Multiple Reference Frames Model

To simulate turbulent flows, Reynolds-averaged Navier-Stokes (RANS) equations form the basis for most codes. Several turbulence models are usually provided. A new turbulence model may also usually be incorporated via user-defined routines. Recently, many of the commercial CFD codes have announced the inclusion of large eddy simulation (LES) capabilities. Considering the importance of rotating equipment used in reactor engineering applications, the ability to handle multiple reference frames or sliding meshes is important. Most leading commercial CFD codes provide... 

FIGURE 10.3 Approaches to modeling flow in stirred reactors, (a) Black box approach, (b) sliding mesh approach, (c) multiple reference frame or inner-outer approach, (d) snapshot approach. 

Ranade, V.V, Tayaliya, Y. and Choudhury, D. (1997), Modeling of flow in stirred vessels comparison of snapshot, multiple reference frame and sliding mesh approaches. Presented at 16th NAME Meeting, Williamsberg, June 22-21. 

Assessment of Multiple Rotating Reference Frame Model Simulations... 

Preprosessing and grid generation was done with the commercial Fluent Gambit 1.3. The CFD code Fluent 5.5 was used in the simulation. Standard k-e turbulence model and standard wall functions were used. Multiple reference frame method was used in all simulations instead of the computationally slower sliding mesh method. Simulations were done in one phase (t). 

For symmetry reasons it was sufficient to model only a part of the domain. The smallest symmetry of the geometry is 60 which contains one impeller blade and one vertical baffle. Two different type of grids were studied. Both grids were refined adaptively. After adaption both grids had about 450 000 cells. Steady state multiple reference frame approach was used in Fluent 5.5 simulations for modelling the rotor rotation in the stationary tank. Standard k-e turbulent model and standard wall functions were used. Simulations were done in liquid (water) phase. 

A 60 sector of the tank was modelled with periodic boundaries on the sides of the sector and symmetric boundary on the top of the tank to describe the free surface. Standard wall functions were employed on all wall boundaries of the computational domain. Huent s multiple reference frame steady state approach was used with k-e turbulence model. Calculation was done in one phase (water). 

The particle tracking-based advective control model described in this chapter is capable of solving two- and three-dimensional plume capture problems with multiple candidate wells and multiple particles in confined and unconfined aquifers. The formulation provides a direct approach to solving plume control problems and uses both forward and reverse particle tracking to exploit numerical characteristics of the two reference frames. 

Fig. 7.22. A representative grid employed for the multiple rotating reference frame (MRRF) model simulations.

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