[manuc]

Dear all

I am trying to simulate bouyant flow in water with buoyant pimplefoam (dont want Boussinesq foam) as an inital step to simulate flow buoyant flow in water in a container with heating elements inside.

Since chtMultiregionfoam uses a compressible solver, I cant make use of Boussinesq assumption.

What I am left outwith is setting thermophysical properties such that bouyancy is taken into account.
The available options for equation of state being:
equationOfState perfectGas ;//not possible want to use for liquids
rhoConst // not possible need density diff. based convection
perfectFluid //no idea how to specify rho_0 and whether suitable fro bouyancy
icoPolynomial //no idea how to specify the polynomial constants..Where to find them for different fluids



Could someone help to decide on how to approach the problem.

[Tobi]

Dear Manu,

using the known banana trick lead to the following possible models (buoyantPimpleFoam):

Valid rhoThermo types are:

type         mixture                    transport   thermo       equationOfState           specie  energy                  

heRhoThermo  homogeneousMixture         const       hConst       incompressiblePerfectGas  specie  sensibleEnthalpy        
heRhoThermo  homogeneousMixture         const       hConst       perfectGas                specie  sensibleEnthalpy        
heRhoThermo  homogeneousMixture         sutherland  janaf        incompressiblePerfectGas  specie  sensibleEnthalpy        
heRhoThermo  homogeneousMixture         sutherland  janaf        perfectGas                specie  sensibleEnthalpy        
heRhoThermo  inhomogeneousMixture       const       hConst       incompressiblePerfectGas  specie  sensibleEnthalpy        
heRhoThermo  inhomogeneousMixture       const       hConst       perfectGas                specie  sensibleEnthalpy        
heRhoThermo  inhomogeneousMixture       sutherland  janaf        incompressiblePerfectGas  specie  sensibleEnthalpy        
heRhoThermo  inhomogeneousMixture       sutherland  janaf        perfectGas                specie  sensibleEnthalpy        
heRhoThermo  multiComponentMixture      const       hConst       incompressiblePerfectGas  specie  sensibleEnthalpy        
heRhoThermo  multiComponentMixture      const       hConst       incompressiblePerfectGas  specie  sensibleInternalEnergy  
heRhoThermo  multiComponentMixture      const       hConst       perfectGas                specie  sensibleEnthalpy        
heRhoThermo  multiComponentMixture      const       hConst       perfectGas                specie  sensibleInternalEnergy  
heRhoThermo  multiComponentMixture      polynomial  hPolynomial  icoPolynomial             specie  sensibleEnthalpy        
heRhoThermo  multiComponentMixture      polynomial  hPolynomial  icoPolynomial             specie  sensibleInternalEnergy  
heRhoThermo  multiComponentMixture      sutherland  janaf        incompressiblePerfectGas  specie  sensibleEnthalpy        
heRhoThermo  multiComponentMixture      sutherland  janaf        incompressiblePerfectGas  specie  sensibleInternalEnergy  
heRhoThermo  multiComponentMixture      sutherland  janaf        perfectGas                specie  sensibleEnthalpy        
heRhoThermo  multiComponentMixture      sutherland  janaf        perfectGas                specie  sensibleInternalEnergy  
heRhoThermo  pureMixture                const       hConst       Boussinesq                specie  sensibleEnthalpy        
heRhoThermo  pureMixture                const       hConst       Boussinesq                specie  sensibleInternalEnergy  
heRhoThermo  pureMixture                const       hConst       adiabaticPerfectFluid     specie  sensibleEnthalpy        
heRhoThermo  pureMixture                const       hConst       adiabaticPerfectFluid     specie  sensibleInternalEnergy  
heRhoThermo  pureMixture                const       hConst       incompressiblePerfectGas  specie  sensibleEnthalpy        
heRhoThermo  pureMixture                const       hConst       incompressiblePerfectGas  specie  sensibleInternalEnergy  
heRhoThermo  pureMixture                const       hConst       perfectFluid              specie  sensibleEnthalpy        
heRhoThermo  pureMixture                const       hConst       perfectFluid              specie  sensibleInternalEnergy  
heRhoThermo  pureMixture                const       hConst       perfectGas                specie  sensibleEnthalpy        
heRhoThermo  pureMixture                const       hConst       perfectGas                specie  sensibleInternalEnergy  
heRhoThermo  pureMixture                const       hConst       rhoConst                  specie  sensibleEnthalpy        
heRhoThermo  pureMixture                const       hConst       rhoConst                  specie  sensibleInternalEnergy  
heRhoThermo  pureMixture                polynomial  hPolynomial  PengRobinsonGas           specie  sensibleEnthalpy        
heRhoThermo  pureMixture                polynomial  hPolynomial  icoPolynomial             specie  sensibleEnthalpy        
heRhoThermo  pureMixture                polynomial  hPolynomial  icoPolynomial             specie  sensibleInternalEnergy  
heRhoThermo  pureMixture                polynomial  janaf        PengRobinsonGas           specie  sensibleEnthalpy        
heRhoThermo  pureMixture                sutherland  hConst       Boussinesq                specie  sensibleEnthalpy        
heRhoThermo  pureMixture                sutherland  hConst       Boussinesq                specie  sensibleInternalEnergy  
heRhoThermo  pureMixture                sutherland  hConst       PengRobinsonGas           specie  sensibleEnthalpy        
heRhoThermo  pureMixture                sutherland  hConst       incompressiblePerfectGas  specie  sensibleEnthalpy        
heRhoThermo  pureMixture                sutherland  hConst       incompressiblePerfectGas  specie  sensibleInternalEnergy  
heRhoThermo  pureMixture                sutherland  hConst       perfectGas                specie  sensibleEnthalpy        
heRhoThermo  pureMixture                sutherland  hConst       perfectGas                specie  sensibleInternalEnergy  
heRhoThermo  pureMixture                sutherland  janaf        Boussinesq                specie  sensibleEnthalpy        
heRhoThermo  pureMixture                sutherland  janaf        Boussinesq                specie  sensibleInternalEnergy  
heRhoThermo  pureMixture                sutherland  janaf        incompressiblePerfectGas  specie  sensibleEnthalpy        
heRhoThermo  pureMixture                sutherland  janaf        incompressiblePerfectGas  specie  sensibleInternalEnergy  
heRhoThermo  pureMixture                sutherland  janaf        perfectGas                specie  sensibleEnthalpy        
heRhoThermo  pureMixture                sutherland  janaf        perfectGas                specie  sensibleInternalEnergy  
heRhoThermo  reactingMixture            const       hConst       incompressiblePerfectGas  specie  sensibleEnthalpy        
heRhoThermo  reactingMixture            const       hConst       incompressiblePerfectGas  specie  sensibleInternalEnergy  
heRhoThermo  reactingMixture            const       hConst       perfectGas                specie  sensibleEnthalpy        
heRhoThermo  reactingMixture            const       hConst       perfectGas                specie  sensibleInternalEnergy  
heRhoThermo  reactingMixture            polynomial  hPolynomial  icoPolynomial             specie  sensibleEnthalpy        
heRhoThermo  reactingMixture            polynomial  hPolynomial  icoPolynomial             specie  sensibleInternalEnergy  
heRhoThermo  reactingMixture            sutherland  janaf        incompressiblePerfectGas  specie  sensibleEnthalpy        
heRhoThermo  reactingMixture            sutherland  janaf        incompressiblePerfectGas  specie  sensibleInternalEnergy  
heRhoThermo  reactingMixture            sutherland  janaf        perfectGas                specie  sensibleEnthalpy        
heRhoThermo  reactingMixture            sutherland  janaf        perfectGas                specie  sensibleInternalEnergy  
heRhoThermo  singleStepReactingMixture  sutherland  janaf        perfectGas                specie  sensibleEnthalpy        
heRhoThermo  singleStepReactingMixture  sutherland  janaf        perfectGas                specie  sensibleInternalEnergy  
heRhoThermo  veryInhomogeneousMixture   const       hConst       incompressiblePerfectGas  specie  sensibleEnthalpy        
heRhoThermo  veryInhomogeneousMixture   const       hConst       perfectGas                specie  sensibleEnthalpy        
heRhoThermo  veryInhomogeneousMixture   sutherland  janaf        incompressiblePerfectGas  specie  sensibleEnthalpy        
heRhoThermo  veryInhomogeneousMixture   sutherland  janaf        perfectGas                specie  sensibleEnthalpy

As you see and already mentioned is the polynomial function. Here we simple define the temperature depended density polynomial (up to 7th order). I can not see the problem you have with the polynomial stuff? These coefficients are not tablulated and stored somewhere. For example, if you have data for your fluid, just build a polynomial of n-th order (like 4th) that matches your results and then you have the polynomial functions. Normally we build the polynom with the least squares method.

[manuc]

Dear Tobi

I was interested in how the polynomial is calculated. For example, if my fluid is molten metal, for which I don't have any data for temp distribution how can I fit the polynomial.

[wangchengan2003]

Dear Tobi
I want to know set the polynomial properties in other solvers? For example, in IcoFoam, PimpleDymFoam, etc?
Best regards

[Tobi]

Hi guys,

your questions are funny, especially yours manu
You have to give openfoam the polynomial, I mean the polynomial coefficients. If you have no data then how should you get the coefficients? There is no way and the toolbox need to know the function (finally the value of rho, mu etc).

@wang... you have two options. Either you implement the polynomial function library to the solver or you just modifiy your solver by hand and manipulate the needed values using the polynomial function. Example given. Instead of using a constant mu in icoFoam, you have to make a scalarField for mu, and update mu based on your polynomial. Keep in mind that here you also have to add the temperature equation if the quantities are temperature depended.

[manuc]

Dear Tobi

I know my question makes no sense . What I wanted to know was is there any function which calculates the coefficents by intself from material properties or so. When I read on the polynomial fit you mentioned I understood , its not possible. So what I tried was to go with boussinesq assumption for multiregiondomain. I merged some existing solvers to create one with natural convection effects included
http://www.cfd-online.com/Forums/ope...tml#post625227

If you have any suggestions on it would be great.

[Tobi]

Originally Posted by manuc

Dear Tobi

What I wanted to know was is there any function which calculates the coefficents by intself from material properties or so.

I don't get the point. Finally you want to calculate a material quantity like the conductivity. Here you can derive that one from other material quantities but still you need them. If you think about gases or liquids under special conditions you can check out the gas kinetics. There are complex calculations for thermal conductivity, density, heat capacity etc. But finally I am not sure if someone from CFD uses that to calculate something. In my opinion I am not sure if you can use the gas kinetic equations for liquid melt which cool down fast. Either you have the measurements and the data or not

The gas kinetic equations are used in combustions (I also used them).

[manuc]

Dear Tobi
I want to study natural and mixed convection in fluid with bottom heated top cooled arrangement with different material solid sphere ( Al or copper, ceramics) inside the domain.
I need a multiregion solver for it. I tried withchtmultiregionfoam which works fine for perfect gas I need to try it for different fluids of different Pr for which it would be difficult to get the equation. (So I dropped the idea of polynomial fit)
So I moved to a solver with boussinesq assumption where everything is based on material property and coefficient of volume expansion can be varied easily just as function of non dimensional numbers and delta temp.

[Tobi]

You should know that the Boussinesq approximation is only valid within a small temperature range. For air it is round about 30 - 40K with some acceptable error and for liquid (water) i think it was 5 - 10 K with some acceptable error (error was 2-5%). If you have higher dT its inaccurate. But its your decision. The values and erros should be somewhere in Ferziger and Perić chapter 1. So be aware that if you have strong cooling or heating, your assumption will fail and you will get wrong stuff based on the fact that you are using a non physical model.

[manuc]

Dear Tobi

My range of investigation is limited to beta*deltaT<<1 where boussinesq is valid

[wangchengan2003]

Thank you very much for you help ,Tobi