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-   -   How to specify mass flux for an outlet? (https://www.cfd-online.com/Forums/main/5043-how-specify-mass-flux-outlet.html)

 Bigarella August 14, 2002 16:23

How to specify mass flux for an outlet?

Hi,

How do I implement a boundary condition for an outlet where I have a specified mass flux? I think it should be done by means of a static pressure correction, but I don't know how to do it.

My code is a 3-D, cell-centred, face-based FVM and BC's are implemented with ghost volumes.

Thanx!

 Martin Nilsson August 14, 2002 17:10

Re: How to specify mass flux for an outlet?

Generally, stability can become an issue if defining the mass flow for an outlet. Static pressure is the "best" bc for a subsonic outlet. There are ways around it, as Fluent etc have implemented in their codes, but it is not entirely stable there either. So, my advice is that you use Ps on your outlet.

 Jannis Dotsikas August 15, 2002 08:52

Re: How to specify mass flux for an outlet?

Hallo,

what you can do is to calculate the whole mass flux at your inflow boundaries. What is coming in, should leave your computational domain. After some iterations a small amount of gas should leave your computational domain. You summarize it and you find the mass flux leaving your computational domain. You build the ratio (Mass flux IN)/(Mass flux OUT) and you multiply the mass fluy of every cell with this ratio. As every iteration is only a better approximation of your solution, it doesn't bother you, that you might have introduced a mistake. After some iterations you should stop correcting your fluxes and your code has to find the proper solution. You have only accelerated your solution.

best regards

Jannis

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