Considered the father of modern fluid mechanics.

Ludwig Prandtl was born in Freising, Germany, in 1875, and studied mechanical engineering in Munich, Germany. After receiving his doctorate from the Munich Technische Hochschule in 1900, Prandtl worked at a factory in Nürnberg, Germany, before becoming professor of mechanics at the Technische Schule in Hannover. In 1904, German mathematician Felix Klein encouraged Prandtl to accept the position of professor of applied mechanics at the University of Göttingen, where Prandtl remained for almost a half-century. Because of Prandtl’s groundbreaking work in fluid mechanics, Göttingen developed into an internationally renowned center of aerodynamic research.

Prandtl’s 1904 discovery of the boundary layer resolved the issue of fluid friction. Prior to Prandtl’s work, scientists had been unable to understand or explain the frictional forces of viscous fluids, especially water and air. Through experiments with a small water tunnel, Prandtl proved the existence of a boundary layer in fluids flowing around a solid structure, such as water in a pipe or air over a wing. He defined the boundary layer as the region of the flow adjacent to the wall of a solid surface, where the viscous effects cause the molecules of the fluid to stick to the wall. Any solid body, such as a boat, airplane, car, or machine part, moving in a viscous fluid, such as water or air, creates a boundary layer around it. Prandtl’s theory explained that friction, or drag, at the wall of the solid body is due to the presence of the boundary layer. His breakthrough led to the development of the science of fluid dynamics. The boundary layer theory was initially applied to laminar, or nonturbulent, flows, but Prandtl’s later experiments in 1914 demonstrated that the boundary layer also exists in turbulent flows. The boundary layer theory helped scientists design machines and devices to account for the drag that results from the boundary layer.

Prandtl’s work on friction drag resulted in his 1918 development of wing theory, which explained the flow of air over airplane wings. The Lanchester-Prandtl wing theory, named for both Prandtl and the British physicist Frederick Lanchester, whose simultaneous work was independent of Prandtl’s, calculates the lift on the wing. Prandtl’s other numerous contributions include his work in supersonic and subsonic flows and turbulence and in wind tunnel design. Prandtl’s contributions to aerodynamics eventually led to manned flight and earned him the title of father of aerodynamic theory. After falling ill in 1952, Prandtl died in Göttingen on August 15, 1953.

• Prandtl, Ludwig. Essentials of Fluid Dynamics, with Applications to Hydraulics, Aeronautics, Meteorology, and Other Subjects. New York: Hafner, 1952. A technical volume that provides an in-depth look at Prandtl’s work in fluid dynamics and other areas throughout his long career.
• Schlichting, Hermann. Boundary Layer Theory. 6th ed. New York: McGraw-Hill, 1968. A fluid mechanics text with many references to Prandtl and to his students, including a good discussion of his involvement in viscous flow theory, with detailed chapters about laminar and turbulent boundary layers.
• Sundaram, T. R. “The Father of Aerodynamics.” World and I 12, no. 11 (November, 1997). Profiles Prandtl, his early work in airflow modeling, boundary layer theory, and his later career.

Aerodynamics

Airfoils

Forces of flight

Wind tunnels