Prandtl, Ludwig (1875–1953)

German physicist who put fluid mechanics on a sound theoretical basis and originated the boundary-layer theory. His work in aerodynamics resulted in major changes in wing design and streamlining of aircraft.

Prandtl was born in Freising, Bavaria, and studied at the Technische Hochschule in Munich. In 1901 he became professor at the Technische Hochschule in Hannover; from 1904 he was professor of applied mechanics at Göttingen. There he constructed the first German wind tunnel in 1909 and built up a centre for aerodynamics.

In a paper of 1904, Prandtl proposed that no matter how small the viscosity of a fluid, it is always stationary at the walls of the pipe. This thin static region or boundary layer has a profound influence on the flow of the fluid, and an understanding of the effects of boundary layers was developed to explain the action of lift and drag on aerofoils during the following half century. In 1907, Prandtl investigated supersonic flow.

In 1926, Prandtl developed the concept of mixing length – the average distance that a swirling fluid element travels before it dissipates its motion – and produced a theory of turbulence.