Hi

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

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.

-CycLone

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

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

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

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.

May be you could also see whether this thread is useful: http://www.composite-agency.com/materials-forum3.htm Regards, Ankahr

please send to me calculation of cyclone and software of this thanks