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Ansys 12, Fluent, SST Transition models

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Old   July 12, 2010, 03:31
Default Ansys 12, Fluent, SST Transition models
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B. Selenbas
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Hi,

I'm working on a laminer-turbulence seperation problem and want to use the new transition models in Fluent (ansys 12) version. I could not find any guide that presents the related equations. Has anybody got any information about these new turbulence models?

Thanks
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Old   July 12, 2010, 10:17
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Take a look in the CFX documentation (you'll have to install CFX). The formulation is there and should be the same as Fluent.
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Old   July 13, 2010, 06:25
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Bugra,

I think that this may helps you:

Boundary Conditions/Inlet/Intermittency (this is an relative coo. value on upper airfoil curve (from 0 to 1) and represents transition point).
You need to know that value from some documentation or Xfoil simulation gives the answer.

All the best,
NV
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Old   July 13, 2010, 08:13
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The idea of the Gamme Theta (Langtry Menter) transition model is that you don't need to know your transition location - it's predicted as part of the simulation.
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Old   July 13, 2010, 14:55
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I have a little practice in CFX but I'll try this model, of course.
That is nice.

Thanx stumpy!
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Old   July 13, 2010, 14:57
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I think that model should be in Fluent now too?
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Old   July 16, 2010, 05:11
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Some corection by myself:

Intermittency Factor is a measure of the probability that a given point is located inside a turbulent region. Upstream of transition the intermittency is zero. Once the transition occurs, the intermittency is ramped up to one until the fully turbulent boundary layer regime is achieved.

All the best,
NV
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Old   July 29, 2010, 11:58
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In CFX, there is the option for transition with the SST model. The recommended transition model is the Gamma Theta Model developed by Langtry and Menter, which has been developed for standard bypass transition and low free-stream turbulence. The full transition model is based on two transport equations, one for intermittency and one for the transition onset criteria in terms of momentum thickness Reynolds number. There are other choices in CFX as well. The CFX documentation says that this model has been widely validated.
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Old   July 29, 2010, 12:04
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The FLUENT documentation states:

The transition SST model is based on the coupling of the SST k-omega transport equations with two other transport equations, one for the intermittency and one for the transition onset criteria, in terms of the momentum thickness Reynolds number. An empirical correlation by Langtry and Menter has been developed to cover standard bypass transition as well as flows in low free-stream turbulence environments.

It looks like the same SST transition model is available in CFX and FLUENT, which is not surprising.

It looks like FLUENT also has another transition model available called the k-kl-omega transition model. It is considered to be a three-equation eddy-viscosity type, which includes transport equations for turbulent kinetic energy, laminar kinetic energy and the inverse turbulent time scale.
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