Professor Geoffrey Michael Lilley passed away on 20 September at the age of 95. His wonderful wit, his colourful stories, his sense of humour, and his insightful intellect will be missed by all those who had the privilege of knowing him.
Professor Lilley was born on 16 November 1919 in Isleworth, Middlesex, just a few miles east of the present-day location of Heathrow Airport. He attended Isleworth Grammar School, but left at the age of 15 to join the RAF with dreams of flying. Unfortunately his poor eyesight ruled this out, so in 1934 he resigned and became a general engineering apprentice and, in 1938, the assistant to the Chief Engineer of Kodak (Wealdstone). Having left school early, he had no formal technical training, so he increased his knowledge by taking evening classes and from private study. As a measure of his abilities he was able to design the air-conditioning system for Kodak’s new film cooling and drying plant. It became operational in June 1939 and operated throughout WW2. This provided the Air Ministry with all the film they required for air reconnaissance during the War.

In 1940, Professor Lilley joined Vickers Armstrong in Weybridge and Vickers Supermarine in Southampton. He was assistant to George Edwards and Dr Barnes Wallis and worked on numerous aircraft and high speed bomb projects. He continued his studies at evening classes and received his Higher National Certificate with Distinction and his BSc(Eng.) with first class honours in 1940. Sir George Edwards allowed Professor Lilley to take two mornings a week away from work to attend postgraduate classes at Imperial College to study for the MSc(Eng) and DIC (Diploma of Imperial College), which he received in 1945. The hours he lost at work had to be made up by working evenings and weekends. His Master’s thesis was devoted to nozzle design at subsonic and supersonic speeds using the Chaplygin theory of compressible flow. At the same time, during WW2, Professor Lilley served for two nights a week with a Home Guard Anti-Aircraft battery defending London.

At the end of the War in 1945, Professor Lilley was charged with designing commercial subsonic and supersonic wind tunnels. Before he left Vickers Armstrong he had completed all the working drawings for the 13 x 9 foot low-speed wind tunnel. This same tunnel is operating today at British Aerospace Systems (Wharton). He also designed similar low-speed tunnels for English Electric and Vickers Supermarine and smaller versions for universities.

In 1946 Professor Lilley was appointed as a founder academic of the postgraduate College of Aeronautics at Cranfield. There, he designed the Aerodynamics Laboratory, which included subsonic, transonic, supersonic and hypersonic wind tunnels. In 1961 he was appointed Professor of Experimental Fluid Mechanics. In 1948 Professor Lilley began research into jet noise and its reduction. Research into the reduction of jet noise and the theory of sound generation by turbulence continued throughout his career. His work with A D Young and R Westley resulted in the design and patent of the corrugated noise reduction nozzles fitted to all civilian jet aircraft from 1959 to 1970. Derivatives of these devices are still fitted to all commercial aircraft flying today. In 1952, Professor Lilley presented his work with Westley at the eighth International Congress of Applied Mechanics in Istanbul, Turkey. In an appendix to that paper, he described a physical theory of noise generation based on fluctuations in the rate of energy transfer from the large eddies in the jet mixing region into smaller eddies. Following heated discussions with Lighthill, who was in the process of publishing his own theory of aerodynamic noise, Professor Lilley discontinued work on this aspect of jet noise theory. More than 50 years later, at the age of 89, he returned to this theory, which was published in The Aeronautical Journal.

In 1953, working with Westley, Yates and Busing, Professor Lilley developed the first definitive study of the ‘supersonic bang’ and the pattern of shock waves around an aircraft flying at both steady supersonic speeds as well as accelerated and decelerated flight. The associated experimental work used a hydraulic analogy wave tank with aircraft models in both steady and accelerated flight. These results, which Professor Lilley and his co-workers interpreted would describe shock patterns around aircraft at sonic and supersonic speeds, were later interpreted by astrophysicists to represent stars and galaxies in accelerated motion close to the speed of light.

Beginning in 1956, Professor Lilley was a member of the Supersonic Transport Aircraft Committee (STAC). This committee was established by the Ministry of Supply to initiate exploratory research into economic supersonic transports. The committee laid the foundations for Concorde. To improve low-speed performance and control as well as improved aerodynamic efficiency in cruise at Mach 2, Professor Lilley started work on leading edge blowing on a low aspect ratio delta wing. This work resulted in shared patents with Küchemann and Maskell from the Aerodynamics Department at the Royal Aircraft Establishment at Farnborough.

In 1955, during one of his many visits to the United States to discuss aircraft noise reduction, Professor Lilley was involved in a serious car accident and suffered head injuries, memory loss and epilepsy. Fortunately he recovered fully in just under two years and was able to return to his work on the theory of jet noise and to applications of Lighthill’s theory for the prediction of jet noise.

Professor Lilley served for many years as chairman of the Noise Research Committee of the Aeronautical Research Council. He later became chairman of the Noise Advisory Council’s working party on the noise from air traffic. Following lengthy arguments between Professor Lilley, representing the views of the ARC’s Noise Research Committee, and the Government, on the difficulty of meeting the proposed noise limits for the Concorde at take-off, agreement was reached with Sir Stanley Hooker of Rolls-Royce in 1965 to set up a Jet Noise Panel between Rolls-Royce and SNECMA to bring in external expertise to advise on how the noise problems could be solved. No satisfactory short term solutions to reduce the Concorde’s engine noise were found. However, it was demonstrated by British Aerospace and Rolls-Royce, through changes in Concorde’s flight trajectory and the introduction of cutback, that the perceived noise levels at monitoring positions in the nearest residential communities would not exceed the noise of all other commercial aircraft. Professor Lilley had the responsibility to negotiate with the New York Port Authority that the Concorde could meet 110PNdB at the noise monitoring points at New York’s Kennedy Airport, the requirement for all other commercial aircraft, forcing the Port Authority to lift the ban on Concorde’s flights to the USA. This was an achievement of which Professor Lilley was particularly proud.

In 1963, Professor Lilley was appointed to the Chair of Aerodynamics and Astronautics at the University of Southampton. This chair was held previously by Professor Elfyn Richards who had established the Institute of Sound and Vibration Research (ISVR). Professor Lilley promoted strong links with the ISVR as well as the Mathematics Department at Southampton, which had a very strong fluid mechanics group including Curle, Thwaites, Davies, and Holstein. He also continued his long relationship with the Royal Aircraft Establishments at Bedford and Farnborough. Professor Lilley set up an Industrial Research Unit to perform research and development work for industry using the Department facilities. In conjunction with Professor Thwaites of the Department of Mathematics he established the Theoretical Aerodynamics Group charged with the introduction of large-scale computing in fluid dynamics in the UK.

In 1970, Professor Lilley became a consultant to the Lockheed-Georgia Company in Marietta, Georgia. Harry Plumblee, who had pursued his PhD in the ISVR, had organised the research team. Among the other consultants from Southampton were Phil Doak, Chris Morfey, and Mike Fisher. Volume IV of the technical report to the sponsors (the Air Force Aero Propulsion Laboratory and the Department of Transportation) was entitled “Theory of Turbulence Generated Jet Noise. Noise Radiation from Upstream Sources, and Combustion Noise.” Professor Lilley contributed the chapter on the ‘Generation of Sound in Mixing Regions’. This work contains the derivation of what is now known as ‘Lilley’s Equation’. It is a third order convected wave equation that includes the effects of the propagation of sound through the mean flow from sound sources in a mixing layer or jet. It also includes explicit forms for the source terms themselves, which he showed to be at least second order in the turbulent fluctuations for a unidirectional mean flow. When Harry Plumblee expanded the research team in Georgia, I was lucky enough to join with the other new team members from Southampton, including Brian Tester, Himat (Bob) Tanna, Peter Dean, and Jark Lau. Talented employees already at Lockheed-Georgia, in addition to Harry Plumblee, were Bob Burrin and Clay Whiffen - two exceptionally talented experimentalists and instrumentation experts. The experimental and analytical work that was produced by the team is still referenced today.

Professor Lilley retired from his University Chair in 1983 and became Professor Emeritus. However, his academic activities and research did not finish with his retirement. From 1980-89 he was a part-time visiting professor at the Middle East Technical University in Ankara. There he helped to establish the new Department of Aeronautical (now Aerospace) Engineering. In 1985, Professor Lilley was invited by his friend and colleague, Shen Yuan to visit the Beijing Institute of Aeronautics. Professors Yuan and Lilley had been fellow students of Professor Bairstow at Imperial College. Professor Lilley had been working on internal aerodynamic solutions to the Chaplygin equations, whereas Professor Yuan had conducted research in external aerodynamics and had received his PhD after three years work. Professor Lilley was awarded the MSc(Eng) for his two years of part-time study. In 1989-90 Professor Lilley was a visiting professor at the University of the Witwatersrand, Johannesburg, South Africa. This was at the same time that Nelson Mandela was released from prison in February 1990.

In 1991, Professor Lilley joined the Institute for Computer Applications in Science and Engineering (ICASE) at the NASA Langley Research Center in Hampton, Virginia. He became the Chief Scientist in 1998. He worked on assessing the viability of computational approaches to aeroacoustics. This included visits to Stanford University to collaborate with many researchers, including Professors Parviz Moin and Sanjiva Lele, on the Direct Numerical Simulation (DNS) of aerodynamic noise.

Professor Lilley had a long time interest in the silent flight of the owl and how this natural ability could be used to reduce the noise of commercial aircraft on the approach to major airports. Professor Lilley has pioneered the concept of a ‘no-fly zone’ below 1km altitude and 1-2km from the airport boundary, so that all aircraft would not be heard above the background noise surrounding the airport. His research included the noise of landing gear and, with support from NASA Langley, Professor Lilley worked with researchers at Langley and Penn State on the development of design-oriented models for landing gear noise. In view of his close connection with the faculty and students at Penn State, Professor Lilley was appointed Adjunct Professor of Aerospace Engineering at Penn State in 2001.

Professor Lilley had always loved cars from his Alvis to his Alfa Romeo Spider. Many colleagues and students had the experience of a lifetime as passengers. Some declined a second opportunity to ride with him. In 1953, Professor Lilley, with the assistance of Ken Ross, had generated the aerodynamic design, from wind-tunnel tests using the ground board reflection technique, of the ‘Arnott Streamliner’. On 28 October 1953, the car, driven by John K B Brise, set nine new world speed records in the 500cc engine class at L’autodrome de Linas-Montlhéry to the south of Paris. His interest in cars also led him to encourage the development of a moving ground in the Southampton Aero Department low speed wind tunnel. Later Professor Lilley was able to obtain the 9x7 foot tunnel from the Royal Aircraft Establishment that had become surplus to their needs. The successful operation of the 9x7 foot tunnel led to an explosion of interest among the Grand Prix racing teams. The School of Engineering Sciences at Southampton University now offers an MSc degree in Race Car Aerodynamics.

Professor Lilley has been recognised with numerous awards. In 1981, he was awarded the Order of the British Empire (OBE) for ‘Services to Government’. In 1983, he was awarded the Gold Medal of the Royal Aeronautical Society and, in the same year, he received the Aeroacoustics Award from the American Institute of Aeronautics and Astronautics (AIAA), “For major contributions to aeroacoustics research, including sonic boom and jet noise, and particularly for his theory of the generation and radiation of sound by turbulence and the practical suppression of jet noise.” He was a Fellow of both the AIAA and the Royal Aeronautical Society. In 2004, Professor Lilley was awarded an honorary Doctor of Science degree by the University of Southampton.

Professor Lilley was never reluctant to take on controversial issues. He fought strongly against the proposed route for the M27 motorway. Unfortunately, this was not a successful fight. He was a strong advocate for any student who was not being treated fairly by the authorities, even one time acting as a McKenzie Friend for a foreign student.

There are no awards available for great story tellers. If there were, Professor Lilley would certainly be a recipient. Ever since I knew him, and almost certainly before, each of his international trips would result in some kind of incident, usually involving people in authority. On a trip to Russia he gave his escort Natasha the slip and was able to deliver information on the Russian version of Concorde to the British Embassy. On a trip to China, he made the mistake of giving his host an electronic chess set. This resulted in him being detained at the exit point and having to pay fines to be allowed to leave the country. Once, he found himself in the middle of a demilitarised zone in Israel when he was out for a walk. On a visit to South Africa he was involved in a knife fight but was able to defend himself. These stories would usually be told after dinner. Sometimes the stories would be repeated. It was very clear on many occasions that his wife ‘Peggy’ had heard them more than once, as she would drift slowly and comfortably off to sleep during the telling.

Professor Lilley was preceded in death by his wife Peggy and is survived by three children, Grete, Lisa and Michael, grandchildren and great grandchildren.

Professor Philip J Morris

28 October 2015