Obituary: Philip Saffman

Born Leeds, March 19, 1931.
Died Pasadena, California, August 17, 2008, aged 77.

A world expert on patterns of fluid movement, especially rotation or eddies, Professor Philip Saffman used his skill in applied mathematics and aeronautics to solve and avoid certain types of air crash, writes John Fisher.

The son of Sarah and Sam Saffman, a well-known Leeds solicitor, he broke the family mould by not joining the family firm, unlike his two brothers, one of whom survives him.

Educated at Roundhay, Leeds' premier grammar school, Philip shone academically, gaining honours in some 10 subjects in Higher School Certificate, the equivalent of today's A-Levels, when he was just 15.
His fascination with water emerged while on family holidays. He would sit on the beach for hours observing the movement of the waves.

At 16 he took a gap year and went to stay with relatives in Baltimore, returning to England to do his national service. A year later the RAF released him as "something of a prodigy". He entered Trinity College, Cambridge, where he gained his bachelor, master and doctoral degrees.

In 1954, he married Ruth Arion, sister of a former classmate at Roundhay. In 1958 he was appointed assistant lecturer in applied mathematics at Cambridge and the couple moved to the city.
After teaching the subject at Cambridge and at King's College, London, for six years, he moved in 1964 to the US as professor of fluid mechanics in the division of engineering and applied science at the California Institute of Technology, better known as Caltech.

Professor Saffman made his name with his study on what occurs when a fluid of low viscosity, such as water, is injected into a fluid of higher viscosity, or stickiness, such as glycerine. The behaviour he observed and described became known as the Saffman-Taylor instability, and is closely related to many technologically important processes, such as flow in a porous medium.

His research into the subject was instrumental in helping oil companies to develop the best methods of recovering trapped oil by injecting water or steam to force the oil to the surface.

He also made fundamental contributions to the understanding of vorticity, the way ships move through water and aircraft through air.

His meticulous mathematical analysis of turbulence in the wake of jet aircraft during take-off allowed him to calculate how long it takes for turbulence to disperse. This determines when it is safe for another aircraft to follow.

Acting as consultant following several aircraft disasters, he helped explain the conditions that contributed to the accidents. One of these was the 1985 Dallas air crash involving a Delta Air Lines flight which tried to land in a thunderstorm, killing 135 people.

Investigation revealed that the weather had changed drastically in the eight minutes prior to the crash. Professor Saffman helped persuade air-traffic controllers to allow a minimum period between take-offs, to allow turbulence to subside in the wake of preceding aircraft.

Elected a fellow of the Royal Society in 1988, Professor Saffman was also a fellow of the American Academy of Arts and Sciences and was awarded the Otto Laporte Award by the American Physical Society.
Author of numerous papers in scientific journals, he was co-author of Vortex Dynamics (1992), analysing a field in which he became a principal contributor.

In 1995 he was named the Theodore von Kármán Professor of Applied Mathematics and Aeronautics at Caltech.

He spent his retirement years from 2001 quietly with his family until his long final illness. A gentle, soft-spoken man with a dry sense of humour, he kept a low profile and refused to comment on what he did not understand.

He was a first-rate scientist and inspiring teacher with the rare ability to explain complicated results in a simple way which always reached the heart of the matter.

Colleagues at Caltech paid tribute to his generosity as mentor and friend to many, and praised his unwavering commitment to the highest standards of scientific excellence and integrity in every aspect of his work.

He is survived by his wife, Ruth; three children, Louise, Mark and Emma; and eight grandchildren.