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Saikat February 9, 2005 14:14

Boundary conditions in CFX-Pre
This condition is to simulate room air flow, when an airlock is maintained between two rooms. Let us say we have two rooms one with higher pressure and one with lower pressure. The one with lower pressure has an extract, and one with higher one has inlet (obvious but still I prefer to describe it fully).

The two rooms are joined by a small window (filter) which lets some airflow through it so that the pressure differential is maintained for the two rooms. Also there is a door connecting the two rooms which is closed at time t=0. Now when the door is closed all the air has to pass through this filter from the HP room to the LP room. How to define the boundary conditions for this filter? I defined both the rooms to be different domains and then the filter acts as the third domain, joining the two. But the boundary conditions for two sides of the filter (each side connecting to a room respectively) I cannot clearly define yet. I know that, it has to take care that the pressure differential remains maintained, as also one has to consider when the door will eventually open in later stages of calculation, the air flow through the filter decreases since then the door opened takes care of the airflow required. But then the pressure differential is goofed up as well. But as soon as the door is closed again, the filter action would bring back the normal condition in some time.

I thought that one may be tempted to say that forget all different domains, just make one domain and let the program decide how it wants to flow. But then I want to have a calculation which gives me the pressure differential calculated in transient flow across this filter. So want time dependent values of pressure across it, when the door is opened and closed again. Is there someway in which I can tell CFX I want delP across the filter to be ## value, when the door is closed, but then when the door is opened how to make the filter realise this and reduce airflow through it??

Help would be appreciated. Thanks

Glenn Horrocks February 9, 2005 17:37

Re: Boundary conditions in CFX-Pre

For the filter have a look in the documentation for momentum sources and sinks. There are a number of different mechanisms available for modelling flow resistance.

Glenn Horrocks

Saikat February 10, 2005 08:22

Re: Boundary conditions in CFX-Pre
Glenn, Thanks a lot. I also came to the same solution looking through the tutorials etc, teaches me, I have to research more before putting up a problem here. Regards Saikat

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