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-   -   fan driven flow, Fan BC validation (getting lost) (https://www.cfd-online.com/Forums/openfoam-solving/120452-fan-driven-flow-fan-bc-validation-getting-lost.html)

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.


Thanks for interest and comments
Peter


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