Zoom-Webinar: Transition Modeling and Phenomenology – 9.7.2020, 20:00-22:00 (IDT) + Unabridged Recording

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! ????

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.

(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).

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.

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.

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 ??)...

Zoom-Webinar: Transition Modeling and Phenomenology – 9.7.2020, 20:00-22:00 (IDT) + Unabridged Recording

May all of you and your loved once keep safe and healthy at this turbulent (Hopefully transitional and not violent inviscid instability type of times ?)