# Teta term in Menter's Momentum thickness Reynolds number equation for transition

 Register Blogs Members List Search Today's Posts Mark Forums Read

 June 28, 2012, 18:56 Teta term in Menter's Momentum thickness Reynolds number equation for transition #1 New Member   Adrian Join Date: Mar 2012 Posts: 8 Rep Power: 6 Hi, I'm currently undertaking a task of implementing the gamma-Re transition formulation for turbulence modelling by way of a UDF in Fluent. I've come across a problem. There's lambda term in used for prediction of transition onset, denoted lambda underscore theta. In the formulation of this term, a parameter given by a capital theta is required. (equation 28 in Langtry & Menter, 2009, 'Correlation-based transition modelling for unstructured parallelized computations CFD') The problem is, that in all the literature I have looked in, no correlation or formulation for this term is given. As you would expect, this has brough my progress to a standstill. I would be grateful if anyone could suggest where I might be able to look for an answer. Many thanks.

 June 28, 2012, 20:09 #2 Senior Member   Mehdi Join Date: Jan 2011 Location: Iran Posts: 130 Rep Power: 7 it should be calculated iteratively. you should take following step: 1-guess teta (teta=0) 2-find F(lateta) and Rethetat (from form. 35-38) 3-find theta from Retheta (Retheta=ru*theta*U/mu - you can see it in Nomenclature) 4-go to step 2 and iterate until it converge. I hope I can explain it well. __________________ Best Regards; Mehdi E-mail: mb.pejvak[at]Gmail[dot]com

 June 29, 2012, 09:53 #3 New Member   Adrian Join Date: Mar 2012 Posts: 8 Rep Power: 6 That makes it much clearer. Thanks very much.

 June 29, 2012, 10:02 #4 New Member   Adrian Join Date: Mar 2012 Posts: 8 Rep Power: 6 Just one thing, to calculate theta in step three, which value for Retheta do I use? Do I make it equal to Rethetat?

 June 29, 2012, 12:10 #5 Senior Member   Mehdi Join Date: Jan 2011 Location: Iran Posts: 130 Rep Power: 7 I am sorry, i made a mistake. In fact, Rethetat is true in step three instead of Retheta. __________________ Best Regards; Mehdi E-mail: mb.pejvak[at]Gmail[dot]com

 June 29, 2012, 12:35 #6 New Member   Adrian Join Date: Mar 2012 Posts: 8 Rep Power: 6 But then Rethetat is calculated using thetat, whereas lambdatheta is calculated using just theta.

 June 29, 2012, 22:35 #7 Senior Member   Mehdi Join Date: Jan 2011 Location: Iran Posts: 130 Rep Power: 7 yes that is true, but in calculation of landa it was recommended to Theta= thatat. In fact, I have never understand why and in all paper and thesis I have read, never describe its reason. if I complete my former reply, following steps can explain it better: (a) guess the initial value for Thetat (=0 was recommended) (b) calculate the Landa by setting Theta= thatat (c) calculate the Flanda (d) calculate the Rethetat (e) calculate the t from the definition of Thetat =(no/U)Ret. (f) go to step 2 and iterate until it converge. The calculation may converge in a few iterations. __________________ Best Regards; Mehdi E-mail: mb.pejvak[at]Gmail[dot]com Last edited by mb.pejvak; June 30, 2012 at 01:11.

 July 1, 2012, 12:31 #8 New Member   Adrian Join Date: Mar 2012 Posts: 8 Rep Power: 6 I'll try that out. Many thanks for your help.

 July 14, 2012, 15:29 #9 New Member   Adrian Join Date: Mar 2012 Posts: 8 Rep Power: 6 A friend of mine is also implementing the Transition formulation of Menter for the Spalart Allmaras turbulence model based on the paper by Medida and Baeder 'Application of the Correlation based gamma-retet Transition Model to the Spalart-Allmaras Turbulence model' and has encountered a problem with the blending function. In the paper it is specified that the blending function is used to distinguish a wall boundary layer and a free shear layer to deactivate the production term in the wall boundary layer only. However, this function depends on the dissipation rate, which is not available in the S-A model. The paper says that the blending function has been turned off manually, but does not explicitly specify how this is done. Can anyone suggest how this is done? Any help would be greatly appreciated.

 November 30, 2012, 20:30 #10 New Member   patty Join Date: Nov 2010 Posts: 21 Rep Power: 7 Adrian, I am trying to put in the SA transition model currently also. I ran into the same problem with how to handle the F_theta blending function. Do you know how your friend ended up resolving that?

 Tags menter, omega, sst, transition

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post bobburnquist OpenFOAM Native Meshers: snappyHexMesh and Others 6 August 26, 2015 09:38 laliong Main CFD Forum 11 March 19, 2015 12:42 Sas CFX 15 July 13, 2010 08:56 Prakash Main CFD Forum 0 June 13, 2008 10:45

All times are GMT -4. The time now is 22:47.