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Old   March 17, 2008, 08:29
Default outdoor HVAC simulation
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Hello I am trying to simulate a large scale problem and i am facing some boundary conditions related problem.

The problem involves an architectural project made up of 7 2 story buildings, distributed around a central plaza. The plaza is being cooled with air that enters at ground level.

the model i have created includes all the buildings, and the air outlet area. the bounding box is extended 60m outside all structures. (300m x 300m x 60m)

My problem involves the modeling of the surrounding boundary conditions, i've used opening BC with every single possible option, and i've tried using inlet conditions with zero total pressure. Every way i try to do it, i get very high speed flows (300m/s)at the BCs for the surrounding areas.

The ambient temp is 40C and the cool area is at 20C, so i have to use the buoyancy model, which i suspect is causing the problems.

i have tried using an expression for the pressure gradient on the vertical BC but to no avail. the only condtion that produces physical results is using Free slip walls for the surrounding areas with the excpetion of the sky bc, which i use an opening for.

pls Help

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Old   March 18, 2008, 09:00
Default Re: outdoor HVAC simulation
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Ok best thing to do is break down the problem as your model is way too complicated to sort out BC's. Just setup an empty box, and test your BC's with and without bouyancy. Once you are happy, then try and apply what you have found to the complex model. That should improve your turn around times. Are you usign the full buoyancy model or the bousinesq (cant spell - sorry).

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Old   March 18, 2008, 09:07
Default Re: outdoor HVAC simulation
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I've tried both models earlier when the problem started occuring. But i've stuck with the full model. I'm using my ref density 1.15 kg/m3 i'm currently exeperimenting with diff boundary conditions
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