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Old   July 8, 2001, 05:40
Default One-/Two--equ--turbulence-model
  #1
Matthias
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Dear all,

I am trying to implement the k-eps-model (Lam-Bremhorst) into my 2D - FD - code. (it is a basic code, not very sophisticated, but everybody starts with small steps !!). My Question is: Knows somebody an One-equ-model, where I can at first test the k-equ. before I implement the eps-equ. The geometry I am using is a canal flow and the backwardfacing step. Further questions concerning the k-eqs-equ (Lam-Bremhorst-model):

- do I have to use the wall-damping function only in the near of the wall or also at the inlet or outlet. - I am using noslip conditions at the wall, should I implement other bcd at the wall, eg. for consideration of the log-law layer.

Thaks for the help

Matthias
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Old   July 8, 2001, 12:24
Default Re: One-/Two--equ--turbulence-model
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John C. Chien
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(1). My suggestion is: try the fully-developed channel flow case first, which is just 1-D problem. In this case you are not going to have inlet or exit. Just the wall point and the centerline point. (2). In the fully-developed channel flow case, you can also try out two turbulence models: one is the high Reynolds number model and the other is the Low Reynolds number model. (3). These two models require different sets of equations and boundary conditions. For the high Reynolds number turbulence model, normally some kind of wall function treatment is required, and you have to be very careful in the implementation of the method because most published methods did not handle it correctly.
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Old   July 8, 2001, 15:15
Default Re: One-/Two--equ--turbulence-model
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Dean
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Matthias,

There is a simple trick for implementing a one-equation model for the kind of testing you want to do. Note that the k-eps model assumes the turbulent length scale may be estimated by L = D k^1.5 / eps, where D is a constant usually assumed to be unity. All you need to do is implement the k equation, use D/L as an input number to the calculation, and use this relation to compute eps instead of getting it from the eps transport equation.
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Old   July 9, 2001, 03:05
Default Re: One-/Two--equ--turbulence-model
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Matthias
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Dear John,

thanks for the suggestion but I have already an 2D code, so I think it is to much effort to first try the implementation for the 1D case. For my problem I am mainly interested in low-Re-flow (Re <=50000). As I deduce from you post - there I don 't need an special wall treatment (wall fct.).

Matthias
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Old   July 9, 2001, 03:07
Default Re: One-/Two--equ--turbulence-model
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Matthias
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Dear Dean,

I have done this test (found in Lecture notes on turbulence, Launder, 1972 ?) but I thougth there is a more sofisticated model for my low-Re-problem.

thanks again

Matthias
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Old   July 9, 2001, 03:22
Default Re: One-/Two--equ--turbulence-model
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John C. Chien
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(1). You can easily run 1-D problem using a 2-D code, if you update inlet and exit solutions by using the computed interior station. (that is, you can use 3 rows in the axial direction) (2). No, you don't need to use the wall function treatment, and a low Reynolds number model is required.
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Old   July 11, 2001, 03:39
Default Re: One-/Two--equ--turbulence-model
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John C. Chien
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(1). I think, in 80's Dr. W. Rodi had published a review article in AIAA Journal about various low Reynolds number two-equation turbulence models. I think, the model you mentioned is an old and better one. (2). Since then, there has been a lot of development and new related models published, with some from Japan. (3). There was also a near wall turbulence modeling conference held at Arizona State University in 90's (?) (4). So, if you do some paper search, you should be able to find many different new models, hopefully with improved results.
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Old   July 11, 2001, 10:41
Default Re: One-/Two--equ--turbulence-model
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sylvain
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Older one, but models presented here are still in use in Fluent and co :

Turbulence Model for Near-Wall and Low Reynolds number Flows : A Review

Patel, Rodi and Scheuerer

AIAA Journal vol 23 no 9 - 1984

and in 1993 :

Low Reynolds number k-E modelling with the aid of direct simulation data

Rodi and Mansour

JFM vol 250 pp 509-529 - 1993

And you may take a look at jobs done by Durbin and co, the keyword should be elliptic relaxation.
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Old   July 11, 2001, 11:23
Default Re: One-/Two--equ--turbulence-model
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Matthias
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Thanks for help

Matthias
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