K-omega SST Steady state or Transient

    • Abdallah1996

      Hello everyone,

      I'm performing an external flow simulation of an Ahmed body with underbody diffuser using the k-omga SST in ANSYS Fluent 18.1, i have ran many simulations using steady state solver, with the mesh refined as much as possibile considering the cells limit of 512k, and the residuals never went below 1e-3, and while monitoring values of interest (Cl and Cd) the values were not sensible.

      I have tried switching to transient, and the simulation showed indications of more acceptable results. I have some questions about this case:

      1- Is transient solver appropriate for such case?, if yes how do i determine the time step size?

      2- For the max iterations/time step, should i choose a number that ensures that covergence occurs at each time step?

      3- when should i switch from steady state to transient?

      4- as the solution converges every time step, when should i stop the calculation? is it when i get steady values for the Cd and Cl, or when the residuals converges each 1 iterations?

      Appreciate your help.

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