I have seen as early as 80 years ago some hot wire probles were used in measuring the transitional flow on aircraft external flow. In wind tunnel experiment, the freestream turbulence intensity, size of the turbulence vortices, sound level of the tunnel were known to affect transition measurement. Nowadays, researchers are capable to use PIV and LDA methodology to measure the detail velocity field. I can see researchers can also determine the normalised Reynolds shear stress distribution. A thresthold of 0.1% can be used as the transition onset position.

If transition is considered in the aircraft design, then designers need to know the transition effects and to have a calculation tool capable of predict transition. Few researchers are close to the truth of transition, and nowadays engineers have to using engineering ways to calculate transition. A well known method is eN method, with many assumptions and limitations. The method was based on linear stability theory. In Computational Fliud Dynamics computations, RANS approach requires turbulence models to close the equation system. Turbulence models, as the name indicates, deal with turbulent flows. In the development of turbulence model, low Reynolds number correction, correlation based method, intermittency factor are consided currently. In all above methods I mentioned, transition prediction is a myth: transition position is not predicted but reproduced from empiricl relationships.Transition is rather complex. Once your understand transition in imcompressible flow, more problems will incur when moving to compressible flow.

The state of the art CFD calculation method is hybrid LES-RANS approach, such as improved delayed detached eddy simulations. I am not clear how LES deal with transition. It looks there's no sepcial manners. Direct Numeric Simulations require tremendous computing resources. Some results are also available from university labs. Transition can also be modeled.

Unfortunately, I am not a person who investigate transition. How do I know this? :)

My phd thesis was on turbulent spot structure in transitional 3-D flow (you may see my paper in J. of Fluid Mechanics, (1996), 329:1-24). I worked with Prof. R. Narasimha who is a genius in different fluid dynamics topics namely transitional flow. I am aware of most of matters you mentioned above, but I am in search of a practical way to predict transition in different flight configuration of an transport aircraft like, take off, cruise and landing.

A recent review paper which may be worth a look: http://www.sciencedirect.com/science/article/pii/S0376042112000851

As far as I know, the newly developed gamma-Re_theta SST model is popular these days. But I am not certain about how does current aircraft design recognize this model. A validation case was performed by ANSYS company in the regular AIAA high lift prediction workshop. The three element airfoil is a kind of take-off or landing configuration.

Robin B. Langtry and Florian R. Menter. "Correlation-Based Transition Modeling for Unstructured Parallelized Computational Fluid Dynamics Codes", AIAA Journal, Vol. 47, No. 12 (2009), pp. 2894-2906.

I think you should have more knowledge than me on transition understanding since your PhD work was on that. I considered transition for just a few months, and my project is not on that. If I have somewhere stating not correct or not proper, I am in return happy if you can criticize.

Thanks for your comments.