Fluids

Fluids

Subsonic diffuser increases velocity and decreases pressure !?

    • simonhenn
      Subscriber

      Hello,

      I have a problem simulating an airflow through a diffuser. I use a mass flow inlet and a pressure outlet. The mass flow is 0.485 kg/s and the static outlet gauge pressure is 3600 pa. I use the Coupled Solver and comprossible flow setting.


      When I start the calculation I immediately notice that the residuals don't really decrease very much:

    • Karthik R
      Administrator
      Firstly, when I look at the residual plot, it seems like your simulation is not converged. Please make sure that your simulation converges.nWhat is your Mach number? Is the working fluid air? nHow do your inlet and outlet diameters compare?nThanks.nKarthikn
    • simonhenn
      Subscriber
      Hello, nI'm pretty sure that they would have diverged later because that's what always happens when I let it run. So I stopped the calculation to see in which direction the results are going. nThe mach number is around 0.2-0.25, the fluid is compressible air. When I solve with incompressible air it also diverges. nThe inlet area is 6*10^(-3) m^2, outlet area is 1.9*10^(-2) m^3. nActually the mass flow rate is 0.38 kg/s, I got that wrong in the question.
    • Rob
      Ansys Employee
      That should solve very quickly, so check the mesh and post some images of the flow field. n
    • simonhenn
      Subscriber
      What exactly do you mean with checking my grid? n
    • Rob
      Ansys Employee
      Is the cell quality in the acceptable range, and have you resolved the wall and flow. n
    • simonhenn
      Subscriber
      Yes, I always get told to check my mesh but which are the specific metrics I should check and in which range should they be?n
    • Rob
      Ansys Employee
      Have you read the documentation, Meshing - Global Mesh Controls - Quality Group - Mesh Metric - Skewness will give you a good starting point. Fluent User's Guide (Solution) 6.2.2 also has guidance. n
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