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Shazlan February 18, 2005 05:11

BC Problems/Confusions
Hi all,

I need to analyze a toiletbowl. The problem is in setting the boundary regions. The inlets, where the water is flushed into the bowl, is okay - at least, that's what I think. The outlet is located just after the siphon. The problem is on how to indicate the open area (where our butt is). I was thinking of using pressure BC, since it is subjected to atmospheric pressure and temperature, but pressure and outlet BC cannot co-exist. How do I 'tell' star-cd that the area, which consist of atmospheric air? or in other words, how do I go about approching this problem. I am assuming that toiletbowl is quite common that everybody knows the general geometry and concepts on how it works. Your help is highly appreciated!

Ted Crilly February 19, 2005 13:04

Re: BC Problems/Confusions
as far as i can remember

i'm sure pressure and outlet can co-exist in the same model/domain,

the outlet has to be fixed, ie. 1.5 kg/s not split (0.5) etc,

so choose a fixed outlet with the flowrate that you know and specify it, then use pressure boundary with pressure details / atmospheric etc

it should work fine, just make sure not to use split option of outlet

ted crilly

Shazlan February 21, 2005 04:35

Re: BC Problems/Confusions
Thanks for your comment.

However, the flow rate at the outlet is not fixed and not known a priori - it is hope to know the value from the analysis. How else can I incorporate the atmospheric details in my analysis? Please advice.

Ted Crilly February 22, 2005 03:52

Re: BC Problems/Confusions
hi ,

i would have thought the volume/mass of water is fixed, for example if your toilet has a 15Litre cistern, and it flushing in 15 seconds etc. This could be setup as a fixed outlet boundary @ 1 litre/second.

You other alternative i believe would be to use multiple pressure boundaries, if your flows are not fixed, you would need accurate pressures though to predict the flows correctly etc

-ted crilly

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