A webinar on my favorite topic 💕 – Transition.

I am always amazed over and over again when you participants find the time to watch me talk, I feel a wholeheartedly flattered but mostly grateful. Thank you! 🙏💕

There is quite a lot of research and known facts about turbulent flows and of course the laminar ones, yet the transition between them was always  a lacking in knowledge and enigmatic phenomena.

It doesn’t matter which kind you prefer in the above video…

In this short webinar we really really flew at a fast pace around very deep topics like the history of transition beginning with Reynolds and Orr-Sommerfeld, but also after noting ?Rayleigh and Fjo’rtof and 2D inviscid laminar flows criterions moved to 3D base flows and saw indications for baseflow profiles which arrive to a turbulent state without having an inlection point, that led us to the option of searching an answer in interacting mechanism of both Orr-Sommerfeld and Squire equation, and not stick with modal groth, with Ellingsen and Palm (1983) we have found transient algebraic growth, and introduced the reynolds-Orr Equation and learned firmly that the grothh rate of a final inviscid flow transition and and the inflection point and Fj’ortof Criterion. Modal stability analysis and the Orr-Sommerfeld/Squire equations, Landahl’sLift-up effect (1980 MIT school), and its huge contribution.

Yes, I did that, Google didn't satisfy me in these case

(highly) non-normal linearity Vs.non-linear normality where explained in a couple of ways,

“bootstrapping debate” (Fabian Walleffe clearly quite harshly criticizing the school of thought originating in MIT and spreading to KTH). At the time was fully engrossed with non-normal operators and linear transient growth mechanisms… Than it hit me that Walleffe has it very nicely explained, a rush of confusion went through my body. It made me review how much we do not notice our tendency for confirmation bias (in a big way unconsciously).

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I think that if one listens well the concepts of streaks becomes almost fully explained.

secondary instability theory and Floquet analysis, the concept of pseudospectra “(read

his book like crazy – one of my best involving math and physics) and LLOyd Trephten

with the amazing conceptuality and relevence to transition flow of the Pseudospectra

and the behaviour of a resolvent when a non-normal or better yet HIGHLY non-normal

operator is where we aim to investigate. that the level of non-normality could be

represented represented by a condition number, of which the non-normal matrix

behaviour dependents strongly, we simply don’t have the same behaviour for the

resolvent of a normal Vs. a non-normal operator… and if we understood the essence we

MUST acknowledge that in the case of transient growth of non-normal operators things

like shpe (the obliqueness of Dan Henningson (KTH), the Landahl’s effect, and

‘bootstraping” redistributing energy in orthogonal direction back and forth) play a huge

role and it is not the exponentially modal eigenvalue that is not most susceptible to

growth just enough to excite non-linear mechanisms.

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We saw that a spectra of an undisturbed initial flow to a infinitesimal disturbance is

modaly stable or perhaps unstable by way such a way that we shall find the flow

turbulent way before the representing Reynolds number of the unstable orthogonal

mode happens (such as waiting for orszag (1971) to find that at 5777.2 while in actuality

transition arrives whey before distabilation…). trying to communicate the essence

without deriving (albeit sometimes getting a glimpse at the frightening equations to stay

attached to the core)…

Then get a short but well posed acquaintance with types of transition mechanisms, (K-H-

O-N-TS…) the evolving literature in the studying fine grained coherent structures and self

sustained turbulence cycles, and watch cool KTH (by one of my favorite dissertations

ever of Phillip Christian Schlatter…) and P. MOIN LES and DNS.

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It was really hard to organize communicating such an intrinsically intricate topic in two

hours. So I must admit I had some live difficult time… 🙏 (Forgive me if I got a little

confusion, you know this rarely happens to me… Love me 😋)…


 ✨There is room for a second webinar on the topic. Next week seems cool…✨



DNS of a zero-pressure-gradient flat plate boundary layer (P. Moin and X. Wu)
DNS of a zero-pressure-gradient flat plate boundary layer (P. Moin and X. Wu) – “ZPGFBGL”

The webinar presented many recommended resources that I find most valuable. Resources shall are shared as per request with participants, and it is always said they may always reach out tome without thinking a second time, helping you is never time wasted. that  and the webinar shall be unabridged recorded. 

The webinar, as all of my webinar is interactive, always asking participants not to unmute themselves, still ending with a dedicated Q&A.

Register for the next TRANSITION tour…

There is room for a second webinar on the topic. Next week seems cool…✨


Unabridged recording, All the gratitude to my friend and colleague Rajat Walia: 



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