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Ahmed June 2, 2008 15:53

mass flow rate calculation

I am running a compressible LES case in a plane channel. I wanna use cyclic BC, and for that I have to specify mass flow rate to drive the flow. How do I calculate my mass flow rate. Thank you

CycLone June 3, 2008 09:24

Re: mass flow rate calculation
I don't know, how do you calculate your mass flow rate?

In other words, do you know how your mass flow rate is to vary in time? Do you have a function or table of values. If you do, you have your answer.


Ahmed June 3, 2008 11:15

Re: mass flow rate calculation
No, I do not know how my mass flow rate is gone vary with time. But what is function calculator for in CFX-Post? Can I not run unsteady case (with normal inlet and outlet) first and obtain my mass flow rate at the outlet boundary. Then I can use that to run my case with periodic BC or is there something wrong? Thank you Cyclone

Ahmed June 4, 2008 11:09

Re: mass flow rate calculation
I mean use net mass flow rate between inlet and outlet. As I am sure you would know flow rate @ inlet is not same as flow rate @ outlet for unsteady compressible case. Thanks

andy2O June 4, 2008 12:27

Re: mass flow rate calculation
1) If you know what inlet velocity you want, then the idea you mentioned in your previous reply will probably work...

2) Or you could try something simpler and compute the mass flow using estimates like: (mass flow) = (inlet velocity)*(inlet area)*(inlet density). This might work very well or very badly, depending on the details of the problem. Simple 1-dimensional analytical calculations can sometimes help too.

3) The appropriate method to use depends on the details of your simulation. *You* have to decide what results are needed for your study, and then apply the appropriate mass flow rates in CFD to get these results! We can't tell you what to do, because we don't know what your study is trying to achieve, or what conditions you are trying to model!!

Perhaps just try a few ideas and see what you get?!

Good luck, Andy

Ahmed June 4, 2008 13:16

Re: mass flow rate calculation
Hi Andy

1) Yes, I do know my inlet velocity and this idea made sense to me because for compressible unsteady flow, mass flow rate is not gone be same at the inlet and outlet boundaries. In other words mass IN is not equal to mass OUT.

3) I think I will have a chat with my supervisor and ask him which method will be appropriate for my case.

Thank you for your reply.

Ankahr June 13, 2008 08:13

Re: mass flow rate calculation
May be you could also see whether this thread is useful: Regards, Ankahr

zeinab June 20, 2008 05:55

Re: mass flow rate calculation
please send to me calculation of cyclone and software of this thanks

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