Ludwig Prandtl, 1875-1953

Abstract

It is a tragedy in our age of technological evolution that those who initiate progress in important fields so often live to see their results applied to quicker and more thorough destruction. Certainly aviation is one of those dubious blessings. And the father of aerodynamics, Ludwig Prandtl, familiar since his youth with treasures of art and architecture in the lovely old city of Munich, doubtless could not help being haunted by the thought of why the day, on which mankind learns how to fly, must be the last day for many of these creations. In heavier-than-air aviation, which Prandtl advanced by advocacy of wide-span monoplanes, he was not himself a pilot, while in the lightcr-thanair department, in which he fathered the streamline shape of dirigibles, he was at least a licensed practising balloonist. But he was not even a passenger in an airplane until about 1930, and his aerodynamical laboratory flourished without any connexion to an airfield. Prandtl preferred a small staff of rational thinkers and was almost afraid of the emotional interference which comes with the touch of the stick and with real flying. In no way does that mean that all play and fun were taboo at work. On the contrary, Prandtl's own way to tackle the Navier-Stokes equations was to toy with flows far beyond the range of practical application, showing the pleasure and also the marvelling observation of a child, till a phenomenon crystallized that asked for explanation. Spheres and cylinders were used as models—there would be no ‘Karman vortex street’ without that—sharp-edged corners were preferred to complicated shapes. He liked to reduce the number of arbitrary shape parameters, etc., so the brain would have no excuse for misinterpretation. The growth in time of starting vortices or of the curling ends of discontinuity layers, or the steady supersonic flow around the corner, are famous examples without any geometrical length, as indeed is the development of the boundary layer from the edge of a flat plate.