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Damping Factor too small

Posted 15.04.2010, 08:44 GMT-4 5 Replies

Arun Thomas
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Hi

I am trying to simulate the wind flow past a cylinder of dimension 0.00084m as radius and with density 1.23 and viscosity as 1.85e-5. Using the property of similutde when i scaled down to this dimensions given above,but then my velocity has to be 500m/s.

When I solve using SPOOLES as the solver. I got the errror " Damping Factor too Small.Returned solution has not converged". I am not so familiar with these terms.But if I run with a lower velocity like 1m/s I get a good solution.

Can we use comsol only to small parameter problems.

Please let me know what can be done to solve this problem.

Best Regards

Thomas
5 Replies Last Post 16.04.2010, 08:14 GMT-4
Danial Tz
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Posted: 2 decades ago 15.04.2010, 10:16 GMT-4
What is the Reynolds number (with respect to the diameter of the cylinder) you are trying to achieve?

If it is higher than 1000-2000 you will need special treatments with nearly everything in Comsol.
What is the Reynolds number (with respect to the diameter of the cylinder) you are trying to achieve? If it is higher than 1000-2000 you will need special treatments with nearly everything in Comsol.
Arun Thomas
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Posted: 2 decades ago 15.04.2010, 10:51 GMT-4
Hi Danial

Thank you for replying to my problem.

My dimensions are diamter of cylinder 0.168m with 5 m/s velocity ,density of air 1.23 and viscosity of 1.85e-5.

So when i calulate it Reynolds number its realy very high, arounf 56,000. Does that mean I cannot solve this problem?

Thanks for helping.

Best Regards
Thomas

Hi Danial Thank you for replying to my problem. My dimensions are diamter of cylinder 0.168m with 5 m/s velocity ,density of air 1.23 and viscosity of 1.85e-5. So when i calulate it Reynolds number its realy very high, arounf 56,000. Does that mean I cannot solve this problem? Thanks for helping. Best Regards Thomas
Danial Tz
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Posted: 2 decades ago 15.04.2010, 11:22 GMT-4
I do not have an answer to whether it is possible or not.

You should take care of turbulence, either using Turbulent models inside the Comsol, i.e. k-e model if you want to just simulate the general flow behaviour. Otherwise if you want to resolve the eddies and vortices behind the cylinder, I am not sure if you can do it with the methods available in Comsol. In that case I can imagine you go with methods like LES to resolve the eddies at high Re's.

I do not have an answer to whether it is possible or not. You should take care of turbulence, either using Turbulent models inside the Comsol, i.e. k-e model if you want to just simulate the general flow behaviour. Otherwise if you want to resolve the eddies and vortices behind the cylinder, I am not sure if you can do it with the methods available in Comsol. In that case I can imagine you go with methods like LES to resolve the eddies at high Re's.
Arun Thomas
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Posted: 2 decades ago 16.04.2010, 07:57 GMT-4

Hey Daniel

Thanks for the tip.It worked!

I just wanted to simulate the flow past a cylinder.Now I got great simulation with turbulences.
Hey Daniel Thanks for the tip.It worked! I just wanted to simulate the flow past a cylinder.Now I got great simulation with turbulences.
Danial Tz
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Posted: 2 decades ago 16.04.2010, 08:14 GMT-4
great to hear it works!
great to hear it works!

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