# How can you tell at which point the flow transitioned from laminar to turbulent on an

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April 17, 2013, 23:07
How can you tell at which point the flow transitioned from laminar to turbulent on an
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ok I just have one basic question here... How can you tell at which point the flow transitioned from laminar to turbulent? I know we can do u+ vs y+ for a flat plat boundary layer profile. But for an airfoil/turbine cascade that is curved...what is the method? My geometry is attached below
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 April 18, 2013, 00:54 #2 Senior Member   OJ Join Date: Apr 2012 Location: United Kindom Posts: 475 Rep Power: 13 The shear in laminar boundary layer is smaller while that in turbulent one is larger. How about plotting a skin friction coeff along the curved wall? A big jump in it should indicate the transition. OJ

 April 18, 2013, 03:34 #3 New Member     ram Join Date: Apr 2013 Posts: 10 Rep Power: 6 there is no laminar flow in fact and all turbulent models can solve so called laminar flow, so u should consider all field as turbulent specially in geos like turbines!

 April 18, 2013, 04:56 #4 Super Moderator   Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,358 Blog Entries: 6 Rep Power: 45 You can plot intermittency, turbulent kinetic energy, turbulence intensity and integral parameters. I don't know how you can use skin friction to infer transition, may it is a good indicator of separation but have no idea about transition. I'd interested to find out that how we can use skin friction...

 April 18, 2013, 07:40 #5 Senior Member   OJ Join Date: Apr 2012 Location: United Kindom Posts: 475 Rep Power: 13 The approach I mentioned is, of course, just one of the many popular ways of judging the transition. When there is enough motivation for transition, the Tollmien-Schalichting (TS) waves are developed in the flow which typically are 2D. The waves produce disturbances and slowly they grow into 3D structures giving rise to local vortices etc creating a high shear region. Skin friction coefficient is of course a measure of this shear. Hence its plot on streamwise direction provides a point where the skin-friction shoots up, an indication of transition. OJ Ref: Castelli, M. Raciti, G. Grandi, and E. Benini. "Numerical Analysis of Laminar to Turbulent Transition on the DU91-W2-250 airfoil." Hanjalic, K., Y. Nagano, and S. Jakirlic. "The application of laminar kinetic energy to laminar-turbulent transition prediction." Johansen, Jeppe, Jens N. S-oacute, and rensen. "Prediction of laminar/turbulent transition in airfoil flows." Journal of aircraft 36.4 (1999): 731-734. Far likes this.

 April 18, 2013, 08:59 #6 Super Moderator   Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,358 Blog Entries: 6 Rep Power: 45 can you send these papers to turboenginner@gmail.com

 April 18, 2013, 23:22 #7 Senior Member   OJ Join Date: Apr 2012 Location: United Kindom Posts: 475 Rep Power: 13 Sent, cheers OJ

 April 18, 2013, 23:53 #8 Super Moderator   Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,358 Blog Entries: 6 Rep Power: 45 Oj Thanks a lot.

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