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  • Posted by Pratham on September 7, 2023 at 7:19 pm

    Good evening,

    Hope you are doing well. I have got an issue with a problem for multiphase tutorial. I am not able to solve the problem as the error depicting on the console bar is floating point exceeds. However, I was able to determine the coefficient of discharge for the delta p .5 and 1 bar. Delta p above 1 bar depicting same issues for all case even using optimise relaxation and advanced stabilisation.

    The input for our problem is mentioned below,

    Solution

    Pressure at Inlet: 3.5 Bar

    Operating temperature: 288.16 K

    Turbulent viscosity ratio: 5

    Algorithm used: Coupled

    Pressure: PRESTO

    Momentum: Second order up wind

    Volume Fraction: Compressive

    Modified Turbulent Viscosity: Second order up wind

    Turbulence models: Spalart – Allmaras

    Fluid density: 998.2 kg/m^3

    Outlet: Varying

    Pseudo transient: On/Off, as elementary while using pseudo transient high fluctuations are seen for problematic cases.

    Multiphase

    Homogenous Model: Volume of fluid

    Formulation: Implicit

    Interfacing modelling: Sharp

    Volume fraction cutoff: 1e-5

    Remarks, the case taken here in 2D as to formulate a structural mesh. Mesh data is given below.

    Orthogonal quality: 0.99991 (Avg.)

    Skewness: 5.9019e-003 (Avg.)

    No. of elements: 112512

    Please go through the attached images for mesh reference. Hope you will understand.

    Thanking you,

    With regards,

    Pratham Chauhan.

    Sandeep replied 7 months, 1 week ago 2 Members · 5 Replies
  • 5 Replies
  • Pratham

    Member
    September 7, 2023 at 7:23 pm

    More reference at delta 1.5 bar

  • Pratham

    Member
    September 7, 2023 at 7:24 pm

    Fluctuations countered, at 1.5 bar

  • Sandeep

    Administrator
    September 7, 2023 at 8:34 pm

    Please use k-omega SST model and Pseudo transient approach with a time scale factor of 0.1. That should help to stabilize it

  • Pratham

    Member
    September 8, 2023 at 3:27 pm

    Good evening,

    Professor,

     

    Thank you for your earlier response. I will definitely do that. But I have a doubt regarding  (Coefficient of discharge). For example, for delta p at .5 bar my mass flow rate at outlet is around 80.943439 kg/s. Whereas ideal mass flow rate is 1000 kg/s approximately.

    If I apply the given values to the formula. My  is coming around 0.08, which is wrong in my opinion. Remarks area of outlet is 0.1 m^2.

    Hope you will understand.

    Thanking you,

    With regards,

    Pratham Chauhan.

    • Sandeep

      Administrator
      September 11, 2023 at 5:45 pm

      There cannot be that much difference between your ideal mass flow rate and CFD mass flow rate. Max 50% deviation is possible which will give you a Cd around 0.5. So there is some issue in your calculations, either CFD or ideal.

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