Turbulence attenuation by small particles in the absence of gravity

Abstract

Some examples of particle-laden turbulent flows that can be found in nature and industry include dust storms, chemical reactors, and pollutant abatement systems. In these type of flows particles are not only dispersed by the turbulence but they may also affect it in such a way that the carrier-phase turbulence level may be modified. Depending on the flow conditions and particle characteristics, augmentation and attenuation of turbulence levels have both been observed. Turbulence attenuation can become a problem if high turbulence levels are required, in areas such as heat transfer and mixing. Kulick et al. (1994) and Paris and Eaton (2001) have shown that the carrier-phase turbulence level can be attenuated up to 80% by a dilute dispersion of particles that has negligible volume fraction. The addition of an extra phase to a turbulent flow poses a very complex problem, however, and it is still not clear what causes this phenomenon of turbulence attenuation. Previous researchers have attempted to use optical measurements in simple flows to study this problem. Parthasarathy and Faeth (1990), Mizukami et al. (1992) and Chen et al. (2000) created stationary homogeneous turbulence by dropping particles through stagnant water, air, and a counterflowing upward wind tunnel, respectively. The carrier-phase velocity fluctuations depended only on the viscous dissipation rate, which was obtained from the potential energy loss of particles and particle drag. Grid-generated turbulence has also been investigated. Schreck and Kleis (1993), Geiss et al. (2004) and Poelma et al. (2006) observed turbulence modification using laser Doppler velocimetry (LDV), phase Doppler anemometry (PDA), and particle image velocimetry/particle tracking velocimetry (PIV/PTV), respectively. Nishino et al. (2004) created a nearly stationary dispersion of particles using an upward water flow and eliminated the transfer of potential to kinetic energy of settling particles. The ideal environment to study turbulence attenuation by particles would be in stationary homogeneous and isotropic turbulence without mean flow, in the absence of gravity so a stationary dispersion of particles