Transient modelling in Fluent

Ganeshsswamy · November 15, 2019, 05:08

HI,

I am currently working on a huge volume evacuation. My domain mainly has a huge cylinder of 1m radius and 200mm height. inlet is closed (no flow). Outlet is opened and gradually i will reach vacuum conditions through a turbopump. i have done many simulations in the past where in there is an in and an outlet. In this case, since there is not inlet, i am not able to converge. Can someone help, please. Thank you.

MKuhn · November 26, 2019, 10:43

It should work to a certain point. Try to lower your time step. Try to soften the starting point, decreasing the pressure difference, refine the cells close to the outlet.

As the solver is based on the the Navier–Stokes equations you need a continuous mass flow, lowering the pressure, up a certain point this is not the case anymore and you have to describe your flow in a different way. I don't know if Fluent can deal with it. See Knudsen-number in the literature and maybe in the thery guide for more details. Set the pressure at your outlet not to 0, find a value where the Knudsen-number is still < 0.1 or even < 0.01.

November 15, 2019, 05:08	Transient modelling in Fluent	#1
Ganeshsswamy New Member Ganesh S Swamy Join Date: Sep 2009 Posts: 6 Rep Power: 16	HI, I am currently working on a huge volume evacuation. My domain mainly has a huge cylinder of 1m radius and 200mm height. inlet is closed (no flow). Outlet is opened and gradually i will reach vacuum conditions through a turbopump. i have done many simulations in the past where in there is an in and an outlet. In this case, since there is not inlet, i am not able to converge. Can someone help, please. Thank you.

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November 26, 2019, 10:43		#2
MKuhn Senior Member Moritz Kuhn Join Date: Apr 2010 Location: Germany, Dresden Posts: 207 Rep Power: 17	It should work to a certain point. Try to lower your time step. Try to soften the starting point, decreasing the pressure difference, refine the cells close to the outlet. As the solver is based on the the Navier–Stokes equations you need a continuous mass flow, lowering the pressure, up a certain point this is not the case anymore and you have to describe your flow in a different way. I don't know if Fluent can deal with it. See Knudsen-number in the literature and maybe in the thery guide for more details. Set the pressure at your outlet not to 0, find a value where the Knudsen-number is still < 0.1 or even < 0.01.