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-   -   Flow around the microscale tube in CFX4.4 (http://www.cfd-online.com/Forums/cfx/20046-flow-around-microscale-tube-cfx4-4-a.html)

hsinluen December 10, 2003 05:13

Flow around the microscale tube in CFX4.4
 
Dear Sir,

I conduct the flow simulation around the micro-scale tube with diameter 100 micro meter. In this scale, belongs to the continum flow range. In build/analysis, I set the geometry scale factor 1.0e-6, the pressure field could not be predicted correctly. In the same condition, I don't set the geometry scale factors, the pressure distribution around the tube is predicted correctly.

My question is whether CFX 4.4 could simulate the flow in micro scale which is in the continum range.

If Yes, please tell me any tricks in simulating the micro-scale flow around the tube.

Thank you for your kindest help.

Glenn Horrocks December 10, 2003 17:22

Re: Flow around the microscale tube in CFX4.4
 
Hi hsinluen,

By "continuum range" I assume you mean laminar flow, and probably stokes flow where the inertial effects are negligible.

CFX4.4 can handle this type of flow. In fact you should find convergence very fast as there should be no seperations. Make sure you turn turbulence off by setting the turbulence model to laminar.

I don't know why you are having the difference with the scale factors in Build. Can you explain a bit more please?

Glenn

Jeff December 10, 2003 21:53

Re: Flow around the microscale tube in CFX4.4
 
Try,

1. Laminar flow (as suggested). 2. Make sure Pref is atmospheric and all pressure boundaries are relative (i.e. zero). At that scale you'll likely have very little pressure drop from cell to cell. You don't want to swamp out the precision with a large boundary pressure. 3. Run it in double precision, just in case the roundoff is killing the continuity equation.

Jeff


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