The Experts below are selected from a list of 15 Experts worldwide ranked by ideXlab platform
John K Eaton - One of the best experts on this subject based on the ideXlab platform.
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Particle response and turbulence modification in fully developed channel flow
Journal of Fluid Mechanics, 1994Co-Authors: J D Kulick, John R Fessler, John K EatonAbstract: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.
J D Kulick - One of the best experts on this subject based on the ideXlab platform.
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Particle response and turbulence modification in fully developed channel flow
Journal of Fluid Mechanics, 1994Co-Authors: J D Kulick, John R Fessler, John K EatonAbstract: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.
Jennifer S Curtis - One of the best experts on this subject based on the ideXlab platform.
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a numerical study of granular shear flows of rod like Particles using the discrete element method
Journal of Fluid Mechanics, 2012Co-Authors: Yu Guo, Carl Wassgren, William R Ketterhagen, Bruno C Hancock, B James, Jennifer S CurtisAbstract:The effect of Particle aspect ratio and surface geometry on granular flows is assessed by performing numerical simulations of rod-like Particles in simple shear flows using the discrete element method (DEM). The effect of Particle surface geometry is explored by adopting two types of Particles: glued-spheres Particles and true cylindrical Particles. The Particle aspect ratio varies from one to six. Compared to frictionless spherical Particles, smaller stresses are obtained for the glued-spheres and cylindrical Particle systems in dilute and moderately dense flows due to the loss of translational energy, which is partially converted to rotational energy, for the non-spherical Particles. For dilute granular flows of non-spherical Particles, stresses are primarily affected by the Particle aspect ratio rather than the surface geometry. As the Particle aspect ratio increases, the effective Particle projected area in the plane perpendicular to the flow direction increases, so that the probability of the occurrence of the Particle collisions increases, leading to a reduction in Particle Velocity Fluctuation and therefore a decrease in the stresses. Hence, a simple modification is made to the kinetic theory for granular flows to describe the stress tensors for dilute flows of non-spherical Particles by incorporating a normalized effective Particle projected area to account for the effect of Particle collision probability. For dense granular flows, the stresses depend on both the Particle aspect ratio and the surface geometry. Sharp stress increases at high solid volume fractions are observed for the glued-spheres Particles with large aspect ratios due to the bumpy surfaces, which impede the flow. However, smaller stresses are obtained for the true cylindrical Particles with large aspect ratios at high solid volume fractions. This trend is attributed to the combined effects of the smooth Particle surfaces and the Particle alignments such that the major/long axes of Particles are aligned in the flow direction. In addition, the apparent friction coefficient, defined as the ratio of shear to normal stresses, is found to decrease as the Particle aspect ratio increases and/or the Particle surface becomes smoother at high solid volume fractions.
John R Fessler - One of the best experts on this subject based on the ideXlab platform.
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Particle response and turbulence modification in fully developed channel flow
Journal of Fluid Mechanics, 1994Co-Authors: J D Kulick, John R Fessler, John K EatonAbstract: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.
Yu Guo - One of the best experts on this subject based on the ideXlab platform.
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a numerical study of granular shear flows of rod like Particles using the discrete element method
Journal of Fluid Mechanics, 2012Co-Authors: Yu Guo, Carl Wassgren, William R Ketterhagen, Bruno C Hancock, B James, Jennifer S CurtisAbstract:The effect of Particle aspect ratio and surface geometry on granular flows is assessed by performing numerical simulations of rod-like Particles in simple shear flows using the discrete element method (DEM). The effect of Particle surface geometry is explored by adopting two types of Particles: glued-spheres Particles and true cylindrical Particles. The Particle aspect ratio varies from one to six. Compared to frictionless spherical Particles, smaller stresses are obtained for the glued-spheres and cylindrical Particle systems in dilute and moderately dense flows due to the loss of translational energy, which is partially converted to rotational energy, for the non-spherical Particles. For dilute granular flows of non-spherical Particles, stresses are primarily affected by the Particle aspect ratio rather than the surface geometry. As the Particle aspect ratio increases, the effective Particle projected area in the plane perpendicular to the flow direction increases, so that the probability of the occurrence of the Particle collisions increases, leading to a reduction in Particle Velocity Fluctuation and therefore a decrease in the stresses. Hence, a simple modification is made to the kinetic theory for granular flows to describe the stress tensors for dilute flows of non-spherical Particles by incorporating a normalized effective Particle projected area to account for the effect of Particle collision probability. For dense granular flows, the stresses depend on both the Particle aspect ratio and the surface geometry. Sharp stress increases at high solid volume fractions are observed for the glued-spheres Particles with large aspect ratios due to the bumpy surfaces, which impede the flow. However, smaller stresses are obtained for the true cylindrical Particles with large aspect ratios at high solid volume fractions. This trend is attributed to the combined effects of the smooth Particle surfaces and the Particle alignments such that the major/long axes of Particles are aligned in the flow direction. In addition, the apparent friction coefficient, defined as the ratio of shear to normal stresses, is found to decrease as the Particle aspect ratio increases and/or the Particle surface becomes smoother at high solid volume fractions.