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Old   May 17, 2014, 08:22
Default Flovent instability
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Rasmus Vilsbøll
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Hi guys.

I am running some cases on diffuse ceiling ventilation for my master's thesis. I run into some issues when changing flow rate:

When changing from a relatively low flow rate (0.05 m3/s) to a higher (0.25 m3/s), having done a grid independency study, all variables suddenly become very unstable, and convergence will never occur. My monitor points are also very unstable.

Maybe the problem is related to the following issue:

I have a fixed flow on my inlet. In the room I have heat sources simulating the presence of people. How should I define my outlet? I have the following options:
- Fixed flow outlet (if there is a density change, which there is, I don't conserve mass)
- Fan (I can define a stagnation pressure, which I understand as the pressure on the fan at which the fan stops?) At low flow rate this type of outlet is the only ensuring mass balance.
- Perforated plate

Currently I have fans installed.

I'm a little new to CFD so my apologies if the answers to my questions are obvious

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