Background

Ludwig Prandtl was born on February 4, 1875, in Freising, Germany, the only child of Alexander Prandtl, an engineering professor at the agricultural college at Weihenstephan. Owing to the protracted illness of his mother, the former Magdalene Ostermann, he was particularly close to his father, who led him early in life to an interest in natural phenomena.

Education

A bright child, Ludwig could count to 10 by the time he was four years old and he could read by the age of five. He started attending elementary school in the autumn of 1881 when he was six years old. He was an outstanding pupil, coming top of the class of 82 pupils in his first year and continuing to be ranked first throughout his elementary schooling. He began his secondary education at the Gymnasium at the Freising Domberg in September 1885.

In 1888 Prandtl was sent to the Ludwig Gymnasium in Munich. This was the second oldest Gymnasium in Munich, founded in 1824. He lived in a dormitory at the school but this was not a good experience for the 13-year old Prandtl who was bullied by the older boys. After one year at the school, his father decided that Prandtl should return to the Gymnasium at Freising. After two years, he returned to the Ludwig Gymnasium in Munich where now he was more able to fit in and make good friends. He excelled at Latin, Greek, and particularly natural sciences. He gained much respect from his classmates. He graduated from the Gymnasium in July 1894 and he went to Nuremberg where he spent three months gaining practical experience working in a foundry.

Returning to Munich, in 1894 Prandtl entered the Technische Hochschule at Munich to study engineering. He graduated in 1898 and two years later completed his doctorate under the famous mechanic's professor, August Föppl, who had been one of his undergraduate teachers.

Prandtl wrote his doctoral thesis Lateral displacement phenomena, a case of unstable elastic equilibrium while working as Föppl's assistant. It was a piece of work that he carried out without any formal thesis advisor. The topic was of his own choosing. Although he had completed his thesis by 1899, the Königlich Technische Hochschule did not have the right to award doctorates so he submitted his thesis to the University of Munich. Ferdinand von Lindemann was appointed as an examiner and the oral conducted on 29 January 1900. He was given the grade "very good" and graduated with his doctorate.

Career

After his graduation from Munich University, Prandtl went to work in the Maschinenfabrik Augsburg-Nürnberg, where he was asked to improve a suction device for the removal of shavings. In the process of greatly improving the device, he came to recognize some basic weaknesses in the current understanding of fluid mechanics. One weakness was the inability of existing fluid mechanics to explain why the moving fluid in a pipe would separate from the wall in a sharply divergent section instead of expanding to fill the pipe. In the course of the next three years, Prandtl attacked this problem in a way that was to be characteristic of his later work.

After accepting a professorship at the Hannover Technische Hochschule in 1901, Prandtl proceeded to ask what the missing element in the existing analyses of pipe flows might have been. By 1904 he had developed his celebrated paper on the flow of fluids with small viscosity. In it, he showed that no matter how small the viscosity was, the fluid had to be stationary on the walls of the pipe. Thus the classical theory of inviscid fluids could never be employed without taking cognizance of the way in which a thin viscous region near the wall shaped the flow. An understanding of this region, the boundary layer, was to facilitate the subsequent explanation of lift and drag on airfoils and aspects of almost all other aerodynamic behavior. Prandtl’s insight thus led him to the large problem that lay behind a small one, and he set in motion a program of theoretical and experimental research that is still being worked out today.

By this time a new wind had begun to blow through the German system of higher education. The mathematician Felix Klein, feeling that the gulf between mathematics and technology was too wide, had established several technical institutes at Göttingen University. On Föppl’s recommendation, Klein gave Prandtl a chair at Göttingen and placed him in charge of the Institute for Technical Physics. Just after this move Prandtl’s presentation of the boundary layer paper at the Third International Congress of Mathematicians at Heidelberg won high praise from Klein, who was quick to understand what his new man had accomplished.

At Göttingen, Prandtl had very good graduate students and access to the resources and interest of the industry. He also was encouraged to pursue more theoretical lines of research than he had been at Hannover. During his first years there he made lasting contributions to the theory of supersonic flow. He combined Riemann’s theories with Mach’s Schlieren flow visualization apparatus to obtain the first explanation of the behavior of supersonic nozzle efflux. Later he was responsible for the first mathematical description of supersonic flow around slender bodies. He also was instrumental in developing the first German wind tunnel, which was completed at Göttingen in 1909.

Meanwhile, in the autumn of 1906, Prandtl’s most notable student arrived in Göttingen. Theodore von Kármán sought Prandtl out to direct his research on the theory of nonelastic buckling. He was only six years Prandtrl’s junior; and their lives and pursuits touched many times between 1906 and their last meeting in 1945, when Kármán, a Hungarian Jew who had become an American citizen, returned to Germany with an army interrogation team.

Prandtl’s aerodynamic work developed steadily from 1909 to the end of World War I. Between 1909 and 1912 he helped to establish test codes for fans. In 1914 he explained a puzzling, sudden drop of the drag coefficient for a sphere that occurred with increasing velocity. He did this by again recognizing the important phenomenon underlying a minor problem: the laminar-to-turbulent transition of the boundary layer on the body.

Prandtl’s most significant contribution during this period was his work on airfoil theory. The lift force on wings was fairly well understood, and he turned to the explanation of drag. The boundary layer gave rise directly to skin friction which was much too small to account for wing drag. In 1911 and 1912 Kármán, stimulated by the experimental work going on in Prandtl’s laboratory, did much to explain another component, profile drag. He described the so-called Kármán street of alternating vortices, parallel with an aerodynamic body, that must be pulled along behind it. Prandtl continued to work on a third contribution, induced drag. He had recognized that the presence of lift causes a trailing vortex to be induced in the shape of a long distorted horseshoe with its base at the airport where the flight began and its ends at the wingtips, which continually generate the vortex.

Prandtl’s attempts to analyze this source of drag subsequently fell under the veil of wartime secrecy, and his descriptions of the effect finally emerged in restricted Göttingen publications in 1918 and 1919. By 1920 the idea reached a larger public and wrought sharp changes in the wing design and streamlining of airplanes. It led in general to more cleanly shaped wings, to higher aspect ratios, to today’s swept-back wings, and to the use of streamlining fillets.

The elusive problem of describing turbulent flow yielded to Prandtl’s and Kármán’s competitive efforts in the mid-1920s. Kármán, who then was teaching at Aachen, discussed the structure of turbulent flows in 1924 but failed to produce a strategy for analyzing it. In 1926 Prandtl provided the conceptual device needed to make an analysis. This was the “mixing length,” or average distance that a swirling fluid element would travel before it dissipated its motion. The idea resembled the notion of a mean free path in the kinetic theory of gases and was used in a somewhat similar way. Subsequent experiments by Prandtl and theoretical work by Kármán made it possible for Prandtl to present a summary paper on the subject in 1933 that is the basis for chapters on turbulence in today’s textbooks.

During the 1930s and 1940’s Prandtl, now an elder statesman of fluid mechanics continued to contribute to the basic literature and technology and reaped honors for his accomplishments. Nevertheless, his interrogation by the United States Army in 1945 found that the mainstream of wartime technology had more or less bypassed Prandtl and Göttingen. Hitler had shown greater interest in rocketry at Peenemunde and the laboratory at Brunswick. The team, arriving in Göttingen from the slave labor camp at Nordhausen, found Prandtl complaining peevishly about bomb damage to his roof and asking how the Americans planned to support his ongoing work.

While the picture is one of a technician who felt little obligation to anyone’s politics, it forms a consistent view of Prandtl, who, after all, made enormous contributions to his world as a technologist. He was then seventy-one and just turning his attention to meteorology, on which he published material as late as 1950.

Achievements

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  Prandtl made decisive advances in boundary-layer and wing theories, and his work became the fundamental material of aerodynamics. He was an early pioneer in streamlining airships, and his advocacy of monoplanes greatly advanced heavier-than-air aviation. He contributed the Prandtl-Glaubert rule for subsonic airflow to describe the compressibility effects of air at high speeds. In addition to his important advances in the theories of supersonic flow and turbulence, he made notable innovations in the design of wind tunnels and other aerodynamic equipment. He also devised a soap-film analogy for analyzing the torsion forces of structures with noncircular cross-sections.
  
  The early history of the Max Planck Institute for Dynamics and Self-Organization is closely linked to the work of the famous physicist Ludwig Prandtl. Prandtl is regarded as the founder of fluid dynamics and especially made a name for himself with his boundary layer theory. In Göttingen Prandtl opened two research facilities that both exist until today: in 1915 the Aerodynamical Experimental Station, which concentrated on application-oriented topics in fluid dynamics and evolved into the Göttinger branch of the German Space Agency DLR, and in 1924 the Kaiser Wilhelm Institute for Fluid Dynamics. The latter mainly dealt with fundamental research in the field of fluid dynamics. After the Max Planck Society was founded the institute was renamed Max Planck Institute for Fluid Dynamics. In 2004 the institute again received a new name and is now called Max Planck Institute for Dynamics and Self-Organization.
  
  Prandtl received many honors for his contributions. He was elected to the Royal Society of London in 1928, having been awarded their Gold Medal the previous year, and received an honorary degree from the University of Cambridge in 1936. Many other universities gave him an honorary degree including the Technische Hochschule Danzig, the Technische Hochschule Zürich, the Technische Hochschule Prague, the Technische Hochschule Trondheim, the University of Bucharest, and the University of Istanbul. He was given honorary membership of the Royal Aeronautical Society and awarded its gold medal. In total over twenty academies elected him to membership. He received a large number of medals and other awards, such as Ackermann–Teubner Memorial Award (1918), Daniel Guggenheim Medal (1930), Wilhelm Exner Medal 1951.
  
  The crater Prandtl on the far side of the Moon is named in his honor. The Ludwig-Prandtl-Ring is awarded by Deutsche Gesellschaft für Luft- und Raumfahrt in his honor for outstanding contribution in the field of aerospace engineering. In 1992, Prandtl was inducted into the International Air & Space Hall of Fame at the San Diego Air & Space Museum.

Works

More photos

• book

  • Applied Hydro and Aeromechanics

    (Based on the famous series of lectures given at Göttingen...)

    1934
  • Essentials of Fluid Dynamics: With Applications to Hydraulics, Aeronautics, Meteorology and Other Subjects 1952
  • Führer durch die Strömungslehre 1931
  • Fuhrer Durch Die Stromungslehre 1941
  • Die physikalischen Institute der Universitat Gottingen 1906
  • Die Grundlehren der technischen Mechanik: Mit specieller Berücksichtigung 1897
  • Essentials of Fluid Dynamics with Application to Hydraulics, Aeronautics, Meteorology and Other Subjects 1953

Religion

Ludwig was baptised when he was exactly one week old.

Politics

Prandtl appears to have happily served as an ambassador for the Nazi regime, writing in 1937 to a NACA representative "I believe that Fascism in Italy and National Socialism in Germany represent very good beginnings of new thinking and economics." Prandtl's support for the regime is apparent in his letters to G. I. Taylor and his wife in 1938 and 1939. Referring to Nazi Germany's treatment of Jews, Prandtl wrote: "The struggle, which Germany, unfortunately, had to fight against the Jews, was necessary for its self-preservation." Prandtl also claimed that "If there will be war, the guilt to have caused it by political measures is this time unequivocally on the side of England.

Membership

Prandtl was elected to the Royal Society of London in 1928.

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  Royal Society of London , United Kingdom

  1928 - 1953

Personality

Prandtl’s personality was distinguished by the inclination to absorb himself totally in what interested him. The details of toys and magic tricks fascinated him to the exclusion of his surroundings. His greatness as a teacher did not include greatness as a lecturer because “he could not make a statement without qualifying it” and consequently was tedious.

Nevertheless, Prandtl was personable, gracious, and unassuming. He was an accomplished pianist with a good musical sense. His importance as a researcher was matched by an extraordinary ability to work fruitfully with his individual students.

Quotes from others about the person

• Von Karman: "Prandtl, an engineer by training, was endowed with a rare vision for the understanding of physical phenomena and unusual ability in putting them into relatively simple mathematical form. His control of the mathematical methods and tricks was limited; many of his collaborators and followers surpassed him in solving difficult mathematical problems. But his ability to establish systems of simplified equations which expressed the essential physical relations and dropped the nonessentials was unique, I believe, even when compared with his great predecessors in the field of mechanics – men like Leonhard Euler and d’Alembert."

Connections

In his autobiography, Kármán gives a picture of Prandtl that clearly mingles affection with annoyance. Prandtl’s life was, he tells us, “particularly full of overtones of naïveté.” In 1909, for example, Prandtl decided he really ought to marry; but he didn’t know how to proceed. Finally, he wrote to Mrs. Föppl, asking for the hand of one of her daughters. But which one? Prandtl had not specified. At a family conference, the Föppls made the practical decision that he should marry their eldest daughter, Gertrude.

On 11 September 1909, Prandtl married Gertrud Föppl in Munich. They had two daughters, Hildegard born in 1914, and Johanna born in 1917.

Father:

Alexander Prandtl

1840-1896, Prandtl's father Alexander was a Professor at the Agricultural College Weihenstephan in Freising. He carried out research on milk production and wrote scientific papers such as On the theoretically expected effect of creaming caused by centrifugal forces (1877) and The effect of currents caused by heating or cooling milk (1879).

Mother:

Magdalena Ostermann

colleague:

Michael Max Munk

Max Michael Munk (October 22, 1890 – June 3, 1986) was a German aerospace engineer who worked for the National Advisory Committee for Aeronautics (NACA) in the 1920s and made contributions to the design of airfoils.

Wife:

Gertrud Föppl

Daughter:

Hildegard Prandtl

born 1914

Daughter:

Johanna Prandtl

born 1917

collaborator:

Richard von Mises

In 1922 Prandtl, together with Richard von Mises, founded the GAMM (the International Association of Applied Mathematics and Mechanics) and was its chairman from 1922 until 1933.

Grandfather:

Antonin Prandtl

grandmother:

Anna Charlotte, nee Hauttmann

teacher:

August Foppl

mentor:

Felix Klein

colleague:

Theodore von Karman

colleague:

Theodore von Kármán

1881 - 1963, von Kármán was a Hungarian born mathematician, aerospace engineer, and physicist who worked in the fields of aeronautics and astronautics. He is responsible for many key advances in aerodynamics, notably his work on supersonic and hypersonic airflow characterization. He is regarded as the outstanding aerodynamic theoretician of the 20th century.

colleague:

Albert Betz

Albert Betz (25 December 1885 – 16 April 1968) was a German physicist and a pioneer of wind turbine technology. Prandtl worked with Albert Betz and Max Munk on the problem of a useful mathematical tool for examining lift from "real world" wings.

Friend:

Geoffrey Ingram Taylor

Sir Geoffrey Ingram Taylor, March 1886 – 27 June 1975, was a British physicist and mathematician, and a major figure in fluid dynamics and wave theory.

Friend:

Karl Schwarzschild

References

• Elements of Gasdynamics
  2002
• The Wind and Beyond: Theodore von Karman, Pioneer in Aviation and Pathfinder in Space
  1967
• Serving the Reich: The Struggle for the Soul of Physics under Hitler
  2014
• Scientists under Hitler: Politics and the Physics Community in the Third Reich
  2018
• Ludwig Prandtl: A Life for Fluid Mechanics and Aeronautical Research
  2019
• Ludwig Prandtl – Strömungsforscher und Wissenschaftsmanager: Ein unverstellter Blick auf sein Leben
  2016