I came to Emmanuel in 1984 to read Mathematics, and have been here in various guises ever since.
After three years as an undergraduate I took Part III Mathematics (a one-year Masters course, now taken by about 100 Cambridge students who are joined by about 150 students from elsewhere, many from overseas). I knew by this time that I was more inclined towards applied mathematics than pure mathematics, but the subject which particularly interested me was the mathematical theory of waves. Of course waves are ubiquitous, and wave theory plays a key part in a vast range of scientific disciplines and technologies, from meteorology to mobile communications. But the application which I worked on for my PhD, and have worked on ever since, is aeroacoustics, which is the science of the generation and propagation of sound in air. In terms of its application, aeroacoustics is most identified with aviation, but clearly noise pollution is not the sole preserve of aircraft, and the noise from large onshore wind farms is a source of growing controversy. (more on that in a moment).
In the late 1980s the big new thing in aviation was the Propfan, a large twin propeller , one placed behind the other and rotating in opposite directions. The Propfan is significantly more fuel efficient than the conventional turbofan which powers almost all passenger aircraft, but it does have some noise issues. The aim of my Phd was to predict, for Rolls-Royce who were developing a version of the Propfan at the time, the engine noise heard in the cabin, and I duly completed this task in 1991. However, the relatively low price of aviation fuel at the time meant that there was not enough commercial incentive to manufacture the Propfan, and the project was shelved in the very early 1990s. This was not a complete disaster for me personally, because what I had learnt from working on the Propfan readily carried over to acoustic prediction for the more conventional aeroengines, and this has been a theme of my research ever since. Interestingly, the Propfan project has been revived (but now with a different name, the Counter –Rotating Open Rotor) , not with the aim of reducing fuel consumption to save money but now as a way of significantly reducing the carbon footprint of air travel. I think there is a very good chance that we’ll be seeing these new engines on many aircraft in the next 5-10 years.
As already mentioned, mathematical wave theory can be used to describe a wide range of phenomena, and as well as working on aircraft noise I have been fortunate enough to be involved in several other research projects, including the way that polar sea ice breaks up because of the action of ocean waves, why it is that aircraft vapour trails hang around so long in the sky, and even on one occasion on how vibrations from a cruise ship propeller could be reduced so as to improve the dining experience of the paying passengers! However, one project which I am involved with at the moment really stands out in my mind, and that is the question of what we can learn from owls about how to make wind turbines quieter!
So how does an owl help with aeroacoustics? The point is that many owls can hunt in acoustic stealth, producing much less noise than you might expect in the audible frequency range of their prey (to avoid detection) and in their own audible frequency range (so that they can hear their prey in the first place). This is achieved, we think, by two features which are not found on any other bird; first, the feathers on the upper wing surface have an exceedingly complicated microstructure, with layers of interleaved barbs and hairs; and second, the wing trailing edge possesses a small flexible and semi-porous fringe. It turns out that the trailing edge is the part of the wing (for either a bird or a plane!) which produces the most noise (a fact proved by a former Master of Emmanuel College, Shon Ffowcs Wiliams). The role of the trailing-edge fringe is therefore clear, and we have been able to demonstrate mathematically that having a flexible and porous trailing edge is indeed a very good way of suppressing trailing-edge noise. The role of the feather microstructure is less clear, but engineers at Viginia Tech in the US are conducting experiments (not on real owls!) which we hope will give us some clues about how to build a suitable mathematical model. The eventual dream is to design a special surface treatment which could be used to make wind turbines much quieter.
As much as I enjoy doing research, one of the great privileges of academic life is having the opportunity to teach so many brilliant and interesting students, and I derive great pleasure and satisfaction from giving lectures in the University and from supervising Emmanuel undergraduates in mathematics. I think of myself as being tremendously fortunate to be part of such an exciting and vibrant community.