Particle response and turbulence modification in fully developed channel flow

Abstract

The interactions between small dense particles and fluid turbulence have been investigated in a downflow fully developed channel in air. Particle velocities of, and fluid velocities in the presence of, 50 μm glass, 90 μm glass and 70 μm copper spherical beads were measured by laser Doppler anemometry, at particle mass loadings up to 80%. These particles were smaller than the Kolmogorov lengthscale of the flow and could respond to some but not all of the scales of turbulent motion. Streamwise mean particle velocity profiles were flatter than the mean fluid velocity profile, which was unmodified by particle loading. Particle velocity fluctuation intensities were larger than the unladen-fluid turbulence intensity in the streamwise direction but were smaller in the transverse direction. Fluid turbulence was attenuated by the addition of particles; the degree of attenuation increased with particle Stokes number, particle mass loading and distance from the wall. Turbulence was more strongly attenuated in the transverse than in the streamwise direction, because the turbulence energy is at higher frequencies in the transverse direction. Streamwise turbulence attenuation displayed a range of preferred frequencies where attenuation was strongest.

Particle-resolved direct numerical simulation of homogeneous isotropic turbulence modified by small fixed spheres

“…The phenomenon has been observed experimentally in pipe flows (Tsuji et al 1984), channel flows (Kulick, Fessler & Eaton 1994;Kussin & Sommerfeld 2002) and stationary homogeneous turbulence (Hwang & Eaton 2006;Tanaka & Eaton 2010). These works clearly show that the turbulence kinetic energy of the carrier phase of a turbulent flow laden with small particles is lower than in the corresponding unladen flow.…”

“…Kulick et al (1994) measured strong turbulence attenuation in a gas-solid turbulent channel flow with a particle volume fraction of 0.0001, particle size d + p = 2.3 and Re τ = 640. Recently, a point-particle DNS of this case was performed in a configuration that contained roughly 10 5 particles (Vreman 2015).…”

“…Thus, it is surprising that the simulated attenuation of K is not much larger than 9 % and that the dissipation is not reduced. According to experiments, the degree of turbulence attenuation tends to increase with Stokes number (Kulick et al 1994;Tanaka & Eaton 2010). Larger Stokes number usually implies a weaker response of the motion of the particles to the fluid and a larger particle-fluid slip velocity.…”

Direct numerical simulation of a confined three-dimensional gas mixing layer with one evaporating hydrocarbon-droplet-laden stream

“…Gore & Crowe (1989) compiled results from a variety of experiments which suggest that solid particles can act either to dissipate or to enhance turbulence energy depending on the diameter of the particles relative to the integral lengthscale of the flow; however, no conclusions could be drawn as to the magnitude of the modulation. Kulick, Fessler & Eaton (1994) conducted experiments of a fully developed channel flow with solid particle mass loadings as large as 80%. It was observed that the fluid turbulence intensity was attenuated by the particles; however, the mean fluid velocity profile remained essentially unaltered for all cases.…”

Fluid–particle correlated motion and turbulent energy transfer in a two-dimensional particle-laden shear flow

“…They also found an increased isotropy of the velocity fluctuations of the water flow and from that concluded that the presence of the particles modifies the dynamics of the fluid turbulence, not only by exchange of momentum and energy, but also due to a possible influence of the particles on the flow structure. Kulick et al (1994) measured turbulence modification by 50 and 90 μm glass beads and 70 μm copper particles in a pipe flow and found that the copper particles reduced the carrier phase turbulence levels while the glass beads had little effect. Fessler & Eaton (1999) performed similar measurements in a backward facing step and found that turbulence reduction was a function of particle Stokes and Reynolds number and the specific flow regime.…”