Competitive pressures and economic constraints are driving aircraft manufacturers towards an ever-increasing exploitation of CFD for design, optimisation and prediction of off-design conditions. Such exploitation is favoured by rapid advances in meshing technology, numerical algorithms, visualisation tools and computer hardware. In contrast, the predictive capabilities of mathematical models of turbulence are limited — indeed, are often poor in regions of complex strain — and improve only slowly. The intuitive nature of turbulence modelling, its strong reliance on calibration and validation and the extreme sensitivity of model performance to seemingly minor variations in modelling details and flow conditions all conspire to make turbulence modelling an especially challenging component of CFD, but one that is crucially important for the correct prediction of complex flows.

The development of micro-air vehicles poses a considerable challenge to the materials scientist. Vehicles that may occupy less than 10cm in any direction require many structural components with dimensions well below 1mm when conventional engineering and assembly techniques are employed. As with conventional unmanned air vehicles (UAVs), and full-scale aircraft, materials that display a huge breadth of characteristics are required to build the airframe and to engineer sub-components, while meeting stringent mass and volume budgets. In particular, high modulus, high toughness, easy formability and jointing are desirable qualities. For larger structures, conventional foamed materials can meet some of these properties. However, the pore sizes in these conventional materials are too large to allow manufacture of micro-scale components, airframe sections and skins. This paper describes the manufacture and properties of some micro-foamed polymers, and polymer composites, metals and oxide ceramics that are being developed at DERA specifically for micro-vehicle applications.

The topological structure of an underexpanded Mach 2·5 jet injected into a Mach 0·75 crossflow are studied experimentally and numerically. The structure of the skin friction pattern is examined in detail by localising precisely the topological singularities. Oil-flow visualisations reveal the complex nature of the wall flow and its strong three-dimensionality. Four vortical structures appear in the vicinity of the wall, where two are essentially parallel to the wall (horseshoe vortex and boundary-layer vortices) and the other two are directed perpendicular to the wall (wake vortices). Comparison of computation with experiment shows good agreement for the complex separated-flow surface shear pattern and the pressure distribution. The crossflow Mach number plays an important role in the separation mechanisms. Significant differences in the topology occur with a Mach 0·3 crossflow whereas above Mach 0·6 the mean structure of the interaction is almost conserved, except that the secondary wake vortices disappear.

Classification of the winged aircraft according to the character of wing (blade) motion in horizontal and vertical plane is presented. Design of a rotor, the blades of which are driven into rotation via flapping motion similar to the movement of an ornithopter's wing is proposed and the principle of operation is considered. Mathematical model of the aerodynamics of the autorotating rotor with flapping blades in hover is made on the base of the helicopter rotor blade-element theory. Geometric and kinematic parameters influence on the rotor lift and efficiency is analysed. It is shown that in hover the efficiency of an autorotating rotor with flapping blades is approximately equal to the one of a helicopter rotor.