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Old   November 10, 1999, 08:16
Default mixing length moodel
  #1
tomi
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Hi everyone,

I am working on the implementation of a mixing length turbulence model to calculate recirculating free-surface flows. I would appreciate any recommendations, suggestions, hints about algorithms and literature. I look forward to your response.

have a nice day

tomi
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Old   November 11, 1999, 16:52
Default Re: mixing length moodel
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Andrzej Matuszkiewicz
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Do you think that a simple mixing length model is enough to describe a complicated wave-turbulance ineraction at the gas-liquid interface? I know there have been a number of experimental research in this area but I haven't seen any published model. I have been using Prandtl model at the both sides of the interface, but I think we need something more sophisticated.

Andrzej
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Old   November 12, 1999, 06:12
Default Re: mixing length moodel
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tomi
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Andrzej,

You are certainly right. but this model is nice to start off with since it's pretty easy to understand. k-e might be more appropriate but how do you handle all 5 constants? change them for every situation or leave them as they are and hope your results won't be affected? anyhow, thanks for your response

thorsten
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Old   November 12, 1999, 07:44
Default Re: mixing length moodel
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Dr. Hrvoje Jasak
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Hi,

I've got a bit of a problem here: in order to do RANS turbulence modelling, you decompose the velocity into the mean and oscillatory part (good). But what happens with the free surface?? It moves with the instantenous velocity and NOT the mean (i.e. the one you haven't got). The only honest thing you could do is to say that you're no longer solving (or tracking) the free surface, because it has no "mean" position. The best you can do is to replace by the probability density function of the free surface, which gets you in the right mess in terms of turbulence interaction. Have you any thoughts on this problem?

Hrvoje
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Old   November 12, 1999, 10:00
Default Re: mixing length moodel
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John C. Chien
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(1). I think, what is going on under the free surface is its own business. (2). Under the mixing tank, the flow will be turbulent, but on the surface, the TKE is zero. Then the mean is the transient varaible. (3). If the surface begin to dance, it will break away, turn into droplets and evaporates.
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Old   November 12, 1999, 12:24
Default Re: mixing length moodel
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Andrzej Matuszkiewicz
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Thorsten,

If it is of any help I can send you hardcopies of my two papers on a counter-current gas-liquid flow. You can find there results on the mixing length model applied to the gas-liquid interface as well as references to a few mixing length functions.

Andrzej
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