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Turbulent Dissipation Rates - epsilon

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Old   May 16, 1999, 02:37
Default Turbulent Dissipation Rates - epsilon
  #1
Otute
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Hello;

In most CFD studies, the velocities and turbuelnt k-e are reported and or of interest. Has any one done or know of an in depth study of how well CFD codes (Fluent 4.5/5.0 in particular) predict the dissipation ot turbulent kinetic energy in 3D systems - with respect to:

1. Choice of turbulence model (k-e, RNG k-e, RSM etc ..) 2. MRF, sliding mesh, or experiemntal BCs

Thanx.

-Otute
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Old   May 16, 1999, 06:20
Default Re: Turbulent Dissipation Rates - epsilon
  #2
Sridar.D
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hello,

i haven't worked with any of cfd software. but i think this information will be of use to you.

so far our research on dissipation modelling by existing numerical methods shows a loss in prediction(this iam talking in the context of DNS and LES), i.e. the amount of dissipation obtained by these discretization technique is less than the exact dissipation at the higher k's in turbulent energy spectrum.

if you are going to model the turbulence problem, at much lower k's by any of the turbulence model, definitely you are going to lose some important information, that's where DNS and LES comes in to picture (where DNS goes right up to kolmogrov's scale and LES does up a maximum possible cut of wave number).

with the present CFD codes and turbulence models there is an underprediction of the dissipation, which one has to take care by adding explicit dissipation to compensate for the loss.

regards!

Sridar.D, M.Tech.(Aerodynamics), center for Aero CFD, IITK, INDIA.
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Old   May 16, 1999, 06:36
Default Re: Turbulent Dissipation Rates - epsilon
  #3
abdul aziz jaafar
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Dear Otute

The following paper may be give some information

So RMC, Zhang HS and Speziale CG 1991 Near-wall modelling of the dissipation rate equation AIAA Journal Vol 29, 12 pp 2069 - 2076

AAJ
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Old   May 17, 1999, 11:39
Default Re: Turbulent Dissipation Rates - epsilon
  #4
John C. Chien
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(1).In the two-equation model, the epsilon equation should be considered as the length-scale equation. It should not be considered as the real equation for the dissipation of TKE. (2). In the past, several other parameters have been used as the length-scale equation. (3). When a two-equation model is used, the only meaningful parameter for comparison is the TKE. This is because the convection of dissipation, the diffusion of dissipation, the production of dissipation, and the dissipation of dissipation are very confusing terms. It is a good idea not to attach a physical meaning to this second length-scale equation. The use of TKE in comparison should be enough.
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Old   May 20, 1999, 07:39
Default stability of combustion in gas turbines
  #5
karim
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Hello, I'm looking for some body who can give some informations in this domain.

Sincerly
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Old   May 20, 1999, 10:51
Default Re: stability of combustion in gas turbines
  #6
John C. Chien
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(1). You must read " Mathematical Models of Turbulence" by B.E Launder and D.B. Spalding, 1972, two masters in the field of turbulence modeling. (2). Search for any papers published by W. Rodi in ASME Journal of Fluid Engineering, and AIAA Journal. (3). VKI reports and lecture series. (4). Various turbulence models can also be found in Internal Journal of Heat and Mass Transfer.
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