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Two-fluid turbulent dispersion models have been compared with direct numerical simulations (DNS) of a decaying turbulence bubbly flow in the low Stokes number limit, St≈10−3. Because of the absence of empiricism, DNS results represent an excellent means of assessing turbulent dispersion models. Sufficiently far away from the inlet of the channel, where the turbulence was fully developed, these turbulent dispersion models were able to predict the DNS results when a Schmidt number, Scb=0.83, was used. This result highlights the fact that even bubbles of diameter, Db=42 μm, considerably smaller than the Kolmogorov length scale, η=75 μm, do not behave as passive scalars for which Scb=1. In addition, these models were also assessed against a bubbly mixing layer flow having a low Stokes number, St

The lateral force on a tethered rigid sphere submerged in a turbulent, uniform shear flow of water was measured. Periodic and non-periodic motions of the sphere were observed depending on flowrate, shear and sphere density. The direction of the observed lateral force was opposite to that predicted by inviscid theory and increased in magnitude as the sphere’s Reynolds numbers based on relative velocity, Re ,a nd average shear, Rer, increased. The lateral force was found to correlate with the product Re Rer. The data suggests that a sign reversal occurs at relatively small values of the product Re Rer, where the lateral force is dominated by inviscid eAects. The results are explained assuming that the lateral forces on rigid spheres are a consequence of two competing factors: namely, inviscid lift forces and the vortex shedding-induced lateral forces which are dominant for higher Reynolds numbers. An estimate of the kinetic energy in the wake was used to show that the vortex shedding-induced lateral forces correlate with the product Re Rer and are in a direction opposite to the inviscid lift force. Combining the experimental data of this study with similar data a correlation for the lift coeAcient of spheres in turbulent shear flows was developed. This correlation is applicable to turbulent multiphase flows having a spherical dispersed phase. # 1999 Elsevier Science Ltd. All rights reserved.