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Notes on Turbulence Modeling

  • All turbulence models are wrong, some are useful! George E. P. Box
  • In turbulence modeling is always some empiricism and uncertainty involved
  • There is no universal turbulence model
  • Each test case is specific, scales and speeds are important
  • If not sure which turbulence model to use, choose 49 1 50 1 51 1 52 1
  • For each turbulence model the proper initial and boundary conditions have to be specified
  • Wall treatment is important
  • Wall functions may not work for 34 1 13 2 39 2
  • Generally speaking, wall functions is the approach to use if you are more interested in the mixing in the outer region, rather than the forces on the wall.
  • We never know a priori the 34 1 value.
  • 34 1 value is different for compressible and incompressible flows
  • Always use the default model constants unless you know what are you doing or you are confident that you have better values.
  • Turbulence modeling effect on results is often overestimated!
  • Turbulence effect may be higher in external aerodynamics, than in internal aerodynamics.
  • There are many cases, where the turbulence model has very small effect on results
  • Beginners should concentrate more on fluid mechanics (BTW: 80% of all errors are caused by wrong boundary conditions of pressure and velocity).
  • The results matters! Sometimes the results go against the turbulence theory.