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Dan June 30, 2008 15:00

Fabric Duct Modeling
I'm trying to model a fabric ventilation duct that supplies air to a room through a porous fabric.

I have two scenarios I'm trying to represent: 1) modeling the flow inside of the duct with a vent outlet to represent the fabric strip (outlet).

2) The same arrangement as in 1), but now the dcut is discharging to ambient air, and the fabric strip is represented by a porous jump. (The computational domain in this case is the entire room that is being supplied by the duct.

In practice, the pressure is supposed build up in the duct and then flow through the fabric giving an exit flow that is normal to the fabric surface and relatively uniform down the length of the duct. What I'm seeing in the simulation is a fast escape of air from the start of the duct that decreases along the length of the duct.

I've looked at loss coefficients that increase until the solution diverges, but I'm not getting the duct to pressurize properly. I'm using a polynomial dp = k 1/2 rho v**2, and I have no real data to compare this to,so I'm using estimates from perforated plates assuming a thickness of 5 mil.

Is there another way to characterize the loss through the fabric, and is there a way to force it to be normal to the outlet surface?

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