Necessary conditions for linear stability of a rotating, compressible and inviscid fluid are found by the generalized progressing wave expansion method. The full three-dimensional problem involving an arbitrarily given rotational symmetric external force field is considered for an arbitrary steady shear flow with vanishing axial velocity. The results obtained are compared with previously known results.

By the use of Green's theorem, relations are derived for the interaction of regular waves with a body in a canal. These relations are then applied to the problem of wave-power absorption by a body in a canal; this being taken as a model of an infinite row of wave-power absorbers. Two particular shapes of wave-power absorber are studied by use of thin-ship approximation. It is shown that the efficiency of power absorption by. a body in a canal may be much reduced when there is more than one travelling wave mode present in the canal.

Autorotation of an elliptic cylinder about an axis fixed perpendicular to a parallel flow is explained in this paper by means of numerical solutions of the Navier-Stokes equations. Potential-flow theory predicts, for constant angular velocity, half a period in which a torque supports rotation and half a period in which it opposes rotation, with vanishing torque in the average. This balance is disturbed by viscous-flow effects in such a way that, for a given angular velocity, vortex shedding either damps rotation or, under certain conditions, favours rotation. The proper interplay of those conditions, which include synchronization of vortex shedding and rate of rotation, results in auto-rotation. The numerical results for Re [les ] 400 are compared with experimental data for Re = 90000 from the literature. The agreement of the force coefficients and the large-scale flow patterns is surprisingly good.

The 120th Euromech Colloquium on experimental techniques pertaining to sizing and tracking of submicron- to millimetre-sized particles suspended in fluids was held at Lyngby on 20–22 August 1979 with forty-one participants from ten countries. Twenty-seven papers were presented during the two-and-a-half day meeting. Techniques included optical and acoustical sizing and velocity measurements, tracking, sedimentation and deposition of particles in various gas and liquid flows.

General relations are derived for the forcing of a mean zonal flow in a damped rotating barotropic system through the action of weak eddies. In particular it is found that if the eddies are forced at localized latitudes the induced motion away from these latitudes is likely to be counter to the rotation (i.e. ‘easterly’). Over the forcing latitude the mean motion is always westerly except when the forcing provides a sink of relative momentum. In the case when the background field is deformed topographically to generate eddies the divergence of the Reynolds stress is balanced at lowest order by a dynamic pressure drag, and the mean motion takes the direction of propagation of the forcing.

The relations are applied to a linearized Rossby wave field in a viscous fluid driven by a moving system of boundary sources and sinks or hills and hollows. The results are compared with laboratory experiments. All major predictions are confirmed qualitatively, but the discrepancies in detail indicate the influence of nonlinear effects other than those incorporated in the theory.

A set of self-similar solutions for blast waves associated with the deposition of variable energy at the front is presented. As a consequence of self-similarity, the results are applicable when the ambient atmosphere into which the wave front propagates is at a negligibly low pressure and temperature. Besides the class of (1) blast waves associated with energy gain that covers a regime bounded on one side by the well-known solution for adiabatic strong explosion waves (ASE) and, on the other side, by the solution for waves having the Chapman–Jouguet condition established immediately behind the front, included within the scope of our analysis are two others: (2) blast waves associated with energy loss that occupy a regime between the ASE solution and the case of infinite density ratio across the front, and (3) a non-unique class of solutions for blast waves associated with energy deposition that may have either locally sonic or supersonic flow immediately behind the front, extending over the regime between the waves headed by the Chapman-Jouguet detonation and the case of infinite rate of energy deposition. Specific results for a number of representative cases are expressed in terms of integral curves on the phase plane of reduced blast wave co-ordinates, as well as in the form of particle velocity, temperature, density, and pressure profiles across the flow field.

A useful parametrical model for the vertical structure of the pressure field induced by wind blowing over a field of surface gravity waves is proposed. The model is a linear expansion in a set of empirical orthogonal functions, derived from a set of 110 complex pressure profiles computed according to the theory of Miles (1957), and provides a compact, quantitative description of those profiles. The model has been used as an element in the analysis of a body of experimental data on wave-induced atmospheric pressure fluctuations obtained by Snyder et al. (1980).

A nonlinear three-dimensional boundary-layer problem governing the flow upstream of a particular disturbance (e.g. a shallow obstacle) at the wall is considered. The upstream response, a free interaction, takes place under zero displacement of the boundary layer, and the solution is found numerically using Fourier series truncation and varying the number of terms kept in the series. In one part of the flow field regular separation is encountered, beyond which the motion becomes strongly attached to the wall elsewhere in the flow field. Analytically, local structural investigations then suggest that the attached part of the upstream response terminates at a line singularity, while the separated part can continue indefinitely far downstream. The former structure leads to a new set of similarity solutions of the three-dimensional boundary-layer equations, while the latter develops a vortex sheet formation. The three-dimensional flow problem has most relevance to pipe flows, but some connexion also with external flows, and the implications for these are discussed.