# Can laminar model simulate flow with Re=20000

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 November 10, 2005, 14:30 Can laminar model simulate flow with Re=20000 #1 Baicang Guest   Posts: n/a Hello, I want to know that if laminar model can simulate flow with Reynolds number up to 20000, a free surface exists in my calculation case. Thanks in advance!

 November 14, 2005, 12:14 Re: Can laminar model simulate flow with Re=20000 #2 Evan Rosenbaum Guest   Posts: n/a Sure, it will just simulate it as laminar.

 November 14, 2005, 12:57 Re: Can laminar model simulate flow with Re=20000 #3 Baicang Guest   Posts: n/a Would you like to explain it more concretely? By now I introduce a const eddy viscosity Reynolds number to the whole computation domain,and a reasonable result is obtained.A simple turbulent model is adopted in this way. How do you think it? Thanks very much for your discussion.

 November 15, 2005, 10:49 Re: Can laminar model simulate flow with Re=20000 #4 Jeremy Guest   Posts: n/a What Evan is saying is that you can always use a laminar model and it will give you results. The results may not accurately predict the 'real' situation, but it would predict a turbulent free situation. For example, you could simulate simple pipe flow with a laminar model for a Reynolds number of 50 000. Would the results mean anything? For most practical purposes, at such a high Reynolds number the flow should be turbulent, however there have been some very carefully performed experiments were laminar flow in straight pipes have achieved Reynolds numbers in the 10s of thousands, but those are under very special conditions with very smooth pipe walls and minimal vibrations of the pipe and so forth. Any small perturbation of the flow would quickly send it into a turbulance. Can a Reynolds number of 20 000 be used in your case? Possibly, but to figure this out you are best to check the literature for similar situations. Has there been experimental work done on the same geometry? Is there any published data to indicate when the onset of transition begins? Someone on this forum might know the answer to this, but you would probably have to give a better description of the geometry and flow in order to evaluate your situation.

 November 17, 2005, 11:39 Re: Can laminar model simulate flow with Re=20000 #5 Baicang Guest   Posts: n/a Thanks for Evan and Jeremy's help Now I adopt a const eddy viscosity in the whole computational domain, it means I employ a very simple turbulent model to solve my problem, the results show that this method is feasible. Although this method isn't as good as k-epsilon model, it can save a lot of computational time. How do you think this strategy? Baicang