Transport mechanisms of turbulence energy in particle-laden channel flow (PIV measurements of interactions between particles and turbulence)

The mechanisms of energy transport by solid particles in a turbulent water channel flow were investigated by particle image velocimetry. A filtering technique, which is used in large eddy simulation, was applied to the fluid flow amongst particles to extract a characteristic length scale that governs the energy transfer from particles to fluid turbulence. The turbulence intensity in the streamwise direction, which is identical to the gravity direction, was strongly augmented by particles whose size is slightly greater than the Kolmogorov length scale. The directional scale dependency structure was observed, i.e., large eddies were dissipated in front of particles and particle wake generated eddies, which is emphasized when particles aligned perpendicular to the gravity direction. The subgrid scale turbulence energy is increased until Δ/η≈ 10 (Δ: filter width, η: kolmogorov length scale), which means that particles generate eddies whose size is less than 10 η. The energy backscatter in the presence of particles was observed at Δ/d_p≈5 (d_p : particle diameter), indicating that particles affect the eddy motion whose size is approximately five times particle diameter.