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-   -   help! Mass flow outlet again (http://www.cfd-online.com/Forums/fluent/31252-help-mass-flow-outlet-again.html)

Z. T. April 9, 2003 10:11

help! Mass flow outlet again
 
Hello,

In my project, mass-flow-rate in outlet is needed. I have ever tried using the scheme file someone posted before to do that. However, a error in Fluent6 is shown as follows:

Loading "E:\mesh ind\mesh4\mfo.scm"

Error: eval: unbound variable Error Object: )

what does give rise to this error? The scheme file is based on Fluent/UNS. Could anyone help me get one for Fluent5/6?

Thanks!

zheng

HVN April 9, 2003 10:17

Re: help! Mass flow outlet again
 
Hello

Why don't you use the surface monitor for that in fluent 6 ?

HV

HVN April 9, 2003 10:39

Re: help! Mass flow outlet again
 
or report with surface integral

Z. T. April 9, 2003 10:54

Re: help! Mass flow outlet again
 
Hi HVN

Thank you for your suggestion. In my case, only pressure in inlet and mass flow rate in outlet is known. so I need special boundary condition.

please see the message as follows:

http://www.cfd-online.com/Forum/flue....cgi?read=1224


Ahmed April 9, 2003 11:33

Re: help! Mass flow outlet again
 
There is no mass flow out boundary condition..In the same time out flow boundary condition cannot be used with compressible flow..therefore I suggest to use pressure outlet BC then you can monitor the mass flow at the outlet then ajust the pressure to get the required mass flow.

Z.T. April 9, 2003 12:24

Re: help! Mass flow outlet again
 
Hello Ahamed:

Thank you for your advice. I think it is good idea. I am thinking, can I prescribe velocity magnitude in outlet by using velocity-inlet(set flow direction as -1)? Is this a way to solve the problem?

Thanks!

zheng

Hendawi Mohamed April 10, 2003 04:42

Re: help! Mass flow outlet again
 
Hello fluently,

I think that in your case, the better solution is to specify a target-mass-flow-rate with pressure-outlet as boundary condition (Cf. /help/html/ug/node198.htm).

for more information you can refer to these messages posted in response to Thierry who is almost in the same case as yours.

http://www.cfd-online.com/Forum/fluent.cgi?read=12288

cordially

Mohamed

P.S.: With Fluent 6 this option is Ok but I don't know if there is some restriction in Fluent 5,

Thierry April 10, 2003 05:18

Re: help! Mass flow outlet again
 
Hello !

Mohamed is right, with FLUENT 6.1.18 you can specify a target-mass-flow-rate with pressure-outlet BC...it's a little bit slow but it seems working.

Thierry.

Z. T. April 10, 2003 05:35

Re: help! Mass flow outlet again
 
Hello Mohamed and Thierry:

Thank you for your help! I am tring to do that.

By the way, I want to ask a question: My project is 2D. In this case, is the depth per unit length(1m) in Fluent by default? I need this value to calculate mass flow rate corresponding to 2D geometry.

Thanks!

Ahmed April 10, 2003 08:51

Re: help! Mass flow outlet again
 
(1)You can specify the profile..

(2)Sure It is 1m, Actually it is convention everywhere..

Volker Pawlik April 10, 2003 08:55

Re: help! Mass flow outlet again
 
it is always 1 m independet from what you set in reference values panel!!!


Volker Pawlik April 10, 2003 08:59

Re: help! Mass flow outlet again
 
I must correct my answer to be better understandable:

The massflow you set must be the massflow for a depth of 1 m, independent from what you set as reference depth. Fluent calculates the corresponding massflow for your reference depth!!


Z.T. April 10, 2003 12:27

Re: help! Mass flow outlet again
 
Thanks to all!


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