Hans W. Liepmann
1914 – 2009

Hans Wolfgang Liepmann, a pioneering researcher and passionate educator in fluid mechanics, passed away on June 24 at his home in La Cañada Flintridge. He was 94.

Liepmann, the Theodore von Kármán Professor of Aeronautics, Emeritus, came to Caltech in 1939 and was the third director of Caltech's Graduate Aeronautical Laboratories (GALCIT), from 1972 to 1985.

Known for his sharp wit and distinctive accent, Liepmann was a noted teacher who mentored more than 60 PhD students and hundreds of undergraduates during his career at GALCIT.

He was born in Berlin in 1914. His father, a well-known physician and hospital director, decided to emigrate following the rise of the Nazi government and the infamous Reichstag fire in 1933. Liepmann joined his family in Turkey in 1934 after his father was invited to be head of the gynecology department at the University of Istanbul. He later studied in the physics department at the University of Zürich, and pursued his doctoral studies on low-temperature physics under Richard Bar.

Liepmann came to the U.S. in 1939 after impulsively expressing an interest in "hydrodynamics" during a drinking party at his PhD defense. An offer from Theodore von Kármán led to a research position in experimental fluid mechanics at GALCIT, where Kármán was the first director. Liepmann studied boundary layer instability, transition to turbulence, and various turbulent flows. With the entry of the U.S. into World War II, he began research on problems associated with high-speed flight, including transonic flight phenomena and interaction of shock waves with boundary layers on aerodynamic surfaces.

By 1949 he had advanced to professor of aeronautics at Caltech and had developed a vigorous program of research. A strong believer in the importance of teaching, he was instrumental in Caltech's introduction of the applied mathematics option in 1967 and the applied physics option in 1974. Throughout his career, up to retirement, Liepmann was devoted to teaching both graduate and undergraduate courses. The enthusiasm, clarity, and teaching effectiveness of his lectures are legendary.

Liepmann was elected a member of the National Academy of Engineering and the National Academy of Sciences. He was a recipient of the National Medal of Technology and the Ludwig Prandtl Ring—the highest honor conferred by the German Society for Aeronautics and Astronautics. In 1986, President Ronald Reagan awarded him the National Medal of Science.

Liepmann leaves behind sons Dorian, Till, Christopher, and Paul, and two grandchildren. His wife, Dietlind, passed away in 1990.

A memorial service for Liepmann is scheduled for January 23, at 2:00 p.m. at the Athenaeum. —JW