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  3. I am running a converging nozzle simulation in Fluent and I have used DEFINE_PROPERTY to define my own ideal gas law for density. When I run the simulation, the flow through the nozzle is isothermal. How can this be? When the flow accelerates, temperature should fall.

I am running a converging nozzle simulation in Fluent and I have used DEFINE_PROPERTY to define my own ideal gas law for density. When I run the simulation, the flow through the nozzle is isothermal. How can this be? When the flow accelerates, temperature should fall.

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    • April 5, 2023 at 2:32 pm
      FAQFAQ
      Participant

      DEFINE_PROPERTY can be only be used to define density (as a function of temperature) for gases. Implementing a state law with DEFINE_PROPERTY drops the compressibility terms from the energy equation and will result in isothermal flow through the nozzle. To implement the full state equation, the example in the documentation entitled “Ideal Gas UDRGM Code Listing” (in the Fluent Customization Manual) should be used. This fulfills the requirement for thermodynamically consistent definitions for density and Cp. Thermodynamically consistent relationships for Density and Cp are ones that obey the state equation for Enthalpy. For a full explanation, please see the description in the CFX Theory Guide> Basic Solver Capability > Governing Equations > Equations of State > General Equation of State

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