Hello, everyone,

My research model has 2 inlet and 2 exits. I gave the velocity inlet BC to the 2 inlets, which correspond to two kinds flow rate waveforms (this is an unsteady problem). Then I need to define the two outlets as fully developed with certain flow rate waveform. It seems that outflow BC can keep the flow at exits fully developed. However how to give the flow rate waveform (transient flow rate) at exits at the same time? The outflow BC seems only support the constant flow rate distribution.

Would you please to give me some advices on it?

Thank you for your time! Regards, Junmei

If you mean that you want at outlets time-dependent flow rate, for example mass flow rate, it is very easy.You create a simple udf file (c++) and you adapt it in the BC panel. you will use DEFINE_PROFILE and you will write there the function of time. Look in the documentation there may be exist and a special DEFINE macro for mass flow rate. I have done something like that with transient velocity inlet. If you have problem with that contact free.

Hi, STK, Thanks for your time and kindly suggestions! You are right. I exactly want to set outlets with time-dependent flow rate and fully developed flow there at the same time. However the outflow BC cannot support UDF. In the panel, we only can define the outflow mass weight (a constent value). In addition, if I define the outlet as pressure outlet, it also cannot satisfy the time-dependent flow rate because "target flow rate" only support constant value.

Therefore would you please give me further suggestions?

Thanks a lot in advance! Regards, Junmei

It is my pleasure to help you. In the panel you see a blank space near label:time-dependent flow rate because you haven't interpret or compile a udf. I can't believe that udf are not supported in outflows. Please tell me exactly the outflow b.c in fluent (to see if udf is supported) and i will send you a time dependent function. Afterwards you can change it to your problem settings. regards!

Dear STK, Thanks for your kindly reply very much! In fact, I have compiled the UDF for the inlet-velocity, which is a time-dependent function. After I compiling it, I can find it in the panel of ¡°velocity-inlet¡±. However the UDF cannot be found in the ¡°outflow¡± panel after I compiled it. Do you meet the same phenomena? And would you please to give me further suggestions? Thanks a lot! I am looking forward to hearing from you! Regards, Junmei

I checked it out you have to change b.c. try pressure outlet

Dear STK, Thanks for your kindly and prompt reply very much! Yes, with the pressure outlet, the flow can be fully developed there. However it is difficult to keep the flow rate waveform because Fluent 6.1 only provides the constant ¡°target flow rate¡±. So it seems difficult to set the BC as fully developed with prescribed waveform. I am looking forward for your further suggestions! Thanks a lot! Regards Junmei

TELL ME THE FUNCTION TIME OF PRESSURE OUTLET TO SUCCEED WAVEFORM FOR YOUR RATE

Dear STK, Thanks for your kindly reply! Actually the problem is that I do not know the pressure waveform at the outlet, I only know the flow rate waveform. So I want to set the outlets as fully developed with certain flow waveform¡*. Sorry for troubling you a lot! If convenient, would you please give me some suggestions? Thanks a lot! Regards, Junmei

WHICH IS YOUR CERTAIN FLOW WAVEFORM?

Dear STK, Thanks for your kindly replay always! The flow waveform is like the aorta waveform. If convenient, would you please to tell me your email address? Then I can send you the flow rate waveform. Thanks a lot! Regards, Junmei

stkarabelas@hotmail.com