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

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Old   April 17, 2013, 23:07
Default 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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Old   April 18, 2013, 00:54
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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.

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Old   April 18, 2013, 03:34
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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!
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Old   April 18, 2013, 04:56
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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...
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Old   April 18, 2013, 07:40
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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.

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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.
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Old   April 18, 2013, 08:59
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can you send these papers to turboenginner@gmail.com
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Old   April 18, 2013, 23:22
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Sent, cheers

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Old   April 18, 2013, 23:53
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Oj

Thanks a lot.
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