gas-liquid modeling in a stirred tank

tsh850227 · October 12, 2016, 04:48

Hi All,

I am modelling a gas-liquid system in a stirred tank with CFX.

Several spargers were located at the bottom of the tank, and impeller was in separated domain with a specified rotating speed. the buoyancy model was activated as density difference. turbulent models were specified as k-e for fluid at inlet with intensity of medium. The top of the tank is specified as degassing condition. My case is nearly exactly the same as the tutorial provided by ANSYS. I followed the setup in the tutorial.

However, this simulation suffered very strange errors: with steady state mode, calculation diverges and failed with a notice of overflow. I monitored the the gas exchange at the sparger and top of the tank. it seems that after several initial iterations, there would be some gas trying to flow into the domain from the top. I think this is the main reason why the calculation failed.

so anyone can advise?

thanks in advance

ashi.ismd · October 12, 2016, 14:24

Hi
You might try working with Volume of Fractions [VOF]. I would set an initial surface of the fluid, say a plane and impart a definite VOF, say 1 to it. I will then run the simulations. Overflow usually occurs when the mesh is not resolved fine enough of when the time step / CFL is usually way too high.

October 12, 2016, 04:48	gas-liquid modeling in a stirred tank	#1
tsh850227 Member Join Date: Jan 2012 Posts: 30 Rep Power: 14	Hi All, I am modelling a gas-liquid system in a stirred tank with CFX. Several spargers were located at the bottom of the tank, and impeller was in separated domain with a specified rotating speed. the buoyancy model was activated as density difference. turbulent models were specified as k-e for fluid at inlet with intensity of medium. The top of the tank is specified as degassing condition. My case is nearly exactly the same as the tutorial provided by ANSYS. I followed the setup in the tutorial. However, this simulation suffered very strange errors: with steady state mode, calculation diverges and failed with a notice of overflow. I monitored the the gas exchange at the sparger and top of the tank. it seems that after several initial iterations, there would be some gas trying to flow into the domain from the top. I think this is the main reason why the calculation failed. so anyone can advise? thanks in advance

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October 12, 2016, 14:24		#2
ashi.ismd New Member Join Date: Aug 2014 Location: Lexington Posts: 11 Rep Power: 11	Hi You might try working with Volume of Fractions [VOF]. I would set an initial surface of the fluid, say a plane and impart a definite VOF, say 1 to it. I will then run the simulations. Overflow usually occurs when the mesh is not resolved fine enough of when the time step / CFL is usually way too high.