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west_wing August 25, 2003 10:00

How to solve another continuum and momentum eqn?
How to solve another continuum and momentum equation in FLUENT? Our research group develops some new turbulent model. In this model, I must solve two momentum equations and two continuum equation. There are pressure gradient in every momentum. All the equation writes as follow (steady flow):

Divergence (Uaverage)=0 (1)

Convection(Uaverage) = Diffusuion(Uaverage)+Gradient(Paverge)+Source (2)

Divergence (Uflucture)=0 (3)

Convection(Uflucture)=Diffusuion(Uflucture)+Gradie nt(Pflucture)+Source (4)

Other algebraic equations (5)

Where: U=Uaverage+Uflucture P= Paverge+ Pflucture

There are eight different equations and eight variables (Uaverage, Vaverage, Waverage, Paverage, Uflucture, Vflucture, Wflucture, Pflucture) for 3D. For FLUENT, the first pressure ,i.e. Paverge can be coupled with velocity through SIMPLE algorithm or by using couple solve. With UDS equation supplied by FLUENT, I can solve three component of Uflucture by view every component as scalar. But the Pflucture caní»t be solved through an independent scalar equation. I caní»t modify the solve process of FLUENT, so the Pflucture caní»t be revised through continuum equation or be solve simulate with other equation. One method is that take divergence for equation (4), then we can get a Poisson equation about Pflucture. Many related items appears in equation (4) will be removed owing to the continuum limitation (eqn.3). Then I can regard Pflucture as an independent variable (scalar),.the origin four difference equations(Uflucture, Vflucture, Wflucture, Pflucture) will become four scalar equations which FLUENT can solve. But in the new equation, source will be more complex. And I caní»t know exactly whether there are other problems with this solve process.

Some one can give good idea about this problem? Any opinion is welcome!

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