AhstructRecent investigations have demonstrated that the settling velocity, w,, of a cylinder at low Reynolds numbers (the Stokes region) is given bywhere L and D are the cylinder length and diameter, ps is the particle density, and SL. and p are the fluid viscosity and density. This relationship is compared with published data on the settling velocities of cylindrical fecal pellets produced by euphausiids and copepods. The agreement between data and the equation is very good. The analysis further permits the indirect evaluation of the fecal pellet density. A mean density fi, = 1.22 g*cm-" was so determined, which corresponds almost exactly to the one reliable direct measurement of fecal pellet density (1.23 g.cm-"). A second equation is available that can be used if the fecal pellets are ellipsoidal or oval rather than cylindrical.It is well established that the settling of fecal pellets produced by copepods, euphausiids, and other organisms in the sea is important in controlling the vertical distributions in the water column of many different elements and materials (organic carbon, 0,, C02, PCBs, artificial radionuclides, etc.), and in contributing to the bottom sediments (e.g. Schrader

Laser-Doppler anemometry has been used to quantify the mean velocity and turbulence characteristics of the isothermal, incompressible flow within a piston-cylinder arrangement motored without compression at 200 rpm and with idealized inlet geometries corresponding to a pipe and to an annular port located in the centre of the cylinder head. The results indicate that the pipe entry gives rise to a strong vortex near the piston as the indrawn air is deflected radially along the piston face and cylinder wall; this, in turn, gives rise to a weaker, counter-rotating vortex near the cylinder head which grows appreciably as the piston approaches bottom-dead-centre. With the annular-port entry, the inlet jet is angled and results in a flow pattern with a large vortex occupying nearly all of the flow space with much smaller vortices at the corners between the wall and the piston and cylinder heads. The effect of a piston bowl was also investigated for the port entry and is shown to be small.

Predictions of the isothermal, incompressible flow in the cavity formed between two corotating plane disks and a peripheral shroud have been obtained using an elliptic calculation procedure and a low turbulence Reynolds number k–ε model for the estimation of turbulent transport. Both radial inflow and outflow are investigated for a wide range of flow conditions involving rotational Reynolds numbers up to ∼106. Although predictive accuracy is generally good, the computed flow in the Ekman layers for radial outflow often displays a retarded spreading rate and a tendency to laminarize under conditions that are known from experiment to produce turbulent flow.

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A low turbulence Reynolds number k-ϵ model has been used in conjunction with an elliptic flow calculation procedure to obtain finite-difference solutions for radial outflow in the cavity formed between two plane corotating discs and an outer peripheral shroud. Air enters the cavity axially through a central hole in one of the discs and is assumed to leave via a uniform sink layer adjacent to the shroud. The main emphasis of the paper is the extension of the solution procedure to cover high rotational speeds, with rotational Reynolds numbers up to 107. As a necessary prerequisite to this exercise, the turbulence model is validated by its good predictive accuracy of existing experimental data up to a maximum rotational Reynolds number of 1.1 × 106.