Measurements and predictions of turbulence generation in homogeneous particle-laden flows

The overall properties of turbulence generated by uniform fluxes of monodisperse spherical particles moving through a uniform flowing gas were studied both theoretically and experimentally. Mean and fluctuating values, probability density functions and energy spectra of streamwise and cross-stream velocities were measured within a counter-flowing particle/air wind tunnel using laser velocimetry. Test conditions included nearly monodisperse glass spheres having diameters of 0.5, 1.1 and 2.2 mm, particle Reynolds numbers of 106, 373 and 990, mean particle spacings of 13-208 mm, particle volume fractions less than 0.003%, and direct rates of dissipation of turbulence by particles less than 4%. Velocity fluctuations and PDFs were predicted using volume fraction weighted conditional averages of the properties of the wake disturbances and the turbulent inter-wake region. The relative turbulence intensities were correlated with a dimensionless dissipation factor developed during a previous study of inter-wake turbulence. The PDFs of streamwise velocities were not Gaussian, with negative skewness and higher kurtosis than a Gaussian distribution due to the presence of wake disturbances. The measurements and predictions of the above properties agree with each other very well. Finally, the streamwise energy spectra demonstrate both -1 and -5/3 decay regions, with the former resulting from contributions due to the presence of the laminar-like turbulent wakes of particles.