effect of mesh refinement in tetrahedrical meshes. It is investigated the influence of the prismatic elements near wall on global parameters such as the Power and Flow numbers. An initial analysis of the sensitivity of some turbulence models and the discretization scheme on the flow field produced were also carried out in this work. In addition, simulations with different mesh resolutions, height and number of elements near the wall were made using different turbulence models (Standard k-ε model, the shear stress transport (SST) and RNG k-ε model) and using the multiple reference frame (MFR) approach. The discretization schemes were limited to upwind and blend factor, since other schemes do not work well with tetraedrals. The commercial  CFD software CFX 13.0 was used to simulate  the results. A pitched blade turbine impeller (PBT 45° down-pumping), was simulated in turbulent flow.
The results obtained for the Power and Flow numbers, the axial velocity profile component of the model in CFD are discussed and compared with experimental data. The velocity was measured using the PIV technique. (Particle Image velocimetry data). A significant influence of some parameters is observed on the determination of some important mixing . In general, the predictions of the velocity profile are influenced in some way by the resolution of the mesh, turbulence model and the discretization.scheme.

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See more of this Session: The Use of CFD In Simulation of Mixing Processes
See more of this Group/Topical: North American Mixing Forum