Dr Faustus of Modern Physics - Department of Speech, Music and ...

Chapter 38
Boundary Layer: Prandtl
Prandtl’s control of mathematical method and tricks was limited.
(Von Karman, Prandtl’s student)
38.1 Ludwig Föppl, Prandtl’s Teacher
• By that time, there had been no theoretical explanation for the drag experienced
by a body in a flowing liquid or in the air. The same applies to the lift
on an airplane. Classical mechanics was either based on frictionless flow,
or, when friction was taken into account, mathematical difficulties were so
enormous that hitherto, no practicable solution had been found. Prandtl’s
idea that led out of this bottleneck was the assumption that a frictionless
flow was everywhere with the exception of the region along solid boundaries.
Prandtl showed that friction, however small, had to be taken into account in
a thin layer along solid walls. Since that time, this layer has been known
as Prandtl’s boundary layer. Prandtl could prove theoretically and experimentally
that the boundary layer can separate from the surface of a body
immersed in a flowing fluid at suitable points, to roll up and leave the body
as an isolated vortex.
38.2 Von Karmann
• Prandtl, an engineer by training, was endowed with rare vision for the understanding
of physical phenomena and unusual ability in putting them into
relatively simple mathematical form. His control of mathematical method
and tricks was limited; many of his collaborators and followers surpassed
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