CFD Online Discussion Forums

CFD Online Discussion Forums (
-   CFX (
-   -   re: Massflow reset in CFX 10 (

Wooster March 12, 2007 14:12

re: Massflow reset in CFX 10

I'm inducing flow in a model via the massflow option. The massflow is 0.18 lbm/sec. This is inputted into the inlet and outlet (mass conservation). When the model is ready, it shows a proper distribution of massflow (equal throughout) but the inlet and outlet values are between 1E-4 and 3E-3 lbm/sec. I'm stuck trying to figure out how on earth 0.18 went to 0.001. Any suggestions? I feel as though there is some check box lurking in the background I should've checked. For troubleshooting, the inlet was setup with the massflow, the outlet condition was setup with a massflow and the "Scale Mass Flows". Thanks!


Joe March 12, 2007 15:14

Re: re: Massflow reset in CFX 10
Setting mass flow on both the inlet and outlet BCs is going to lead to issues.

Set a mass flow at the inlet and let the outlet calculate itself with an outlet-type BC.

Wooster March 12, 2007 18:06

Re: re: Massflow reset in CFX 10
What would you suggest the outlet condition to be? I would know most if not all the inlet conditions, but the outlet is an unknown. By forcing the massflow at the outlet I was thinking I'd have something to plug in. While its not a big thing with most of my models, there are a few where I need to setup a design and examine the differential pressure CFX calculates (outlet pressure/flow unknown).

klarke March 12, 2007 21:12

Re: re: Massflow reset in CFX 10
your question is not closed at all for such boundary conditon.(U,v,w,P),where is the p reference?

HekLeR March 14, 2007 22:51

Re: re: Massflow reset in CFX 10
ok, masflow outlet and total pressure inlet?? works fine if the flow is not choked.

Wooster March 16, 2007 21:08

Re: re: Massflow reset in CFX 10
Ok, I'm using for a particular model the inlet massflow (which is now working) and an outlet pressure condition of zero psi (good call Joe). This will work for this model. If there is a reference pressure (say 300 psi) how will the zero pressure outlet effect it? I have a model where I know some basic flow into the part, the reference pressure, but I know nothing of the outlet. In fact that is what I'm trying to figure out is whether the set of designs will improve dp and cooling of the device. Klarke, I don't know quite what you are asking. Now the model I'm working on has empirical data and so I'm busy benchmarking CFX against it. As for geometry, its a simple water jet blasting a hot plate. I have some volumetric heating questions but I'll save 'em for another thread. Thanks!

All times are GMT -4. The time now is 08:59.