Interwake turbulence properties of homogeneous dilute particle-laden flows

The properties of turbulence generated by uniform fluxes of monodisperse spherical particles moving through a uniform flowing gas were studied experimentally, emphasizing the properties of the region surrounding individual wake disturbances, i.e., the turbulent interwake region. Mean and fluctuating values, probability density functions, and energy spectra of streamwise and cross-stream velocities were measured within a counterflowing particle/air wind tunnel using particle wake discriminating laser velocimetry. Test conditions included nearly monodisperse glass spheres having diameters of 0.5-2.2 mm, particle Reynolds numbers of 106-990, mean particle spacings of 13-208 mm, particle volume fractions less than 0.003%, direct rates of dissipation of turbulence by particles less than 4%, and turbulence generation rates sufficient to yield streamwise relative turbulence intensities in the range 0.2-1.5%. The turbulent interwake region was homogeneous and nearly isotropic with probability density functions that are well approximated by Gaussian functions. Relative turbulence intensities were correlated effectively based on an analogy to the properties of isotropic grid-generated turbulence by scaling with the mean particle spacing normalized by the particle wake momentum diameter. For present turbulence generation conditions the turbulent interwake region had turbulence Reynolds numbers of 0.4-3.5 and was in the final decay period where vortical regions fill the turbulent interwake region but are sparse. This implies enhanced rates of dissipation of turbulent kinetic energy and decreasing macroscale/microscale ratios of the turbulence with increasing Reynolds numbers, as opposed to increasing ratios with increasing Reynolds numbers typical of conventional fully developed isotropic turbulence.