# Can anybody please check my boundary conditions?

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 August 3, 2011, 09:06 #41 New Member   BR Join Date: May 2009 Posts: 23 Rep Power: 17 do you use simpleFoam? did you try to do without turbulence models?

 August 3, 2011, 09:08 #42 Senior Member   lore Join Date: Mar 2010 Location: Italy Posts: 460 Rep Power: 18 I only tried simpleFoam with turbulence models.

 August 3, 2011, 09:10 #43 New Member   BR Join Date: May 2009 Posts: 23 Rep Power: 17 First : Try using no turbulence model. It will be easier to debug. Second : I cant understand why your k value is 0 everywhere and epsilon value is 1.78 ?? Any particular reason behind this?

August 3, 2011, 09:13
#44
Senior Member

lore
Join Date: Mar 2010
Location: Italy
Posts: 460
Rep Power: 18
Quote:
 Originally Posted by Balakrshnan Ramakrishnan First : Try using no turbulence model. It will be easier to debug. Second : I cant understand why your k value is 0 everywhere and epsilon value is 1.78 ?? Any particular reason behind this?
Nope, no reason, just copied them over from the motorbike tutorial. Anyway setting the boundary as srakshit I now got some reasonable results!

Thank you to both of you!

 August 3, 2011, 09:17 #45 New Member   BR Join Date: May 2009 Posts: 23 Rep Power: 17 Just for your reference in the future simulations please look into http://www.cfd-online.com/Wiki/Turbu...ary_conditions to set initial conditions for k , epsilon and omega.. Have fun

 August 3, 2011, 11:23 #46 Senior Member   lore Join Date: Mar 2010 Location: Italy Posts: 460 Rep Power: 18 Thank you!

August 3, 2011, 22:53
#47
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Sukanta Rakshit
Join Date: Jun 2009
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Quote:
 You have to define one pressure value at least. I set the pressure value to 0 at the inlet and the rest as you suggested. Now it's running, let's see what comes out.
Out of pressure and velocity you can define one. If you have defined velocity at inlet and outlet as 30 m/s, then i wont prefer setting pressure = 0.

This is because of 2 reasons
1. If at the outlet U is fixed at 30 m/s, pressure will be depend on what fluid you are using. At steady state, both inlet and outlet pressure should be in the same range (not much difference) because its constant velocity simulation.
2. If U and p are inconsistent then you will get inconsistent solution. More iterations you will run, higher the velocity inside the domain you will get. This is because flow will bounce between two Dirichlet boundaries with inconsistent pressure.

If you are thinking of setting pressure in either of the boundary, then you have to keep the velocity floating at that boundary (or you should define some physical value).

Results with flow over a cylinder with fixed velocity (U=30 m/s) and floating pressure can be seen in the attached images.

Yes, i agree with Ramakrishnan. Turbulent properties should be defined correctly and solving without them will help in identifying the problem.
Attached Images
 freeStreamPressure.jpg (16.9 KB, 18 views) zeroGradient.jpg (15.3 KB, 15 views)

 August 4, 2011, 06:58 #48 Senior Member   lore Join Date: Mar 2010 Location: Italy Posts: 460 Rep Power: 18 The same case won't converge with icoFoam… Why?

August 4, 2011, 19:40
#49
New Member

Sukanta Rakshit
Join Date: Jun 2009
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Quote:
 Originally Posted by lovecraft22 The same case won't converge with icoFoam… Why?
It does, try decreasing the deltaT.

Also, check your ddtSchemes in fvSchemes.

 August 5, 2011, 04:24 #50 Senior Member   lore Join Date: Mar 2010 Location: Italy Posts: 460 Rep Power: 18 What should I check about the ddtSchemes?