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PriA October 16, 2007 15:31

pump as a momentum source
Hi everybody! I'm working with a pump in a tank, the fluid is water. I want to know why analysing the results at CFX-Post, my pump generates momentum in all directions, but I just used value for y direction and zero for the others. I'm wondering it's like the software gets confused about my pump and what it means. I set two bodies, one inside of the pump and the other between the pump and the tank. It's right, isn't? What can I do to fix it? Tks so much

Chirag October 17, 2007 04:05

Re: pump as a momentum source
Hello PriA

I understand that you are trying to analyse a pump submerged in water tank.

What boundary conditions / interfaces are you using?


PriA October 19, 2007 12:34

Re: pump as a momentum source
Hi Chirag!

I'm using as boundary conditions an Inlet with no mass flow, because my tank doesn't have fluid entering, and a Wall condition (wall influence on the flow: no slip). I'm wondering if the CFX isn't understanding my pump as a pump inside of a tank. To fix it, I'm thinking of creating other surface envolving the pump; like a hole with the pump in. What do you think? Do you have any other suggestion? Tks so much!!!!

Chirag October 20, 2007 06:07

Re: pump as a momentum source
Hello PriA.

A) If there is no fluid entering tank & on the other side pump is sending fluid out of tank, then it becomes a transient problem with moving mesh. Which is quite complicated. Have a second look at it & see if it's really necessary.

B) If not, then you can go for a steady state problem. But here, do not set inlet boundary with no mass flow. Set inlet boundary with static pressure specified over it or set an opening boundary instead.

Now, are you modeling exact pump geometry? What exactly do you want to conclude out of this CFD? This will give us some more idea.

Best luck,


PriA October 23, 2007 07:53

Re: pump as a momentum source
Hi Chirag

I've modelled the pump geometry like volume. I think it's better, since it respects the direction of my momentum source (what it's not happening). I want to compare the same situation on CFX with FLUENT. I have the results on FLUENT, but I don't get it on CFX.

Tks for your help!

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