Turbulence attenuation in a particle-laden channel flow

Previous investigations of particle-laden flows have demonstrated that loadings of small, dense particles in gas flows can greatly attenuate the fluid turbulence levels. However, information about the small-scale turbulence structure of these flows is lacking and the underlying physical mechanisms responsible for the turbulence attenuation are not well understood. The objective of this research was to investigate experimentally the smallest scales of attenuated turbulence in a particle-laden channel flow.; Experiments were conducted in a vertical, fully-developed air channel flow at a Reynolds number of 13,800. The flow was seeded with two classes of monodisperse, spherical particles each with large Stokes numbers and diameters smaller than the dissipative scales of the turbulence. The 150 micron glass and 70 micron copper particles possessed similar particle time constants but achieved average particle Reynolds numbers of 18 and 8, respectively. The particles were loaded into the channel such that they constituted a negligible volume fraction but a significant mass fraction of the flow. A high spatial resolution particle image velocimetry (PIV) system was developed to interrogate small regions of the particle-laden turbulence field and acquire velocity statistics for both phases.; Moderate mass loadings of the particles (30–40%) were observed to decrease levels of the gas-phase turbulent kinetic energy and viscous dissipation rate by as much as 85% at the centerline of the channel. The extra dissipation of turbulent kinetic energy by particles was found to be small compared to the viscous dissipation rate. The particle Reynolds number was revealed to be an important parameter for turbulence attenuation with the glass particles inducing greater levels of turbulence attenuation than the copper particles at identical particle mass loadings. Two-point velocity correlations indicated that the streamwise length scales of the gas-phase turbulence increased relative to the spanwise scales as particle mass loadings were increased. Near-wall measurements showed that the Reynolds shear stress of the gas-phase was attenuated and indicated a decrease in the production of turbulent kinetic energy. It was concluded that modifications of the gas-phase turbulence structure by particles is a significant mechanism for turbulence attenuation in a particle-laden channel flow.