Structural dynamics is a key discipline in aircraft design and certification. The realm of structural dynamics includes problems in which structure flexibility is important, such as dynamic loads (landing, taxi, gust, turbulence...), but it also includes other areas like environmental vibration or impacts technology. This is closely related with its sister discipline Aeroelasticity.

Linearity has been the cornerstone assumption in aircraft design engineering solutions. In the past, linearity allowed to solve many structural dynamics problems that otherwise would have been unaffordable. Nowadays, the necessity of highly optimised structures, combined to an increase of computer power, has made this assumption to be reconsidered.

This paper presents a wide survey on non-linear topics in structural dynamics and the way they have been solved at EADS-CASA (Airbus military) in the past 25 years. Although the paper has been mainly focused on numerical simulation using the Finite Element Method technique, component tests and full aircraft tests are also presented.

In this paper, the results of computational studies on the unsteady flow features in three-dimensional empty cavities and cavities with a representative store are presented. Flow simulations with a turbulence model based on a hybrid method, which behaves as a standard Reynolds-averaged Navier-Stokes (RANS) model within the attached boundary layer and as a Large-Eddy Simulation LES sub-grid scale model in the rest of the flow (commonly known as Detached-Eddy Simulation (DES)) are used in this study. The time-mean flow study showed the presence of three-dimensional effects inside the cavities. The mean flowfield visualisation also clearly showed the presence of a pair of ‘tornado-like’ vortices in the upstream half of the cavity which merge to a single, large recirculation further downstream. Visualisation for the cavity-with-store case revealed that the mean flowfield was effectively divided into two halves with significant reduction of the spanwise flow across the cavity width. In the unsteady flow study, near-field acoustic spectra were computed for the empty cavity and cavity-with-store cases. Study of unsteady pressure spectra for the cavity-with-store case found the presence of many peaks and the corresponding mode frequencies were found to agree well with the Rossiter modes. The blockage effect of store and strut on the spanwise flow is thought to have reduced the interaction, and subsequent non-linear coupling, between the Rossiter modes. This may be the reason for the co-existence of multiple modes without the coupling among them.

This paper presents a feasibility study to integrate a developed lift system (an annular wing wrapped around a centrifugal flow generator) into a Vertical/Short Take-Off and Landing V/STOL aircraft. Different physical scales, from micro aerial vehicle to a Harrier Jump Jet scale, for a variety of propulsion systems are explored. The system has shown to be viable for several classes of aircraft but with better performance offered by a micro-aerial-vehicle (~40g) and a large vehicle (~10,000kg) with a turbofan engine, albeit in both cases with apparently worse performance than is offered by current technologies. The wingform does not appear to be feasible in the light aircraft scale whilst using internal combustion engines.

Micro air vehicles (MAVs) are typically of low mass and moment of inertia and have flight speeds comparable to birds and the larger insects. Such craft traverse the lower levels of the atmospheric boundary layer (ABL) which is a significantly different environment than that experienced by larger manned aircraft, which spend the majority of their time in relatively clean air and fly at speeds significantly higher than typical wind speeds in the ABL. Here a new series of measurements dedicated to understanding spatial and temporal velocity fields that MAVs experience are presented. Atmospheric wind measurements were taken by sampling four multi-hole dynamic pressure probes spanned perpendicular to the oncoming wind at spans of between 0·014m and up to 0·45m. It was noted that the variation of both longitudinal velocity and flow pitch angle against spacing followed a fractional power law and as such large variations were present even for the smallest inter-probe separations. This effect is thought to explain the increasing piloting difficulties experienced in maintaining good roll control for decreasing scales of craft.

The influence of angle-of-attack and vortex-aerofoil vertical miss-distance on the aerofoil-vortex mechanism of interaction is investigated numerically using the large-eddy simulation approach. The study concerns the aerofoil-vortex interaction (AVI) phenomena encountered in the rotorcraft aerodynamics. The studies are performed for a Reynolds number of 1·3 × 106 based on the chord (c = 0·2m) of the aerofoil and free-stream velocity U = 100ms−1. The studies are conducted for three different angles-of-attack (α = 0°, and α = 5°, α = 10°) and vertical miss-distances (h = 0·0m, h = −0·01, h = −0·02m) respectively. The present study shows that the magnitude of lift coefficient and flow separation, at the instant of interaction, decay with the increase of angle-of-attack and vertical miss-distance.