The passive control of a shock wave-boundary-layer interaction involves placing a porous surface beneath the interaction, allowing high pressure air from the flow downstream of the shock wave to recirculate through a plenum chamber into the low pressure flow upstream of the wave.

The simple case of a normal shock wave at a Mach number of 1·4 interacting with the turbulent boundary layer on a flat wall is investigated both experimentally and numerically. The experimental investigation made use of holographic interferometry, while the computational section of the investigation made use of a Navier-Stokes code to derive pressure gradients, boundary-layer properties and total pressure losses in the interaction region. It is found that the structure of shock wave-boundary-layer interactions with passive control consists of a leading, oblique shock wave followed by a lambda foot. The oblique wave originates from the upstream end of the porous region, and its strength is determined by the magnitude of the local blowing velocities. The shape of the lambda foot depends on the position of the main shock relative to the control region, resembling an uncontrolled foot when the main shock wave is towards the downstream end of the porosity, but becoming increasingly large as the shock moves upstream and eventually merging with the leading, oblique shock to form a single, large, lambda structure.

Improved forms of passive control are suggested based on the findings of this investigation, including the use of passive control systems which incorporate streamwise variations in the level of porosity.

For the past 50 years civil air transport has been dominated by the combination of the gas turbine and the B-47 airframe configuration. Both these machines owed their creation to WW2 and both represented revolutionary concepts at the time. Oyer the years, the engine and the airframe have undergone considerable detailed refinement. The changes have resulted in very impressive improvements in performance. However, it is now very clear that both are close to some well defined asymptotic limits that bound their performance. The result is that further potential improvements are smaller in percentage terms, become harder to achieve technically and, consequently, come at increasingly higher cost.

A hugely successful global industry has developed around this standard configuration. Increasingly, more and more companies use aircraft and, as their businesses grow, the demand for aircraft and air transport increases. However, the ability of the environment to absorb this growth is beginning to be questioned and new ideas are required if aviation is to be regarded as an unbounded and a truly sustainable activity.

During the past decade, the Navy has considerably improved its capabilities in aircraft-weapon integration. In 1989 it took more than 400 hours of wind-tunnel testing, which cost $1,5000,000, and 20 flights to clear the JSOW from the F-18 to Mach 0·95. This year the Mk-83 JDAM was cleared after only 60 hours of wind-tunnel testing and five flights to the full F-18 aircraft envelope of Mach 1·3. This reduction occurred because the Navy not only learned to test smarter, but also developed an integrated approach to modelling and simulation (M&S), wind-tunnel and flight testing which allowed lessons learned on previous programmes to be applied to new ones. However, the present approach still requires a fairly large commitment of time and financial resources to accomplish the mission.

The present approach has optimised the use of available resources; any further gains will have to come not by improving existing techniques, but by bringing new resources into the process.

A two step procedure is proposed for the design of nonlinear aircraft control systems. A classical design is first denned, based on a linearised aircraft model, and easily optimised by means of standard approaches. An outer-loop nonlinear controller is then used to enhance the whole control system. This latter controller is based on fuzzy logic rules and is of fixed structure. Its behaviour is based on the choice of a set of parameters that may be tuned by means a genetic algorithm based routine. The whole methodology is simple to handle and may be effectively used to give quick and efficient responses to the designer. The procedure has been verified with a couple of examples: the obtained results clearly show important improvements with respect to a classical methodology.

The paper reviews present practices in the prediction of scale effect at transonic speeds and considers how these may have to change in the future in the light of possible changes in wing design standards. Particular issues highlighted in the paper include the research that is needed to obtain the potential benefits that should come from the ability to test models at near-full-scale Reynolds numbers in cryogenic tunnels such as the ETW and second, the different experimental techniques that may have to be introduced if aerodynamic designers attempt to realise their long-held ambition of obtaining extensive laminar flow in flight.

In a number of applications, turbulent boundary layers are exposed to a gradual or rapid acceleration. As a result of this, the flow may change to a laminarised state before retransitions again to a turbulent flow. This change of state (turbulent-laminar-turbulent) can have drastic effects on a variety of engineering problems. For example it has significant effects on the heat transfer rate at a boundary over which it is flowing, the mixing of fuel and air in the scramjet combustors, the mixing process in the wake of a transonic turbine blade and hence the base drag, etc.

An experimental investigation on the interference effect of lee-side balance housing bodies on the longitudinal aerodynamic characteristics of thin slab delta wings has been made using a special and novel thin three-component balance. This study has been conducted using wings with a t/c of 0.053 and sweep of 76°, 70° and 65° for three different lee-side bodies viz:Body (A), Body (B) and Body (C) of which Body (C) is the smallest. The testing was carried out at Mach number of 8·2, Reynolds number of 2·13 ˘ 106 and incidence of –4° to 12°. For the smallest body (Body (C)) tested, at the incidence at which this body first goes into the aerodynamic shadow of the wing (α = 6·5°), the difference in CN, CA, CM and L/D between the wing-body and the plain wing is around by 22%, 12%, 75% and 35% respectively. This difference decreases with increase in incidence and at the highest angle-of-attack up to which testing was done (α = 12°), the. corresponding values of CN, CA, CM and L/D are around 9%, 12%, 15% and 4% respectively. Contrary to the assumption in the literature pertinent to force measurements on thin slab delta wings, the interference of the lee-side bodies are found to be appreciable even after they come into the aerodynamic shadow of the wing.

This paper summarises our current understanding about the impact of aircraft emissions on the atmosphere and describes how the UK Natural Environment Research Council (NERC) Upper Troposphere/ Lower Stratosphere (UTLS) Ozone programme is contributing directly to research in this field. Understanding ozone change is a main focus of this research programme.

Ozone is a pollutant at the Earth's surface where it can lead to health problems, is a greenhouse gas and, in the stratosphere, it also shields the Earth from uv radiation. It is known that ozone has been severely depleted in the lower stratosphere (15-20km) over the poles due to increasing concentrations of man-made chlorine and bromine compounds (CFCs etc.). There has also been more limited ozone loss in the mid-latitude lower stratosphere but the reasons for this are less clear because ozone is governed by transport in and out of this region as well as chemistry.

The experiences and lessons learnt over the past twenty years developing a range of unstable unmanned aircraft are described along with the extensive use made of modelling and simulation in this development process. The scope for future developments is addressed and indicates even more on board intelligence is possible and desirable.

The National Aeronautics and Space Administration sponsored a joint High-Speed Research Programme with United States airframe and propulsion companies to provide the critical high-risk technologies for a Mach 2·4, 300 passenger civil transport. Laboratory and medium-scale tests provided promising results in meeting both the environmental and economic goals for a future High-Speed Civil Transport. However, before the technologies were integrated at large and full scale, the programme was cancelled because of global economic concerns of the US transport industry.

The two parts of this paper summarise the turbomachinery research undertaken at Pyestock during the 50 years since the National Gas Turbine Establishment was formed in 1946. The theoretical and experimental activities are described, and their influence on UK military and civil aero engines is assessed. The way in which NGTE supported non-aeronautical gas turbines is also explained. Part 2 covers turbines.

This paper describes and compares various analyses leading to the development of approximate models for the linear stability modes of the non-rigid airship. The progress of the analyses was variously dependent on assumptions made from the detailed scrutiny of linear numerical models for three airships. For each airship studied, the linear models were obtained from non-linear simulation models by linearising about a number of chosen trim speeds representative of a typical speed envelope. The decoupled linear models comprised the longitudinal and lateral-directional state equations of the neutrally buoyant airship, for speeds from the hover to 30m/sec. Since the fidelity of the earliest airship models was not known, the principal purpose of this paper is to re-visit the original analysis using a later airship model of known excellent fidelity.

The longitudinal modes of the airship comprise the surge mode, the heave-pitch subsidence mode and the oscillatory pitch-incidence mode. The lateral-directional modes of the airship comprise the sideslip subsidence mode, the yaw subsidence mode and the oscillatory roll pendulum mode. Approximate models for these modes are derived and expressed in terms of concise aerodynamic stability derivatives. The mode characteristics are discussed, and the approximate models are compared with the actual airship modes over the typical airspeed envelope.

If an aerofoil of chord c has a parabolic nose with radius of curvature r, and is placed at angle-of-attack α to a stream, the laminar boundary layer on its upper surface remains unseparated for α<0.8l8. In the present paper we consider some smooth local modifications to the leading edge. Symmetric modifications of the nature of local sharpening of the nose can improve this result to at least α<0.897. Further improvements are possible for unsymmetrical (e.g. drooped) noses, and an example of a ‘drooped’ nose with α<0.912 is shown.

The two parts of this paper summarise the turbomachinery research undertaken at Pyestock during the 50 years since the National Gas Turbine Establishment was formed in 1946. The theoretical and experimental activities are described, and their influence on UK military and civil aero engines is assessed. The way in which NGTE supported non-aeronautical gas turbines is also explained. Part one provides a general introduction and then covers compressors.