HEM with Fluent: Use NIST Real Gas Model in 2-phase region

c_023 · December 2, 2019, 08:08

Hi everyone,

I am trying to model a two-phase flow with the Homogeneous Equilibrium Model (HEM), i.e. modeling the flow as 1-phase Problem and formulating an enthalpy-based Energy equation by the means of a UDS. Then, the Enthalpy and Pressure define the thermodynamic state of the fluid and I want to obtain all material properties (Density, cp, viscosity, etc.) from the NIST Real Gas Model. Unfortunately, Fluent Needs the fluid to remain either subcooled or superheated to use the NIST real gas model, and cannot perform calculations in the 2-phase Region.
I read on the Ansys Student Forum, that some "expert commands" exist to override these Default Settings and use the NIST Real Gas Model in the 2-phase Region anyways. Does anyone know how to do this, exactly?

I would really appreciate the help, as otherwise this would require writing a full UDRGM containing the same Information as the NIST RGM.

Thanks in Advance!

duskdawn · December 12, 2019, 22:25

Hello,
I am also trying to model a two-phase flow using a barotropic equation of state. Due to the temperature-independent properties, can i use the same properties (specific_heat, enthalpy and so on) according to UDRGM example in ANSYS help documentation? Therefore, I just change the material properties (density, speed of sound and viscosity).
Is this right?
Kind regards.

karlag · April 13, 2022, 06:26

Hi, did you solve this? I'm trying to do the same!

December 2, 2019, 08:08	HEM with Fluent: Use NIST Real Gas Model in 2-phase region	#1
c_023 New Member Join Date: Dec 2019 Posts: 19 Rep Power: 6	Hi everyone, I am trying to model a two-phase flow with the Homogeneous Equilibrium Model (HEM), i.e. modeling the flow as 1-phase Problem and formulating an enthalpy-based Energy equation by the means of a UDS. Then, the Enthalpy and Pressure define the thermodynamic state of the fluid and I want to obtain all material properties (Density, cp, viscosity, etc.) from the NIST Real Gas Model. Unfortunately, Fluent Needs the fluid to remain either subcooled or superheated to use the NIST real gas model, and cannot perform calculations in the 2-phase Region. I read on the Ansys Student Forum, that some "expert commands" exist to override these Default Settings and use the NIST Real Gas Model in the 2-phase Region anyways. Does anyone know how to do this, exactly? I would really appreciate the help, as otherwise this would require writing a full UDRGM containing the same Information as the NIST RGM. Thanks in Advance!

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December 12, 2019, 22:25		#2
duskdawn New Member 管伟 Join Date: Apr 2019 Posts: 1 Rep Power: 0	Hello, I am also trying to model a two-phase flow using a barotropic equation of state. Due to the temperature-independent properties, can i use the same properties (specific_heat, enthalpy and so on) according to UDRGM example in ANSYS help documentation? Therefore, I just change the material properties (density, speed of sound and viscosity). Is this right? Kind regards.

April 13, 2022, 06:26		#3
karlag New Member Karla Jacinto Join Date: Oct 2020 Posts: 5 Rep Power: 5	Hi, did you solve this? I'm trying to do the same!