Perspective on the Prandtl Medal: Model vs Reality

                Prandtl with his model of reality in the form of a little water tank in Göttingen in 1904.

The Prandtl Medal to be given to me (and my coworkers) on July 21 in Barcelona connects to the basic question in science and engineering of model vs reality: As far as I can understand the award expresses a recognition of our work showing that the basic idea of Prandtl of the boundary layer as the origin of lift and drag of an airplane wing, is incorrect.

Our evidence is computed solutions of the Navier-Stokes equations with slip boundary condition, which does not give rise to any boundary layers, but yet fit closely with observations. The agreement improves with increasing Reynolds number beyond $10^5-10^6$, because slip models a turbulent boundary layer. For a jumbojet the Reynolds number is $10^8$ or larger.

More precisely, the computations with slip show somewhat better lift and stall characteristics (higher lift and delayed stall) than experiments.

There are two basic approaches to handle a difference between model and reality: Change the model or change the reality. The second option represents an engineering approach with the goal of constructing a wing so as to realize slip also for moderately large Reynolds numbers (of size $10^5$). One way of doing that is to use rotating cylinders at leading and trailing edge and/or a moving upper wing surface, which indeed shows to improve both lift and stall.

The Prandtl Medal thus invites to redesign of wings according to the model, rather than changing the model to represent existing wings constructed in the spirit of Prandtl as the Father of Modern Aerodynamics.

See also:

• The Spell of Prandtl's Laminar Boundary Layer
• The Spell of Kutta-Zhukovsky Circulation Theory.

Obama vs Developing Countries and Refrigerators

Obama revealed to graduates at UC Irvine the reasons behind his climate policy:

• I’m going to talk about one of the most significant long-term challenges that our country and our planet faces: the growing threat of a rapidly changing climate.
• Developing countries are using more and more energy, and tens of millions of people are entering the global middle class, and they want to buy cars and refrigerators. 
•  So if we don’t deal with this problem soon, we’re going to be overwhelmed. These nations have some of the fastest-rising levels of carbon pollution.

Obama seeks support among students to "deal" with the problem of a rapidly growing middle class around the globe demanding refrigerators as a necessary means to improve living standard.

The Ludwig Prandtl Medal

Today I received the following message:

Dear Professor Johnson, It is our great pleasure to inform you that you are the winner of the 2014 edition of the ECCOMAS Ludwig Prandtl Medal. The decision has been taken by the ECCOMAS Award Committee in a two-round voting procedure. Please receive our warmest congratulations. 

The Ludwig Prandtl Medal will be delivered at the Opening Session of the WCCM-ECCM-ECFD 2014 Conference in Barcelona, July 21, 2014 (8:30-10:30). We would very much appreciate if you can confirm your participation.

With our best regards and congratulations,

Ekkehard Ramm
ECCOMAS PresidentJosef Eberhardsteiner
ECCOMAS Secretary

Here is my answer:

Dear Profs Ramm and Eberhardsteiner

Thank you for this great honor, which I will be very happy to receive in person at the conference opening. 

The award has an interesting aspect from scientific point of view in that my work (with Johan Hoffman), shows that Prandtl's main idea of the fundamental role of the boundary layer, for both separation and drag and lift, crowning him as the Father of Moden Fluid Mechanics, is incorrect. We show that separation, drag and lift originate from instability of slightly viscous flow and not from a boundary layer. The evidence comes from solving the Navier-Stokes equations with slip boundary condition, which does not give rise to any boundary layer, and we obtain results in full agreement with observations. We conclude that separation, drag and lift in slightly viscous flow do not originate from a boundary layer and thus that Prandtl's main idea is not in agreement with observations.

I would appreciate if this will be made clear to the public at the conference and I would certainly be willing to shortly expose the reasons why Prandtl was wrong. 

The fluid dynamics community will not applaud the award, since 20th century fluid mechanics has followed the Father in search of the origin of separation, drag and lift in the boundary layer. This has had a catastrophic impact on computational fluid mechanics leading to the strong belief that correct results require resolution of boundary layers, which however is impossible even in thinkable future since quadrillions of mesh-points would be required. The result is a dead-lock of rational science. We show that drag and lift of an airplane can today be accurately computed over the entire range of angles of attack including stall, by solving the Navier-Stokes equations with slip using a couple of millions of mesh points. 

The award thus brings a major scientific question to the podium and I hope it can be accompanied by a scientific discussion.
Sincerely, Claes Johnson

Lena Andersson om Grundorsaken till Skolans Kris

Lena Andersson ger i dagens DN en insikstfull skarp analys av grundorsaken till den djupa kris inom svensk skola, som så så många omvittnar men så få vill förstå och ingen vet någon lösning på:    

• De dystra rapporterna från skolan ger upphov till frågan om inte felet sitter i det absurda mötet mellan auktoritärt och antiauktoritärt.
• Tanken borde åtminstone prövas att skolans tvång och likriktning är vad som hämmar just motivationen och insikten. 
• Fundamentet för skolan är auktoritärt, bokstavligen instängande. 
• Eftersom tvång och straff hör dåtiden till och övriga samhället går mot autonomi och frivilliga avtal gör skolans modernt sinnade personal vad den kan för att kompensera formernas hårdhet med mjukhet i innehållet.
• Skolans upplösthet möjliggörs av de antiauktoritära formerna, men orsakas inte av dem.
• Orsaken står snarare att finna i krocken mellan oförenligheterna tvång och löshet. 
• Genom psykologi­vetenskapen och erfarenheten vet vi att människor reagerar mycket dåligt på relationer av dubbelbindande natur, exempelvis föräldrar som säger ett och visar ett annat, och där det inte undgår barnet vad som sägs i mellanrummet och att det gör fel hur det än gör
• Varför skulle man inte reagera likadant på en psykologiskt dubbelbindande institution som upptar så många år av ett ungt liv?

Detta är vad jag själv försökt uttrycka men ingen velat lyssna på. Frågan är om någon vill lyssna på LA? 

Matematik är skolans hårdaste kärnämne där krocken har sitt tydligaste uttryck. Utbildningsminister Jan Björklund, som ingenting begriper av vad LA säger, satsar nu miljarder på att lära alla svenska elever bråkräkning i ett tvingande Matematiklyft, som alla inblandade redan vet kommer att misslyckas. 

I detta lyft ingår ingenting av den IT-Matematik som skulle kunna ge mening åt matematikämnet för många av de elever som nu är dömda att stämplas som icke godkända i för dem meningslös exercis, med vida konsekvenser för självbild och livsprojekt. 

Vill Matematikersamfundet Diskutera Skolans Matematikundervisning?

Redaktör Per-Anders Ivert uppmanar Sveriges yrkesmatematiker, enligt önskemål på denna blogg, i majnumret av Svenska Matematikersamfundets medlemsblad Bulletinen, att engagera sig i diskussion av matematikundervisningen i dagens skola.  I väntan på inlägg i Bulletinens nästa nummer, som kommer till hösten någon gång, inbjuder jag nu till diskussion här.

Hoppas att någon är intresserad av att uttrycka någon tanke om skolmatematiken, som ägnas så mycket möda och tid och som anses vara så viktig för Sveriges överlevnad som kunskaps och teknik-samhälle.