A theoretical investigation is made of the onset of buoyancy-driven convection in a circular cylinder. Amplitude equations are derived for the weakly nonlinear evolution of critical disturbances at moderate values of the radius-to-height ratio. It is shown that the initial form of the convective motion a t Rayleigh numbers slightly above critical is not axisymmetric. Particular attention is paid to the neighbourhoods of points where two disturbances are simultaneously critical according to linear theory; the nonlinear evolution in such neighbourhoods is studied in detail.

Applications of hot-wire anemometers to velocity rneaaurements near walls can result in erroneous velocity data owing to additional heat losses to the wall. It is difficult to account for these errors if calibration data are used that were obtained in calibration test rigs without walls. This has been recognized in many studies in which hot-wires were applied to measurements in wall boundary-layer flows and different suggestions for corrections have been given. The present paper summarizes these suggested corrections and points out existing differences. It is also shown that some hot-wire measurements have been performed without any corrections being applied and reasons for this are given. Whereas most of the existing suggestions for wall corrections of hot-wire data are based on experiments, the present approach uses results of a numerical study.

Assuming the problem to be two-dimensional and that the wire can be replaced by a line source of heat, a numerical study is carried out for the temperature distribution downstream of the wire, and computations are performed for the heat loss from the wire in presence of the wall. Computations are performed for two Merent boundary conditions representing ideally conducting and non-conducting materials. These different boundary conditions yield large differences in the computed heat losses from the wire, and these explain the existing differences in the experimentally obtained corrections. The numerical study also shows that the large heat losses for conducting walls are due to the distorted temperature distribution in the temperature wake of the wire.

Some of the results of the numerical studies were experimentally verified by the authors and a procedure haa been developed to correct instantaneous hot-wire readings for additional heat losses to a wall. For non-conducting walls, the heat losses are much smaller and are negligible for most practical measurements.

We consider possible mechanisms for the observed secondary instability of travelling instability waves in liquid fluidized beds. The resonance conditions for quadratic nonlinear interaction are solved in the long-wave limit by perturbation theory. The estimated horizontal wavenumber of the resonant sideband agrees well with experiment and supports the proposed mechanism.

The Navier–Stokes equations are solved numerically for two-dimensional peristaltic flows by using the finite-difference technique employing the upwind SOR method, and the velocity, pressure and stress fields for various peristaltic flows are obtained. The influences of the magnitudes of wave amplitude, wavelength and Reynolds number on the flow are investigated through numerical calculations, and the results are compared with those of the perturbation analysis. The paper is mainly concerned with elucidating the characteristics of the peristaltic flow at moderate Reynolds numbers where peristaltic pumping has a possibility of engineering application. As a result, it is found that the validity of the perturbation solutions by Jaffrin (1973) and Zien & Ostrach (1970) are restricted within a narrower range than that which they predicted, and that the reflux phenomenon in the flow does change the whole situation according to Reynolds number.

An inviscid model for the Karman vortex street, containing vortices of uniform vorticity surrounded by irrotational fluid, is related to the wake behind a bluff body by a global analysis requiring the conservation of momentum, energy and vorticity. Some comparison is made with experimental results reported in the literature. A qualitative procedure is proposed whereby the slow evolution of the wake through viscous effects is approximated. Some comments are made regarding the relevance of the stability properties of the inviscid street. Some calculations are made for the ‘secondary vortex street’ that is observed after breakdown and rearrangement, and comparison is made with experiment.

The stability of a vortex street consisting of two parallel rows of staggered arrangement is investigated by taking account of the effects of the finite core of the vortex. A finite stable region of the transverse-to-longitudinal spacing ratio k is found around 0·281, the value obtained by Kármán. As the core size increases, this stable region moves to larger k. The width of the stable region also changes with the core size S/l2, where S is the area of the core and l is the longitudinal spacing of the vortex street. It is null at S/l2 = 0, increases at first in proportion to the square of S/l2, takes a maximum value at S/l2 ≃ 0·08, then decreases to zero at S/l2 ≃ 0·11. For still larger values of S/l2 [gsim ] 0·11, it increases again rather rapidly. The wavenumber of the disturbance having the maximum growth rate is shown to be in complete agreement with that of a growing’ disturbance recently discovered in a vortex street behind a circular cylinder.

Electrochemical measurements of the local wall shear were made along the inner bend of a curved pipe in the entry region, to examine the nature of the secondary-flow boundary-layer collision. Analysis by Stewartson, Cebeci & Chang (1980) predicts a vanishing of the wall shear at the collision point, but without flow reversal. The experimental results are in good agreement with the analytical predictions upstream of the collision point, and its location appears to be predicted accurately. However, downstream of the collision point agreement is poor.

The European Mechanics Colloquium, Euromech 142, ww held at the Ecole Centrale de Lyon from 23 to 26 September 1981 and WM attended by 70 participants, from 9 countries, active in the fields of (i) sound production by turbulent flows and (ii) the effects of flow and turbulence on the propagation of acoustic waves. For topic (i), attention was mostly paid to shear-layer and jet instabilities and to the flow-surface interaction of flexible boundaries, vibrating blades and rigid thick airfoils. Applications were concerned in particular with propeller noise and airframe self-noise of large aircraft. Impinging shear layers were also considered for single and multiple cavities in which self-sustained oscillations can occur. Another subject discussed at the meeting was the noise from inhomogeneities, with applications to flames. For topic (ii), theoretical formulations were presented for the far field of moving multipole sources in the presence of flow and for sound propagation in ducts of variable cross section, with flow, for frequencies around the cut-off. The effect of turbulence was investigated in terms of the space–time coherence of the transmitted pressure fields. Broadband active sound control in the presence of flow was also considered, with emphasis on the progress made possible by use of digital filters. Finally, new experimental techniques, such as acoustic intensity measurements, were presented and large anechoic wind tunnels and other acoustic facilities were described.