Fluids

Fluids

CFX Phase-Change simulation with RGP-Data of water

    • Seryoga
      Subscriber

      Hello dear Ansys Community,


      I'm trying to setup a steady-state simulation with a phase change/vaporization of water. Therefore I'm using a RGP file which contains all the information for the liquid and the vapour phase. The setup is very basic:



      • Heated straight pipe with a mass flow condition at the inlet and a static pressure condition at the outlet.

      • I created two independent new Materials; waterLIQ (Thermodynamic State: liquid) & waterVAP (Thermodynamic State: gas) using my RGP file.

      • For the final Material I used the Homogeneous Binary Mixture adding the two materials together and linked the SATTable of the RGP file with it.

      • Heat Transfer: Total Energy inc. Viscous Work Term

      • Turbulence: SST


      Slover Control:



      • High Resolution

      • Turbulence Numerics: First Order

      • Timescale Control: Auto

      • Timescale Factor: 0.001


      In theory I want the water to flow in as a liquid and heat up to form a gaseous phase. Therefore I set up the waterLIQ as Equilibrium Fraction (1.0 at the Inlet) and the water VAP as Equilibrium Constraint. - Hope it is the right setting so far.


      Unfortunately I'm struggeling with the simulation. As soon as the Temperature reaches the boiling Point of water I get the following message:



      The Total Pressue turns negative and forces other variables to clip. The simulation is also not converging. I tried to simulate only an one-phase flow using either only waterLIQ or waterVAP. Everything went fine and converged delivering the right results.


      I hope somebody already did a phase-change simulation with RGP data and could help me somehow or at least give me some advice for the general setup (or point out some errors). Thank you!


      Sergjo

    • Surya Deb
      Ansys Employee

      Hello Sergio,


      You can try to change the Newton iteration under-relaxation by right clicking on the Homogeneous Binary Mixture and then modifying the CCL:


      ...


      ...


      ...


      Material Group = Wet Steam, IAPWS IF97


       Option = Homogeneous Binary Mixture


       Newton Pressure Criterion = 1[Pa]


       Newton Pressure Iteration Limit = 150


       Newton Pressure Under Relaxation = 1


      ...


      ...


      The above is an example for Wet Steam. 


      After the change, you can click Process to process the CCL.


      CFX-Pre will produce an error if they are inserted in the wrong place. Available options for other mixtures (e.g. Hydrocarbon Fuel and Reaction Mixture) can be found in the “RULES” file located at C:Program FilesANSYS Incv1xxCFXetcRULES where “v1xx” is your ANSYS/CFX installation version.


       


      Hope this helps.


       


       


       

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