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-   -   Gravity influence of flow :Urgent (http://www.cfd-online.com/Forums/fluent/31929-gravity-influence-flow-urgent.html)

 Suresh Balasubramanian August 3, 2003 12:41

Gravity influence of flow :Urgent

Hi,

I have laminar flow through a pipe intersection and i want to see the influence of gravity?

I turned on the gravity option and also set the operating density to zero. When I solve using velocity at the inlets & pressure at outlets I see that the residuals don't go below 1e-3. They keep varying at a residual value of greater than 1e-3 I have a terahedral meshed 3-D domain.

When I stop the iterations I see a Hydrostatic pressure distribution which is correct.

I also see that some of the velocity vectors point out of the domain. (Seems as if inclusion of gravity makes the vectors point out of the domain).

If anyone of you have seen a similar problem I would be greatful if you can help me. It's urgent.

Thank you very much,

Suresh

 Mcgregor August 4, 2003 05:11

Re: Gravity influence of flow :Urgent

Hi Suresh

If you identify which residulual is not going below 1x10 -3 then you can go into the solve/control/solution panel and decrease the relaxation factor relating to that variable (ie continuity). This should solve this problem as the solution will then converge

Mc

 ap August 4, 2003 08:28

Re: Gravity influence of flow :Urgent

Try reducing momentum under-relaxation factors.

If you're using an high order discretization scheme, try to obtain a first solution using the first order scheme, then switch to the higher order one.

Hi

ap

 Evan Rosenbaum August 6, 2003 11:06

Re: Gravity influence of flow :Urgent

While I've only used gravity when evaluating buoyancy problems, I'm not sure you should specify a zero operating density. The gravitational force on anything without mass is zero.

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