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Old   September 5, 2013, 06:19
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Originally Posted by dinesh View Post
With SIMPLE and PRESTO i also got the convergence.
If so, why are you using PISO and Body Force Weighted?

I think the problem is not using SIMPLE or PISO / PRESTO! or B.F.W.
Reduce all under relaxation factors to 0.5. Finer meshes or smaller time steps also may provide a converged solution.

Have you tried SST k-w instead of k-e?
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Old   September 5, 2013, 12:09
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Originally Posted by r.mojtaba View Post
If so, why are you using PISO and Body Force Weighted?

I think the problem is not using SIMPLE or PISO / PRESTO! or B.F.W.
Reduce all under relaxation factors to 0.5. Finer meshes or smaller time steps also may provide a converged solution.

Have you tried SST k-w instead of k-e?
I am trying to validate my model with the "shumeli model" with gives the comparision of these two models.
Also the reason of using k ep model is that it has enhanced wall function,My model contains circular fins. so i went with that.
Reducing the URF helps in convergence but i thk we must not alter these values as they effect the results.
Can you suggest about some rule for governing the grid size?
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Old   September 6, 2013, 05:57
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Originally Posted by dinesh View Post
the reason of using k ep model is that it has enhanced wall function,My model contains circular fins. so i went with that.
k-ep is a very inaccurate model for near wall regions. The standard turbulence model for general purpose simulations is SST k-w. You can find the reasons in any up to date turbulence text and in CFX documentations, too.

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Originally Posted by dinesh View Post
Reducing the URF helps in convergence but i thk we must not alter these values as they effect the results.
Changing URFs affects the way the solution converges, but after achieving a converged solution (small enough residuals, with monotonic residual curves) it doesn't matter how you've done it. Generally speaking, reducing URFs provide a better convergence, but more run time is required.

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Originally Posted by dinesh View Post
Can you suggest about some rule for governing the grid size?
Start with a coarse mesh and make it finer and finer till the results are not changed (Grid Independency Test)
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Old   September 9, 2013, 07:23
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Quote:
Originally Posted by r.mojtaba View Post
k-ep is a very inaccurate model for near wall regions. The standard turbulence model for general purpose simulations is SST k-w. You can find the reasons in any up to date turbulence text and in CFX documentations, too.


Changing URFs affects the way the solution converges, but after achieving a converged solution (small enough residuals, with monotonic residual curves) it doesn't matter how you've done it. Generally speaking, reducing URFs provide a better convergence, but more run time is required.


Start with a coarse mesh and make it finer and finer till the results are not changed (Grid Independency Test)
Dear Sir
Can you suggest: while using Boussinesq parameter under operating condition menu, what should be the operating temperature and operating density. (Should it be The melting temperature and the solid state density of phase change material or something else)
Also plz suggest, since we have in governing equation additional source terms in the momentum and energy equations, so how do we calculate these values. Regarding input in the fluent there is option under cell zone conditions/ checking the source terms enable us to enter these values of mass, momentum, energy source term. But how do I calculate it from governing PDE.
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Old   September 10, 2013, 07:50
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Originally Posted by dinesh View Post
while using Boussinesq parameter under operating condition menu, what should be the operating temperature and operating density. (Should it be The melting temperature and the solid state density of phase change material or something else)
An estimation of operating temperature can be the average of maximum and minimum temperatures in system. This is also applicable for density.

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Originally Posted by dinesh View Post
how do we calculate these values. Regarding input in the fluent there is option under cell zone conditions/ checking the source terms enable us to enter these values of mass, momentum, energy source term. But how do I calculate it from governing PDE.
When you enable Solidification model in Fluent, related source terms are implemented into equations automatically. You need not to import anything.
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