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 soonic July 7, 2013 19:16

fan driven flow, Fan BC validation (getting lost)

Hello,

I would like to use a fan in my simulation. There is a TJunction tutorial for pimpleFoam. I simplified it a little more as a straight duct with fan in the middle. I set the pressure BCs to zero to get the flow through the pipe which is driven by the fan not by the pressure difference on BCs. Finally I get no flow throught the pipe.
I tried few simple cases on straight duct with no luck to get flow driven by a fan. I wish to have the flow based on pressure drop of the ducting-network, which will set the velocity of the flow based on fan characteristics. That is how I imagine the fan should work in real and computationaly too.

There are few questions I have got.

a) How the fan BC works ? Since I am not qualified enough to read source code, I found only a thread there on the forum where is a description, but I cannot get wanted results based on fan characteristics described in a f parameter for pressure jump and velocity as pj=f1+f2*Un.

b) Which of pressures p or p_rgh I should set as fan boundary type to get correct results in case i would like to solve heat transfer with buoyantSimpleFoam? Is the pressure jump relative in units in that case ?

c) I have read about fanPressure BC, but I cannot get correct results also in my testing cases.

d) Is the calculation sensitive to initial conditions ? As I will imagine how could the pressure change through the calculation since the velocity and pressure are tied in cyclic BC through the fan characteristics.

Could anyone post me a case where the fan works as demanded ? The best would be the fan datasheet or any analytical assumption on flow rate and pressure drop which was counted in, with the setting of the simulation.