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non-physical turbulence viscosity in coaxial free-jet simulation with species

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Old   July 24, 2010, 15:28
Question k-epsilon problem: non-physical turbulent viscosity in coaxial free-jet simulation
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Felipe B. Ch.
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In this figure, turbulent viscosity measured on the centerline is shown in red, the affected axial velocity measured on the centerline is shown in green, and the experimental data which we seek to match is shown in orange. These curves are overlaid on top of the domain which is shown in blue.




Why would k-epsilon produce the large amount of turbulent viscosity starting at about 40% of the length of the domain?

Concentrically aligned free-jets simulated to be compared with experimental data.

Grid dependency in the direction of flow has been eliminated.

Further simulation details:
  1. Fluent
  2. 2D Axisymmetric
  3. Incompressible
  4. K-epsilon
  5. Species Transport model Hydrogen-Air
  6. Concentric velocity-inlets: inner: Hydrogen, turbulence intensity 4%
  7. Concentric velocity-inlets: outer: Air, turbulence intensity of 3%
  8. Pressure inlet: Air, 1 atm
  9. Pressure outlet: 1 atm
Very grateful for any advice or suggestions on how to remove/remedy this non-physical turbulent viscosity.

Last edited by Felipeb; July 26, 2010 at 03:20. Reason: Clarity
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Old   July 25, 2010, 08:39
Default Domain Graphic
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W.N. Anderson
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Last edited by Will Anderson; July 26, 2010 at 03:24.
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Old   July 25, 2010, 09:10
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Last edited by Will Anderson; July 26, 2010 at 03:24.
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Old   August 2, 2010, 09:27
Red face problem solved
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Felipe B. Ch.
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After taking a good view of the results obtained with the simulation, it was clear for us that this behavior was actually a physical behavior, that change is a common change because of the jet instabilities.
Taken that in account we start reviewing the rest of the simulation data and experimental data.
And the end we found that there was a difference between the experimental data normalization and the simulated data normalization.

Thanks for the ones who at least read our problem

my advise: check, double check, re-double check your data

Felipe
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