Hi, In my arrangement I simulate pipe in which on the one side the air is blowed into (velocity inlet BS). On the other side there is a "pulsating" valve which opens and then sucks air with lower pressure than closes and repeta, etc. My arrangement is an inlet pipe for automobile before valves. Can anyone have a suggestion what BS set for this second (valve) side of a pipe.

Luk

It seems you can not do it without UDF - there are some examples in the FLUENT user guide for the definition of various BC

BR

Olek

I know that I have to use CFD but I don't know which type. As far as I know the wall BC (closed valve) means that V=0 on entire boundary. I dont know how to connect it with pressure douring the valve is opened.

Luk

Dear Sir: 1-What is the value of B.C through inlet valve static pressure K + epsilon 2- Can I drow the result by other software?

You need a pressure bc which mimics opening and closing action. A pulse profile for a time interval will need a negative pressure for that interval (sucking) and closed condition pressure at other times. The pulse will end after some time interval and repeat itself as long as you allow it. You can actually see these profiles if you monitor pressure at outlet with time and should see toothy profiles!

Hope it works for you.

Swarup.

Dear Swarup, What does it mean "closed condition pressure". For now I tryed following things: I think that inlet BC type velocity inlet is not acceptable for that because it generates backflow warning (which is not physical) if the valve is closed. So I try to give fan inlet with pressure set such that air speed in full open valve is equal to that generated by velociy inlet condition. In this case closed valve is generated by setting this value of pressure (with changed sign) in the outlet. The problem is: what to do If I set an inlet to the channel as hole in a solid (situation like in wind tunnel test of cars at given speed). Then the velocity on the front of the tunnel is set and I don't know what is pressure of the inlet of channel (because it depends on geometry of the solid and so on). What to to then to close a valve?

Closed condition pressure is the pressure you expect to have at outlet when sucking is stopped, say 0 gage pressure.

In my opinion, backflow is quite normal for this case as pressure is varying from a "sucking" one to a "pushing" one. I guess that is what should happen first in your outlet and then possibly propagate to inlet.

Mechanism for valve closure does not change.

Swarup.

I am not quite sure if I understand You well. For me, in ideal case: sucking (valve opened) - BC=pressure outlet; sucking stopped (valve closed) - BC=wall, because flow is stopped and pipe is stucked. However I am not sure If it is possible to make such a "mixed" BC as UDF?

Once again very thanks for Your interest, Luk