Effect of particle size on modulating turbulent intensity

Particles-turbulence interaction

A condensed review of recent advances accomplished in the development and the applications of noninvasive tomographic and velocimetric measurement techniques to multiphase flows and systems is presented. In recent years utilization of such noninvasive techniques has become widespread in many engineering disciplines that deal with systems involving two immiscible phases or more. Tomography provides concentration, holdup, or 2D or 3D density distribution of at least one component of the multiphase system, whereas velocimetry provides the dynamic features of the phase of interest such as the flow pattern, the velocity field, the 2D or 3D instantaneous movements, etc. The following review is divided into two parts. The first part summarizes progress and developments in flow imaging techniques using γ-ray and X-ray transmission tomography; X-ray radiography; neutron transmission tomography and radiography; positron emission tomography; X-ray diffraction tomography; nuclear magnetic resonance imaging; electrica...

Noninvasive Tomographic and Velocimetric Monitoring of Multiphase Flows

On Models for Turbulence Modulation in Fluid-Particle Flows

This paper presents the results of a numerical investigation of the effects of near‐neutral density solid particles on turbulent liquid flow in a channel. Interactions of particles, in a size range about the dissipative length scale, with wall turbulence have been simulated at low volume fractions (average volume fraction less than 4×10−4). Fluid motion is calculated by directly solving the Navier‐Stokes equations by a pseudo‐spectral method and resolving all scales of motion. Particles are moved in a Lagrangian frame through the action of forces imposed by the fluid and gravity. Particle effects on fluid motion are fed back at each time step by calculating the velocity disturbance caused by the particles assuming the flow around them is locally Stokesian. Particle‐particle interactions are not considered. The slightly heavier‐than‐fluid particles of the size range considered are found to preferentially accumulate in the low‐speed streaks, as reported in several other investigations. It is also found that particles smaller than the dissipative length scale reduce turbulence intensities and Reynolds stress, whereas particles that are somewhat larger increase intensities and stress. By examining higher order turbulence statistics and doing a quadrant analysis of the Reynolds stress, it is found that the ejection‐sweep cycle is affected—primarily through suppression of sweeps by the smaller particles and enhancement of sweep activity by the larger particles. A preliminary assessment of the impact of these findings on scalar transfer is made, as enhancement of transfer rate is a motivation of the overall work on this subject. For the case investigated, comparison of the calculations with an existing experiment was possible, and shows good agreement.

R. Zisselmar

Papers

Investigation of solid—liquid pipe flow with regard to turbulence modification