Recent developments in delta wing aerodynamics are reviewed. For slender delta wings, recent investigations shed more light on the unsteady aspects of shear-layer structure, vortex core, breakdown and its instabilities. For nonslender delta wings, substantial differences in the structure of vortical flow and breakdown may exist. Vortex interactions are generic to both slender and nonslender wings. Various unsteady flow phenomena may cause buffeting of wings and fins, however, vortex breakdown, vortex shedding, and shear layer reattachment are the most dominant sources. Dynamic response of vortex breakdown over delta wings in unsteady flows can be characterised by large time lags and hysteresis, whose physical mechanisms need further studies. Unusual flow–structure interactions for nonslender wings in the form of self-excited roll oscillations have been observed. Recent experiments showed that substantial lift enhancement is possible on a flexible delta wing.

Military aircraft, by definition, need to survive the onslaught of opposing forces to successfully complete their mission. From an aircraft perspective, the electromagnetic (EM) environment can be an enabler, via the use of navigation aids, radar, radio communications etc. – in fact mission success depends on its successful use. However, this environment is also potentially a disabler, as threat weapon systems and the environment itself can harm or destroy the aircraft. This paper discusses risks and hazards thus posed to aircraft survivability, partitioned into two classes – ‘direct’ and ‘indirect’ EM threats. ‘Direct’ threats are those that occur as a result of direct coupling of EM energy to the airframe and systems within, e.g. lightning strike and directed energy weapons. ‘Indirect’ threats are those that utilise EM sensors to detect, track and target the aircraft, e.g. radar-guided surface-to-air missiles. Airframe intrinsic mechanical vulnerability is also an important part of survivability, although not addressed in this EM-related paper. It is shown that risk and hazard can be minimised by gaining a thorough understanding of operational scenarios, developing holistic system-of-systems solutions to military requirements, and using best practice design and development techniques.

The design methodology and performance of Loughborough University’s new 1·9m × 1·3m, indraft wind tunnel is discussed in the following paper. To overcome severe spatial and financial constraints, a novel configuration was employed, with the inlet and exit placed adjacent to each other and opened to atmosphere. Using a fine filter mesh, honeycomb, two turbulence reduction screens and a contraction ratio of 7·3, flow uniformity in the working area of the jet at 40ms-1 is shown to be within 0·3% deviation from the mean velocity, with turbulence intensity in the region of 0·15%. Working section boundary layer characteristics are shown to be consistent with that of a turbulent boundary layer growing along a flat plate, which originates at the point of inflection of the contraction. A maximum velocity of 46ms-1 was achieved from a 140kW motor, compared to a prediction of 44ms-1, giving an energy ratio of 1·42. Comparison between theoretical and measured performance metrics indicate differences between the way modules perform when part of a wind tunnel system compared to data gathered from test rigs.

Thirty-eight data sets from static tests of various 65° delta wings in many water and wind tunnels are compared with four empirical vortex breakdown location prediction methods and the results of two Navier-Stokes computations to assess their range of validity in pitch. Vortex breakdown is the sudden expansion and subsequent chaotic evolution of the otherwise orderly, spiraling, leading-edge vortex flow over the upper surface. Large fluctuations occur in vortex breakdown location at static test conditions making accurate experimental determination difficult.

The prediction methods do not account for the seemingly minor geometric details that vary between the models such as thickness, leading-edge bevel angle and radius, trailing-edge bevel angle, sting mounting, instrument housings, etc. These geometric variations significantly affect the position of vortex breakdown and degrade the accuracy of the predictions. The large changes in the flow produced by small geometric changes indicate that an efficient flow control strategy may be possible. Many of the data sets are not corrected for tunnel wall effects, which may account for some of the differences. Data presented herein are as published by the original authors, without additional corrections.

An investigation of active control of the swept shock wave/boundary-layer interaction using ‘smart’ flap actuators is presented. The actuators are manufactured by bonding piezoelectric material to an inert substrate to control the bLeed/suction rate through a plenum chamber. The cavity provides communication of signals across the shock, allowing rapid thickening of the boundary layer approaching the shock. This splits the shock foot into a series of weaker shocks forming a lambda structure, thus reducing wave drag. Active control allows optimisation of the unimorph deflection, hence rate of mass transfer.

In this paper, results of the interaction using pressure sensitive paint (PSP) are emphasised. It is shown that the use of PSP, in conjunction with discrete pressure data, enables the main features of the interaction to be observed when the actuators are subject to different deflections.