Measurements and Predictions of Turbulence Generation in Homogeneous Particle-laden Flows

Nomenclature The overall properties of turbulence c, = generated by uniform fluxes of monodisperse D = spherical particles moving through a uniform = flowing gas were studied both theoretically and t(k) = experimentally. Mean and fluctuating values, f = probability density functions and energy spectra of fr = streamwise and cross-stream velocities were measured within a counter-flowing particle/air f, = wind tunnel using laser velocimetry. Test = conditions included nearly monodisperse glass k = spheres having diameters of 0.5, 1.1 and 2.2 mm, L = particle Reynolds numbers of 106, 373 and 990, e = 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 lp = predicted using volume fraction weighted n” = conditional averages of the properties of the wake PDF = disturbances and the turbulent inter-wake region. Re = The relative turbulence intensities were correlated Re, = with a dimensionless dissipation factor developed during a previous study of inter-wake turbulence. r = The PDFs of streamwise velocities were not S = Gaussian, with negative skewness and higher S = 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 U = energy spectra demonstrate both -1 and -5/3 decay Cd = regions, with the former resulting from contributions due to the presence of the laminaruiw = like turbulent wakes of particles. iii, = particle drag coefficient dissipation factor, Eq. (18) particle diameter streamwise energy spectrum frequency ‘weighted average of wake passing frequencies wake volume fraction wave number, 27tls streamwise integral length scale wake length characteristic width of laminar-like wakes Kolmogorov length scale, (~~/a)“~ mean particle spacing, EZq. (1) particle number flux probability density function particle Reynolds number, d&,/v turbulence Reynolds number, Re, = hii ‘/v, radial distance in laminar-like wakes skewness of PDF distance in streamwise direction Kolmogorov time scale, (v/E)‘~ mean streamwise relative velocity of a particle streamwise gas velocity mean streamwise velocity defect in wakes streamwise inter-wake air velocity mean streamwise inter-wake air