Modification of grid-generated turbulence by solid particles

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Abstract
The effects of almost neutrally buoyant plastic particles and heavy glass particles on grid-generated turbulence were studied experimentally in a water flow facility. From measured velocities of both the solid and liquid phases, drag and slip velocities of the particles and energy spectra and dissipation rates of the liquid phase were estimated. A monotonic increase in the dissipation rate of the turbulence energy with particle concentration was observed. The increase in energy dissipation rate for suspensions of glass particles was about twice that of suspensions of plastic particles. The increase in dissipation was larger than that predicted by a simple model based on the slip velocities between the phases. It is speculated that the particles enhance the transfer of energy to smaller eddies extending the dissipation spectrum to smaller scales. Since only part of the high wavenumber end of the energy spectrum could be resolved, this speculation cannot be conclusively demonstrated by the present experimental data. The measured velocity spectra do show that the particles increase the isotropy of the flow field and modify the high wavenumber end of the turbulence energy spectrum.

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