Professor George Keith Bachelor FRS, 1920-2000

Julian Hunt

jcrh@mssl.ac.uk

Without George Batchelor modern fluid mechanics would not be the discipline it is today; which he saw as combining physical insight and the application of mathematics directed towards the solution of specific problems; a philosophy of science that was, he said, epitomised by H. Poincare's Science and Method. Batchelor ensured that his vision of the subject and his high standards prevailed both by the example of his own brilliant research work and thorough exposition, (in an unusual prose style that somewhat reflected his admiration for that of Henry James), and by his forceful, tenacious and inspired leadership of Cambridge and internationally based institutions most notably the Journal of Fluid Mechanics whose world-wide circulation peaked at about 2500 per issue.

Batchelor was an exceptional schoolboy, who entered Melbourne University to read both mathematics and physics at the age of 17. He excelled and on graduating in 1940 joined the Aeronautical Research Laboratory to work during the war on fluid flow problems in aircraft engines. Many years later his junior colleagues at Cambridge could still consult him about engineering problems, many of which he had tackled before, but like Archimedes had not bothered to write up these practical application of science. This experience only whetted his appetite for fundamental study of fluid mechanics which he began in 1945 in Cambridge arriving by ship with his newly married wife Wilma (nee Raetz). He came to work on turbulence under Sir Geoffrey Ingram Taylor who had laid the foundations for its quantitative theory in the 1930's, but who was no longer interested in the subject. Indeed when Batchelor, having discovered in the Scientific Periodicals Library the issues of the Russian Academy of Sciences reporting A.N. Kolmogorov's 1941 seminal theory for the structure of small scale turbulence, excitedly told Taylor, he was rebuffed with the comment that it all rather obvious - perhaps only to Taylor!

Not put off, Batchelor wrote up his masterly interpretation of the theory in 1947. Until then, as Kolmogorov's own students used to say, the Russian themselves did not really understand this great break through. In Batchelor's own contributions to turbulence research he greatly extended and applied the statistical and geometrical theories of Taylor and von Karman and the physical 'scaling' arguments of Kolmogorov and Obukhov. He is chiefly remembered for his work on the laws governing large eddy motion and small scale temperature fluctuations in turbulence, on the dispersion of smoke plumes in a turbulent atmosphere, and on how turbulence can be rapidly amplified or damped whether in the turbulence, or in cosmic gas clouds. His book on Homogeneous Turbulence in 1953, which won him the Adams Prize is still a basic guide to the subject. With his Australian colleague Alan Townsend and a stream of excellent research students from all over the Commonwealth they established the Cambridge School of Turbulence; there were many joint papers and lectures in alternate years by Batchelor and Townsend.

During the 1950's; as a Fellow of Trinity College, and University Reader he established in pokey offices in the Cavendish Laboratory in Free School a world famous group of fluid dynamics, under the benevolent eye of G.I. Taylor, who was still, in his 70's, doing his experiments and asking question about everyone else's. At the formidable seminars held at 4.30 on Fridays, which Batchelor instituted in 1948, many crucial theoretical developments were first presented including his own. He managed these lively occasions like a circus lion tamer, with a turn of his head and a stare at any stupidity or excessive harassment of visiting speakers.

To report on the rapid and exciting developments in the subject, many of which resulted from the cold-war boom in aerospace, Batchelor saw that a new journal was needed, which he founded in 1956 as the Journal of Fluid Mechanics. He readily persuaded the leading specialists from over the world to join the Editorial Board; one of the greatest honours for a fluid dynamicist is still to be invited to be an Associate Editor of JFM!

When Batchelor wrote about the journal in the special 25th anniversary in 1981 he was evidently proud of its exacting standards, but he also revealed other motivations, notably his belief in J.D. Bernal's social function of science. It is no accident that with leaders like Batchelor university mathematics continues to flourish in the UK where, unlike in many other countries, mathematical graduates are welcomed by employers because of their knowledge of how mathematics is applied in practice and in computation. In the late 1960; with sponsorship from Shell his department was the first to introduce computation into the regular mathematics courses.

Batchelor applied his mathematics to the design of his house which he was building in Conduit Head Road, (financed, he said, by giving seminars in the USA!). After analysing the air movement between double glazing panes (on which he wrote a well known paper in 1954) he calculated that an unusually large 3cm gap is the optimum; this ensured an Australian shirtsleeve indoor temperature and also minimised cleaning problems for Wilma by reducing dust accumulation caused by unnecessary variations in temperature.

They brought up three daughters in the house which was a great centre of warmth and happiness to lots of visitors, including small children at the annual departmental party. Wilma also worked voluntarily and with great energy on many welfare and housing projects for those suffering from poor mental health in Cambridge; she was awarded an MBE .

Batchelor's determination and meticulous planning were equally needed in his long task of first setting up and then developing the Department of Applied Mathematics and Theoretical Physics at a time (in the 1950's), when no departments at Cambridge existed in mathematics (or most other non-experimental subjects). He had to win many close votes at departmental and University committee meetings; he regularly faced hostility in periods of financial stringency from the departments of Physics and Engineering who said that the expenditure on experiments in a mathematics department was unnecessary. The battles he won have benefited mathematics departments all over the world where it is now unremarked to have such facilities. It was sometimes a breath-taking experience to see how groups around a table were seen off at these meetings, and how he lived to fight another day. Not surprisingly his success did not always endear him to everyone in Cambridge or indeed in the UK. The informal Australian Batchelor was best seen either talking to women with whom he enjoyed talking about his great interests in deserts and gardens, or far from Cambridge, in an open neck shirt at conferences; he wore a pink one on the platform in the Kremlin at the International Congress of Theoretical and Applied Mechanics was held there in 1972; he enjoyed visiting his friends in flats in the old centre of Warsaw. When he returned to London airport he teasingly replied to the immigration questions about the expected duration of his stay in the UK 'life', 20 years etc; he never gave up his Australian passport.

His great belief in European collaboration, especially between east and west, inspired his chairmanship for nearly twenty years of the European Mechanics Committee. He stimulated an outstanding programme of colloquia covering all the new aspects of solid and fluid solid mechanics, such as magnetohydrodynamics and later environmental problems and non-linear systems; they were often the envy of our US friends. He was honoured by universities and academies all over Europe and the US, though not by other Universities in the UK. He was fittingly awarded the Royal Medal for his research by the Royal Society in 1988.

After he reached 40 he decided that there was no more research he could do in turbulence, so he first turned to writing 'An Introduction to Fluid Dynamics '(1967), still the most complete text book for mathematically inclined students and researchers from all over the world. It has had many translations and been so successful financially that from its proceeds Batchelor funded scholarships at Cambridge and Melbourne Universities. Secondly in the 1960's he began a new line of research, on the statistical distribution of small particles and bubbles as they settle and disperse in liquids and gases; using some of the same techniques he had developed in his turbulence research his analysis took the next step beyond Einstein's calculations in 1906 to account for the mutual interactions of the particles. His new approach led to the formation of another 'school' with new students and researchers coming to work with him on problems of chemical engineering and rain in clouds. During this period he actively encouraged the application of research to industry, through working with the new companies coming to Cambridge, and pushing hard with like minded colleagues to help Cambridge University to establish its industry-friendly approach. His final projects were to organise a major conference in 1986 on fluid mechanics in the spirit of G.I.Taylor, and to write a scientific and personal biography of his great supervisor. His aim as always was didactic; to show students how fluid mechanics should be done!

Batchelor's portrait by Rupert Shephard hangs in the department he founded; it shows him in his favourite fawn summer jacket doing vortex doodles on a pad and giving us half a smile; it took the artist 14 sittings to get that much from quite a complex man.

Sadly he suffered from Parkinson's disease after his wife Wilma died in 1997. He moved into Trinity College where colleagues and friends from everywhere visited and telephoned him, until he moved to a nursing home in early March 2000.