The effects of peripheral-layer viscosity on the flow characteristics of a bio-fluid due to peristaltic transport has been investigated. It is shown that, for a given pressure drop, the flow flux increases and the frictional force decreases as the viscosity of the peripheral-layer fluid decreases. However, for zero pressure drop, the flux does not depend upon this viscosity while the friction force decreases as it decreases.

The analysis has been applied and compared with observed data.

A simple dye in water method has been used to visualize the growth of a two-dimensional starting flow vortex formed at a wedge-like sharp edge. Several cases were tested corresponding to different wedge angles and to different values of the time exponent in the velocity–time power law describing the starting flow. Photographic sequences showing the time-wise primary vortex growth are presented from which various secondary-flow details are identified. For the larger wedge angles these include a strong secondary vortex and in some cases a small separation bubble-like flow region immediately adjacent to the wedge apex. For a thin-wedge model the formation of what might be interpreted as small rotation centres along the outer turns of the primary-vortex shear layer is observed but these are not seen as a manifestation of an instability phenomenon in the fluid. Measurements of the trajectories of the primary-vortex centre are compared with the predictions of an inviscid similarity theory of the vortex growth. Although the appropriate Reynolds number in the present experiments was relatively low, comparison between theory and experiments is regarded as reasonable with differences being attributed to viscous effects absent in the similarity theory, and also to apparatus wall effects.

A Galerkin method is used to calculate the finite amplitude, steady, axisymmetric convective motions of an infinite Prandtl number, Boussinesq fluid in a spherical shell. Convection is driven by a temperature difference imposed across the stress-free, isothermal boundaries of the shell. The radial gravitational field is spherically symmetric and the local acceleration of gravity is directly proportional to radial position in the shell. Only the case of a shell whose outer radius is twice its inner radius is considered. Two distinct classes of axisymmetric steady states are possible. The temperature and radial velocity fields of solutions we refer to as ‘even’ are symmetric about an equatorial plane, while the latitudinal velocity is antisymmetric about this plane; solutions we refer to as ‘general’ do not possess any symmetry properties about the equatorial plane. The characteristics of these solutions, i.e. the isotherms, streamlines, spherically averaged temperature profiles, Nusselt numbers, etc., are given for Rayleigh numbers Ra as high as about 10 times critical for the even solutions and 3 times critical for the general solutions. Linear stability analyses of the nonlinear steady states show that the general solutions are the preferred form of axisymmetric convection when Ra is less than about 4 times critical. Furthermore, while the preferred motion at the onset of convection is non-axisymmetric, axisymmetric convection is stable when Ra exceeds about 1·3 times the critical value.

Calculated numerical results are presented for laminar buoyancy-induced flows driven by thermal transport to or from a vertical isothermal surface in cold pure and saline water wherein a density extremum arises. The present calculations specifically explore the consequences of temperature conditions wherein the buoyancy force reverses across the thermal region owing to the presence of a density extremum within the region. Such conditions commonly occur in terrestrial waters and in technological processes utilizing cold water. The linear approximation of density dependence on temperature, used in conventional analysis, is here replaced by a very accurate non-linear density equation of state for both pure and saline water. This permits an accurate treatment of such flows for bounding temperatures up to 20 °C at ambient salinity and pressure levels from 0 to 40 p.p.t. and 1 to 1000 bars, respectively. The results may be applied to the melting or slow freezing of a vertical ice surface in pure water as well as to a heated or cooled vertical isothermal surface in pure or saline water. For example, buoyancy force reversals arise for a vertical ice surface at 0 °C melting in fresh water between 4 °C and 8 °C at atmospheric pressure. Temperature conditions for which buoyancy force reversals occur are of special interest because of the resulting anomalous flow behaviour and low surface heat-transfer rates. The transition from conditions with no buoyancy-force reversal to those resulting in a large buoyancy-force reversal is accompanied by as much as 50% decrease in surface heat transfer. This produces a corresponding trend in the melt rate of a vertical ice surface in pure water. Sufficiently strong buoyancy force reversals are found to cause local flow reversal either at the edge of the flow layer or near the surface. Conditions are determined for which flow reversals occur at each of these locations. These local flow reversals are the precursors of convective inversion, that is, of the reversal of the net flow direction with changing ambient medium temperature. Limits on conditions for convective inversion are determined. Calculated transport is compared with previous experimental results, with good agreement throughout the several regions of such complicated flows. The calculations indicate that such flows are relatively very weak. However, their form may lead to early laminar instability.

Measurements of wall pressure fluctuations under a turbulent boundary layer were made on the fuselage of a sailplane. This flow offers a noise-free environment with a low free stream turbulence level. The axisymmetric boundary layer undergoes natural transition and develops in a zero pressure gradient region. Spectra of the wall pressure were found to decrease at low frequency in agreement with calculations based upon a turbulence–mean shear interaction mechanism. Velocity fluctuations at several positions within and outside the boundary layer were measured and correlated with the wall pressure. A special conditional correlation method was also employed to find the contribution of various velocity fluctuations to the wall pressure. A conditioning signal was formed based upon the signs of u and v and the turbulent–non-turbulent nature of the flow. This signal was time lagged and correlated with the wall pressure signal. It was found that in the outer portion of the boundary layer (y/δ > 0·5), irrotational motions were more highly correlated with the wall pressure than vortical motion.

This paper is concerned with understanding the development of a free surface and the velocity of a thick creeping film emerging from a slit onto a plate. There is a difference between free surface flows with film thickness of 10 to 20 mm and thin film flows of less than 1 to 2 mm due to surface tension influence.

A laser–Doppler velocimeter of high spatial and temporal resolution has been used to measure the decreasing thickness of slowly flowing liquid and the velocity profiles at the exit of the slit and in the transition region of the plate. The hydrodynamic entrance length can be calculated from an empirical dimensionless relation that includes only the plate inclination angle β as a parameter.

This paper describes an analysis of the forces induced by separation and vortex shedding from sharp-edged bodies in oscillatory flow at high Reynolds number. The analysis which is valid for the case of small oscillations of the fluid is compared with experimental data obtained at fairly low Keulegan–Carpenter numbers.The main conclusions of this paper were presented at the International Symposium on Wave Induced Forces on Structures at Bristol, 1978.

The design of most aerodynamic surfaces, as for example the helicopter rotor, is based essentially on quasi-steady theories. However, the dynamics of a rotating blade introduce unexpected fluctuations and overshoots of properties like lift, drag, etc. The phenomenon of unsteady stall is intimately connected with the development of an oscillating boundary layer and separation. Experimental investigation of such flows was undertaken by a method of visualization developed especially for the study of laminar or turbulent boundary layers and separation. The method captures the instantaneous two-dimensional flow field, including regions of separated flow, and provides accurate quantitative information. Laser-doppler anemometer measurements complement the optically obtained data. Results reveal that separation responds with time-lag to external disturbances, in agreement with unsteady stall data. Oscillating outer flows result in displacement of the point of separation and, under certain conditions, the Despard & Miller (1971) criterion was found to hold. Earlier theoretical models of separation are confirmed qualitatively and for the early stages of the transient phenomena. The findings provide physical insight and quantitative data that may help explain the phenomenon of unsteady stall and unsteady separation.

An examination of the isotropic vorticity theory was made in an adverse pressure gradient flow based on experimental data obtained in a conical diffuser having a total divergence angle of 8° and an area ratio of 4:1 with fully-developed pipe flow at entry. The results showed that the rates and the ratio of production and dissipation of the turbulent vorticity were constant in the core region of the diffuser but increase significantly in the wall layer. The overall vorticity balance was essentially the same at all axial stations. The analysis of Batchelor & Townsend (1947) for isotropic vorticity was found to be valid in the core region of the diffuser for an order-of-magnitude higher Rλ (200 [les ] Rλ 600) than in grid turbulence. The magnitude of the skewness of ∂u1/∂t was constant in the core region and comparable to that for grid turbulence. Also, this region of constant skewness extended over a larger portion of the flow cross-section compared to pipe flow. On the basis of these results, it was concluded that assumptions of isotropy in the fine structure are valid in the core region of the diffuser.

In view of the importance of concentration fluctuations in practical and theoretical problems of turbulent diffusion, there are presented here some invariant properties of the distribution of fluctuations associated with a cloud of contaminant containing a finite quantity Q of material. These properties are invariant provided only that Q is conserved, no assumption whatsoever being made about the random turbulent velocity field. Consequences of the results for (i) steady plumes, (ii) the representation of the distribution of concentration by series of (generalized) Hermite polynomials, and (iii) the relationship of the ensemble mean concentration with the distance–neighbour function, are discussed using experimental evidence.