In many practical circumstances in aeronautical engineering and in related industries, flows arise where concentrated streamwise vorticity is embedded within a turbulent shear flow. The juxtaposition of these features makes such flows particularly challenging to compute using CFD methods. In particular, one may be forced to abandon strategies for modelling the turbulent stresses that prove adequate in two dimensional shear flows (i.e. in flows where the vorticity vector is orthogonal to the mean velocity). The paper reviews developments in modelling turbulent stresses from their transport equations (rather than by appeal to an eddy viscosity hypothesis) and demonstrates, by way of a range of examples, the capabilities of this approach for handling flows with concentrated streamwise vorticity.

It is indeed a great honour and a particularly pleasing experience for me to have been invited to give the 18th Lanchester Memorial Lecture. Pleasing because it enables me to recall before such a distinguished audience, one of Lanchester's outstanding achievements in the field of aircraft stability, his phugoid theory. This slow oscillation problem has often been neglected but its implications can be vital as the Vulcan crash in 1956 emphasises, and the development of STOL with high lift has forced designers to turn again to a serious consideration of the phugoid as I will show presently in the first part of this lecture.

The problem of air-breathing engines capable of flying at very high Mach numbers is described briefly. Possible performance of supersonic combustion ramjets is outlined briefly and the supersonic combustion process is described. Two mechanisms of combustion are outlined: one is supersonic combustion controlled by convection process, and the second is controlled by diffusion. The parameters related to the combustion process are discussed in detail. Data and analyses of reaction rates and mixing phenomena are represented; the flame mechanism is discussed, and experimental results are presented.

I am very appreciative of the honour that has been accorded me in being invited to deliver the Second Lanchester Memorial Lecture: appreciative, but all too conscious of my own inadequacy. This is especially true, since in the first Lecture we heard a tribute to a very great man from another such: and the prospect of following von Karman to this lectern is one to deter perhaps all but the most foolhardy. Since von Karman’s address discussed very fully the contributions of Lanchester to aeronautics, little is left for subsequent lecturers on this subject, and I have therefore chosen to speak of a problem which has been my special interest and concern throughout my professional life, namely, aeroelasticity—a field in which, as in so many others, Lanchester was a pioneer.

One of the early triumphs of the Lanchester-Prandtl wing theory was that it explained the effects of wind tunnel boundaries and provided explicit and simple formulae to correct wind tunnel measurements for these effects. As every aerodynamicist knows, this theory tells us, with the help of “images”, that the boundaries, in the presence of a lifting wing, produce extraneous velocity components in the flow. At least two generations of experimenters have routinely corrected their angles of attack and their measured drag values for the presence of the vertical component.

Shockwaves are present in a flow as soon as the Mach number becomes supersonic. Being viscous phenomena, Shockwaves are a source of drag which can be predominant when the Mach number is significantly higher than one. In supersonic air intakes, the production of entropy by shocks is felt as a loss in efficiency. At high Mach numbers, Shockwaves produce a considerable temperature rise leading to severe heating problems, complicated by real gas effects. The intersection - or interference - of two shocks gives rise to complex wave patterns containing slip-lines and associated shear layers whose impingement on a nearby surface can cause detrimental pressure and heat transfer loads. The impact of a Shockwave on a boundary layer is the origin of strong viscous interactions which remain a limiting factor in the design of transonic wings, supersonic air intakes, propulsive nozzles and compressor cascades. More effort is needed to improve prediction of these interactions and to devise new techniques to control such phenomena.

Throughout his career, Lanchester’s phenomenal engineering output was directed mainly towards the automobile which proved in his day to be a more suitable vehicle than the aeroplane for the practical application of the products of his genius. Aeronautics remained always a compelling avocation “wholly individual … never backed by funds from external sources”, to quote his own words. During the First World War he did contribute to the practical solution of a serious tail flutter problem on Handley Page and de Havilland aircraft, making him probably one of the first applied aeroelasticians. However, his major contributions, cited in the 1931 award of the Guggenheim medal, were to the fundamental theory of aerodynamics. The full extent of these contributions is still being explored as Dr. J. P. Jones in the Thirteenth Lanchester Lecture points out. His contributions to automotive engineering, on the other hand, were immediately reduced to practice and it therefore seems appropriate in this Fourteenth Lanchester Lecture which it is my great privilege to present, to examine whether, as we continue the full exploitation of his discoveries in aeronautics, the aeroplane will ever be able to complement, possibly even replace to a degree, the ubiquitous automobile to whose practical realisation as a safe, comfortable and reliable transport medium he contributed so much.

Boundary layer theory is the cornerstone of our knowledge of the flow of air and other fluids of small viscosity under circumstances of interest in many engineering applications, especially also in aeronautics. Many complex problems in aerodynamics, as for instance the problem of skin friction, which was theoretically attacked very early by F. W. Lanchester, have been clarified by studying the flow within the boundary layer and its effects on the general flow around the body.

Research work on boundary layers, as started by Prandtl in 1904. was for the first twenty years—up to Prandtl's Wilbur Wright Memorial Lecture to the Royal Aeronautical Society in 1927—almost entirely restricted to Prandtl's Institute at Göttingen. But since about 1930 boundary layer theory has been generally accepted, and in the past thirty years there has been an almost exponential rise of the number of contributors to its further development.

The author tries to trace certain lines, along which this important branch of modern fluid dynamics has developed in the past thirty years. In this connection the following topics are treated to some extent:

1. I. Transition from laminar to turbulent flow.

2. II. Boundary layer control for high lift and low drag of aerofoils.

3. III. Aerodynamic heating at high speed (high Mach numbers).

4. IV. Boundary layer efff cts on swept wings and on rotating bodies.

I. The theoretical investigations of the problem of transition start from Reynolds' and Lord Rayleigh's hypothesis of the instability of laminar flow. After many unsuccessful attempts Tollmien, 1930, finally succeeded in calculating the critical Reynolds number for the boundary layer on a flat plate. More than ten years later Tollmien's stability theory was completely confirmed by very careful experiments of Dryden and his co-workers.

II. After many wind tunnel experiments the investigations of boundary layer control for high lift of aerofoils led to the construction of two aeroplanes with boundary layer suction at the aerodynamische versuchsanstalt gottingen, in 1938, which were quite successful. later on, also, a considerable reduction of the skin friction of aerofoils was obtained with the advent of the laminar flow aerofoil.

III. In flow at high Mach numbers the velocity boundary layer is accompanied by a thermal boundary layer which is caused by frictional heating. The large increase in the temperature of a solid surface in a high speed stream which can be calculated from boundary layer theory only, poses a serious problem to aeronautical engineers (“thermal barrier”).

IV. The aerodynamic characteristics of swept wings and Delta wings are largely governed by the behaviour of their boundary layer. Some of the draw-backs of such wing plan forms can be remedied by boundary layer control, as for instance by a “boundary layer fence.” For turbo-machines the influence of the centrifugal forces on the boundary layer plays an important role for their aerodynamic coefficients.

The Ninth Lanchester Memorial Lecture was given by Professor W. A. Mair, MA, FRAeS, on “STOL—Some Possibilities and Limitations” in the Society's Lecture Theatre on 12th May 1966. The Chair was taken by the President, Mr. A. D. Baxter, MEng, CEng, FRAeS. Before the lecture he presented the Society's Gold Medal for 1965 to Professor M. J. Lighthill, DSc, FRS, FRAeS, for “his outstanding original work in many fields of Aeronautics”, explaining that Professor Lighthill had been unable to be present at the Wilbur and Orville Wright Memorial Lecture in December 1965 when the Society's main awards for the year were presented.

The President then said that this was the first meeting of the Society since his installation as President and it was a very pleasant way to start his year in office with first, the presentation of the Gold Medal to one distinguished scientist and second, the introduction of another as the Lanchester Memorial Lecturer.

There would be many members of the Society who would remember Dr. Lanchester, his attendance at lectures and his contributions to the discussions. It was true, however, that the real stature of such men was rarely recognised at close quarters and often only in the light of later developments was the importance of their work realised. It was 20 years since Dr. Lanchester's death and their Memorial Lecture was in its ninth year. Each year, each President had added a tribute to this great man. He was a man of many parts—a scientist, musician, poet and engineer and aeronautics owed much to him. It was fitting that the Lecture had established a tradition of surveying some field of research associated with aerodynamics, in which Lanchester was so eminent. He thought that Lanchester would approve of both the subjects discussed and the distinguished men who had honoured his memory by presenting them. Before introducing Professor Mair he wished to welcome Mrs. Lanchester and Mr. George Lanchester and his wife, and Mrs. Mair.

Professor Mair must be well known to most of them. After graduating in Mechanical Sciences at Cambridge in 1939 he had joined the Royal Aircraft Establishment at Farnborough, where he scent some six years in the Aerodynamics Department doing research on high subsonic speed, both in the wind tunnels and in full-scale flight. In 1946 he had gone to the University of Manchester as Director of the Fluid Motion Laboratory and since 1952 he had held the Francis Mond Chair of Aeronautical Engineering at Cambridge. His chief interest there had been mainly in low speed aerodynamics and his authority in that field was widely recognised. In 1963 he had been appointed Chairman of the Powered Lift Committee of the Aeronautical Research Council.

The Sixth Lanchester Memorial Lecture, “Trends in Unsteady Aerodynamics,” was given by Dr. W. P. Jones, M.A., D.Sc., F.R.Ae.S., F.A.I.A.A., of the National Physical Laboratory, on 22nd November 1962. Professor A. R. Collar, M.A., D.Sc, F.R.Ae.S., F.A.I.A.A., F.C.A.S.I., President-Elect, took the Chair for the President who was visiting the overseas Divisions.

Before the lecture, Professor Collar introduced Dr. William Greulick, Scientific Attaché U.S. Embassy, who presented the John Scott Award to Mr. J. W. Sparke, R.A.E., for his invention of the Visual Glide Path Indicator, in use at most major airports of the world and adopted as the U.S. Standard. Dr. Greulick gave a short history of the Award, which was founded by John Scott, a chemist from Edinburgh, in 1816 and given to the City of Philadelphia. Its premiums were for distribution among “ingenious men and women who made useful inventions” and the award was of a truly international character. It was now of the value of $1,000, with a copper medal and a scroll.

Professor Collar, introducing the Lecturer, said that Lanchester had been a great scientist, a musician, a poet and an engineer of distinction in a great number of fields. It was to him a pleasure and a privilege to preside on this occasion, especially as he himself had delivered the second Lanchester Lecture. He was delighted that Professor Schlichting and Professor Young, two other Lecturers in the series, were present. Dr. von Kantian and Monsieur Legendre, the two other Lanchester lecturers, regretted that they could not be present.

The Sixth Lecturer, Dr. W. P. Jones, was Superintendent of the Aerodynamics Division of the National Physical Laboratory. He had been educated at St. David's College, Lampeter, and at The Quee's College, Oxford. He had joined the N.P.L. staff in 1935, where Professor Collar was himself working at the time, and had been at Teddington since then, except for a year (1960-61) when he was the Jerome C. Hunsaker Visiting Professor at Massachusetts Institute of Technology. Dr. Jones had written a large number of scientific papers on aerodynamic problems related to flutter and aeroelasticity and was the Editor of the AGARD “Manual on Aeroelasticity,” a volume of great substance and interest.

Ladies and gentlemen, it is an honour and a great pleasure to present this Lanchester Memorial Lecture. I thank the Royal Aeronautical Society and its Aerodynamic Committee for inviting me. In preparing this lecture I greatly enjoyed the added significance of presenting it in the historical context set by Lanchester. But the real pleasure is to be here among many good friends with whom I worked together for shorter or longer periods.

“A body that in its motion through a fluid does not give rise to a surface of discontinuity.” So Lanchester defined a ‘ streamline body’ in his standard work Aerodynamics. With ‘ discontinuity’ the boundary is meant between the outer flow and the dead water region formed by fluid that departs from the surface as illustrated nicely in Fig. 1 for the flow around a cylinder.

Ladies and Gentlemen, tonight we pay homage to Frederick William Lanchester, Doctor of Laws, Fellow of the Royal Society who, having become interested in mechanical flight at the age of 21, while studying at South Kensington in 1889, entered the field of aeronautics in 1892 and continued to aid its development until his death in 1946. His great contributions to aeronautics were the discovery of the theory of the vortex motion of the lifting wing and that the key to successful flight lay in reducing the skin friction, which was far from being the negligible quantity that others such as Langley, whose name is forever remembered through NASA Langley Field, had stated earlier. All this was in 1893 to 1894 some ten years before the first flight of the Wright brothers. When asked later how he had successfully derived his great and momentous theory Lanchester simply stated; ‘it was a matter of logical deduction helped by experiment’. He vigorously defended his work as not being empirical but was soundly based on hydrodynamic theory.

The interaction between vortices, sound and combustion can lead to self-excited oscillations of such large amplitudes that structural damage is done. These occur because any small unsteadiness in the rate of combustion is a source of sound, generating pressure and velocity fluctuations. However, the velocity fluctuations perturb the flame, thereby altering the instantaneous rate of heat release. Instability is then possible because while acoustic waves perturb the combustion, the unsteady combustion generates yet more sound! Combustion oscillations can occur in afterburners and at idle in conventional aeroengine combustors. Lean premixed, prevapourised technology has tremendous potential to reduce NOx emissions, but is proving highly susceptible to self-excited oscillations. An overview of the physics of the interaction between vortices, sound and flames is presented, and illustrated by examples of instability in generic premixed ducted flames and in aeroengine combustors. The potential for both passive and active control is discussed.

From Lanchester to the A380; from the era of the great pioneers to the integrated engineering teams and sophisticated analyses required to develop todays airliner. The ‘art’ of Aerodynamics has progressed a long, long way in the intervening century, but even with todays computational power it is still relevant to understand the basics and the early theories as developed by Lanchester and his contemporaries. In this lecture, the relevance of some of that early work and the compromises that must be made in optimising a modern wing design will be presented. These will include optimisation of spanwise loading, including trimming effects and winglets, and high and low speed aerodynamic and structural interactions, with examples drawn from the author's career in helping to develop the wings for the HS146 (now the RJX) and the Airbus family.

With the exponentially increasing computer power available over the last 30 years, the ‘art of compromise’ has progressively become the ‘science of optimisation’ and the lecture closes with a brief reference to techniques used to optimise current wing designs for the Airbus family.

This 2007 Lanchester Lecture covered a theoretical result, thought to be new and in print in the Journal of Fluid Mechanics, and some lines of thought on the interpretation of induced drag and recurring paradoxes which interfere with teaching ‘how wings work’. Some of these were presented in the author's 1998 Annual Review. The difficulties are not confined to drag, but also concern lift; they are no less severe in two dimensions than in three. The flow-field in the far wake of an aircraft is examined with the primary purpose of identifying lift and drag in a simple and unified manner, preferably an intuitive one acceptable by novices (and even by those who mind using Bernoulli's equation!).

In France, the very first ideas on flow control were developed by Philippe Poisson-Quinton from the Office National d'Etudes et Recherches Aérospatiales (ONERA) in the 1950s. There was some renewal of this research topic in the early 1990s, first in the United States with scientists like Wygnanski and Gad-El Hak, and also in France at the initiative of Pierre Perrier from Dassault Aviation, who triggered a lot of research activities in this field both at ONERA and in the French National Centre for Scientific Research (CNRS) laboratories. The motivation was driven by the applications on Dassault Aviation military aircraft and Falcon business jets in order to contribute to the design, while facilitating performance optimisation and multi-disciplinary compromise. A few examples of flow control technologies, such as forebody vortex control, circulation control, flow separation control or boundary layer transition control using hybrid laminar flow control (HLFC), are presented to illustrate the applications and to explain the methodology used for the design of the flow control devices. The author also emphasises the current reaction of industry with respect to the integration of flow control technologies on an aircraft programme. The conclusion is related to the present status of the French research on this topic and to the next challenges to be addressed.

This contribution is based on the Lanchester Lecture of the Royal Aeronautical Society held in Manchester, UK, in October 2009. The lecture reflected on further possible perspectives for aeronautical research, in particular with respect to aerodynamics. The air transport system of today has matured to very high performance and safety standards. However, due to the ongoing global developments of economy and ecology, new challenges have to be faced. Thus, the relevance of all engineering aeronautical disciplines contributing to the final aircraft configuration is now closely scrutinised, and especially aerodynamics is challenged whether any investment in further research is still justified. In this contribution, it is argued that, when carefully exploited, aerodynamics still offers a substantial technological perspective, well beyond the concepts for the next generation of aircraft as currently being pursued. As an example, the aerodynamics of a forward swept-wing are discussed and it is outlined that, when combining the transonic characteristics of a forward swept-wing with the advantages of natural laminar-flow, considerable improvements in efficiency may be gained. However, this potential may only be leveraged through a strategic, long-term orientation of fundamental and applied research.

In the coming century, the impact of air travel on the environment will become an increasingly powerful influence on aircraft design. Unless the impact per passenger kilometre can be reduced substantially relative to today’s levels, environmental factors will increasingly limit the expansion of air travel and the social benefits that it brings. The three main impacts are noise, air pollution around airports and changes to atmospheric composition and climate as a result of aircraft emissions at altitude. The lecture will review the work done within the Air Travel – greener by Design programme to assess the technological, design and operational possibilities for reducing these impacts. The main aeronautical disciplines all have something to contribute but it is in aerodynamics that the greatest opportunities appear to lie. If these opportunities are pursued, the aircraft in production in 2050 could be very different from those of 2005. It is for the aerodynamicists, supported by the structures and systems engineers and the materials scientists, to make the case for a radical leap.

A summary of the ways in which aviation impacts the environment is presented and the ratio of the energy liberated during a flight to the revenue work done (ETRW) is identified as a key indicator in the assessment of environmental impact. Using the ‘Breguet’ range equation, a number of theorems relating to ETRW are derived and discussed. This is followed by an approximate analysis to produce estimates for the ETRW of aircraft currently in service. It is found that the global fleet average value for ETRW is much higher than those estimated for existing individual aircraft. An explanation of the difference is presented, with the contributions from airline operations and air traffic management identified and quantified. Consideration is then given to the potential for future reduction in ETRW through advances in materials, alternative fuels, structures, aerodynamics and propulsion technologies and the likely benefits are quantified. The improvement in ETRW that could be achieved if this parameter was minimised in the design process with the current level of technology is also considered. Finally, the likelihood of performance improvements being introduced in the short, medium and long term is briefly discussed.