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-   -   Setting relaxationsfactors (http://www.cfd-online.com/Forums/fluent/27805-setting-relaxationsfactors.html)

Phil July 27, 2000 12:03

Setting relaxationsfactors
 
I try to investigate a flow (water) between two corrugated plates (isotherm), mass flow inlet, pressure outlet and I found out that my solution converges only when my relaxationfactor for momentum is very small (=0.01). I'm using Simplec algorithm for the pressure velocity coupling. It's a steady-state 3d simulation and I use the segregated implizit solver. The flow is laminar. I tried to solve it with values which are closer to the default values in Fluent, but then I don't reach convergence.The change of the underrelaxationsfactors of the pressure has no influence, so I set them as default values.

Any ideas

Phil

Rüdiger Schwarze July 27, 2000 13:07

Re: Setting relaxationsfactors
 
Hi Phil - I've just answered Your mail.

Sung-Eun Kim July 27, 2000 20:35

Re: Setting relaxationsfactors
 
If the fluid is water and you're modeling the flow as laminar, chance is that the flow you're modeling is transient.

Try to model it as a transient flow.

karim July 28, 2000 04:17

Re: Setting relaxationsfactors
 
hi,

why don't you try the segregated solver, your flow regime is laminar, and your fluid is incompressible

Clinton Lafferty July 28, 2000 12:11

Re: Setting relaxationsfactors
 
Do your residual values level-off after several iterations? If so, this may denote an unstable flow field.

John C. Chien July 28, 2000 20:21

Re: Setting relaxationsfactors
 
(1). Flow through a channel with wavy walls, will generate many separation bubbles depending on the Reynolds number. (2). You can start with low Reynolds number case, say Re=10. And then move up to Re=100, 200, 400, 1000 and so forth. (3). In this way, you will be able to see the flow pattern. (4). If you run into flow separations, then the flow will start to oscillate by changing the separation pattern on two wavy walls. In this case, above this Reynolds number, you need to simulate the transient flow. (it still possible to obtain steady state solution, if you use symmetry condition and solve only a half of the flow field.

Ray July 31, 2000 05:01

Re: Setting relaxationsfactors
 
Hi, John,

I am interested in the wavy wall channel flows. I am simulating channel flow in a oscillatory baffled reactor. What's your suggestion for the transient flow simulation? Should I turn on the turbulence model, say k-e RNG model? For unsteady flow,how do I jude if the flow in the channel is fully developed. Thanks!

Ray


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