The paper presents an investigation of flow instabilities occurring in shock-wave propagation and interaction with the walls of an enclosure. The shock-wave propagation is studied in connection with perturbed and unperturbed cylindrical blasts, initially placed in the centre of the enclosure, as well as for three different blast intensities corresponding to Mach numbers Ms = 2, 5 and 10. The instability is manifested by a symmetry-breaking of the flow even for the case of an initially perfectly-symmetric blast. It is shown that the symmetry-breaking initiates around the centre of the enclosure as a result of the interaction of the shock waves reflected from the walls, with the low-density region in the centre of the explosion. The instability leads to fast attenuation of the shock waves, especially for smaller initial blast intensities. The computations reveal that the vortical flow structures arising from the multiple shock reflections and flow instability are Mach number dependent. The existence of perturbations of large amplitude in the initial condition strengthens the instability and has significant effects on the instantaneous wall pressure distributions. The computational investigation has been performed using high-resolution Riemann solvers for the gas dynamic equations.

In this paper we present a Bayesian belief network (BBN) socio-technical model for investigating the accident rate for multi-crew civil airline aircraft. The model emphasises the influence of airline policy and societal behaviour patterns on the pilots within the piloting system. The main claim of this paper is that a BBN can be used to bring most aviation safety-critical elements into a common quantitative safety assessment despite the unique problems posed by the very low probability of accidents. We support this claim by replicating certain phenomena such as the low accident rate, the difference between the ‘more’ and ‘less’ safe airlines and other statistical factors of civil aviation. In particular, the model succeeds in explaining the large gap of six to seven orders of magnitude between in-flight measurements of pilots’ error and accident rate.

This paper looks at active control of the normal shock wave/turbulent boundary layer interaction (SBLI) using smart flap actuators. The actuators are manufactured by bonding piezoelectric material to an inert substrate to control the bleed/suction rate through a plenum chamber. The cavity allows rapid thickening of the boundary-layer approaching the shock, which splits into a series of weaker shocks forming a lambda shock foot, thus reducing wave drag. Active control allows optimisation of the interaction, as it would be capable of either positioning the control region around the original shock position using a series of unimorph flaps or fixing the shock position by controlling the rate of mass transfer.

The level of control achieved by unimorph piezoelectric actuators is not large because of small amounts of deflection possible. It is believed that to provide optimal control a piezoelectric material, which can provide greater strain and hence higher amounts of deflection is needed. However, currently such a piezoelectric material is not commercially available.

Theoretical quantification of viscous effects in fluid flows is difficult, even if turbulence is absent, except when it is legitimate to simplify the Navier-Stokes equations in some way; for example by invoking the boundary-layer approximation in appropriate cases of interacting viscous and inviscid flow. The technical importance of viscous effects was thought sufficient incentive to re-examine a very simple flow configuration — namely plane, uniform and steady flow of an incompressible, viscous fluid toward a vanishingly-thin flat plate aligned with the undisturbed stream — in search of fresh insights into the general theory for viscous-inviscid interactions.

The strategy was to exploit the analogy between vorticity transport in a viscous fluid and heat conduction in a moving solid. The key to doing so was the realization that, if the perturbation of the undisturbed flow by the plate might be represented as the sum of a series of successive approximations, then the stream function of the viscous part of the flow field — not merely the vorticity which resulted from its existence — might be expressible at every stage as the solution of an analogous heat conduction problem.