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-   -   About default blockage material(198) (http://www.cfd-online.com/Forums/phoenics/51204-about-default-blockage-material-198-a.html)

H.P.LIU May 30, 2001 06:17

About default blockage material(198)
 
According to the TR326 PHOENICS-VR Reference Guide,The default blockage material(198),Solid with smooth-wall friction,can prevent flow within itself and any heat transfer. In effect, any region occupied by such a blockagy does not exist as far as the calculations are concerned. However, when I place three blockages(198) which are combined to an inlet passage into the fluid and simulate the fluid flow and heat transfer in the calculation domain, to my surprise, I find that the nodal temperature located at the blockages and near blockage material isn't obviously correct. It is shown that blockage material participates the heat transfer and is related to heat transfer calculations. How can I explain the error nodal temperature (in the blockage and near the the blockage) which results from the blockage(198) and avoid it?

Kike May 30, 2001 09:00

Re: About default blockage material(198)
 
Hi, HPLiu

Here I send you some hints. Have you check there are no radiation model activated "by accident" or "by default"?

Have you check you have iniadd=f into Q1 file (Group 11)? When you work with crossing solid regions, the PRPS indexes could be added and you will have another material (not 198) instead of the smooth solid. If you insert this flag the values of PRPS (nor any calculated or stored magnitude) will not be added if they are defined twice.

Why the temperature isn't correct near the walls? Why do you think it shows that the solid surfaces are participating?

Have you check into the Q1 file to see if you have any source term (patch in Group 13) declared on the solid surfaces? If not, the solid surface do not interchange energy with your flow.

When you put a solid into a flow region PHOENICS multiplies by zero the coefficients in every face of those cells declared by the "patch" which defines the solid region. So you have no transfer of mass or energy into nor out the solid surface.

Do you have boundary layers on the solid surfaces?, Compressible flows over the solids? What is the dependency between the density, pressure and temperature for your fluid?

Regards

Kike

H.P.Liu June 3, 2001 07:08

Re: About default blockage material(198)
 
Hi, Kike: Thank for your help, some problem mentioned by you is explained as follows: I have check there are no radiation model activated "by accident" or "by default"? Iniadd=F is set in Q1 file(Group 11) Since surface temperature is set as one source term declared on the solid (198) surfaces. the solid surface should interchange energy with fluid flow according to PHOENICS polis. but nothing has happed as if adiabctic condtion is added and the temperature in the solid cell and near solid cell is obviously deviated from the normal value. If the solid region is set as adiabatic, the incorrect temperature is also present in the solid cell and near cell.This is the reason I think the solid cell particapates the heat transfer. Boundary layers on the solid surfaces is ignored and incompressible flows N-s equation is considered.

Kike June 5, 2001 09:03

Re: About default blockage material(198)
 
Hi, HPLui

In this case I recommend you to go step by step, ie. simplify your domain. Try to create a single square domain with only a solid block inside. See what happen if you use the same eqs. and models. Sometimes it is better to put the hole problem piece by piece and see which is the "troubler piece".

I do not use VR Editor (nor Viewer), I prefer the "crude" Q1 strategy and clear things in front of me. Try to skip the formulation of VR to run your simplified test cases, ie. define your solids objects via blocked cells and PRPS or walls. Good luck

Kike

David Glynn June 18, 2001 10:11

Re: About default blockage material(198)
 
I don't understand exactly what you are doing, but it is definitely the case that nothing is solved in a blockage comprised of material 198.

Try setting up some simple cases with VR as examples.

However, DON'T set your domain material to be 198, and then "drill holes" in it using objects with a fluid material index. If you have flow present, the domain material has to be a fluid material.


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