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Fluids

Fluids

Topics related to Fluent, CFX, Turbogrid and more.
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  3. Viscosity compressibility

Viscosity compressibility

    • April 18, 2024 at 4:50 am
      Zwernjayden
      Subscriber

      If I am doing a rocket nozzle flow using k-epsilon, realizable, should I be using the compresibility effects option? Not using it made the residuals oscillate and resulted in the first image. Turning it on resulted in the 2nd image. In both cases the flow looked bit different than I expected.

       

    • April 18, 2024 at 9:28 am
      Essence
      Ansys Employee

      Hello,

      What is the Mach number?

    • April 18, 2024 at 4:57 pm
      Zwernjayden
      Subscriber

      Around Mach 8 at the nozzle exit

    • April 18, 2024 at 5:06 pm
      Essence
      Ansys Employee

      Thanks for the response. What's the Mach number at inlet and at throat?

    • April 18, 2024 at 5:16 pm
      Zwernjayden
      Subscriber

      Inlet Mach should be basically zero and Mach 1 at the throat. Those are values from NASA CEA

    • April 18, 2024 at 5:29 pm
      Essence
      Ansys Employee

      Ok. Please use compressibility effects. Note:  The compressibility effects have been calibrated for a very limited number of free shear flow experiments, and it is not recommended for general use. It is disabled by default. For more information please refer the Ansys guide link (section 14.2.1.10): https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v241/en/flu_ug/flu_ug_sec_turb_choosing.html

    • April 18, 2024 at 5:40 pm
      Zwernjayden
      Subscriber

      Ok so I should turn it on? The other part of your message says it's calibrated for very limited cases. Does that mean my situation falls into that category?

    • April 19, 2024 at 6:53 am
      Essence
      Ansys Employee

      Yes, please turn it ON. Because second image looks more practical. Do you have some experimental results to validate with?

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