Measurements of Velocity, Velocity Fluctuation, Density, and Stresses in Chute Flows of Granular Materials

Abstract

Experiments on continuous, steady flows of granular materials down an inclined channel or chute have been conducted with the objectives of understanding the characteristics of chute flows and of acquiring information on the rheological behavior of granular material flow. Two neighboring fiber-optic displacement probes provide a means to measure (1) the mean velocity by cross-correlating two signals from the probes, (2) the unsteady or random component of the particle velocity in the longitudinal direction by a procedure of identifying particles, and (3) the mean particle spacing at the boundaries by counting the frequency of passage of the particles. In addition, a strain-gauged plate built into the chute base has been employed to make direct measurement of shear stress at the base. With the help of these instruments, the vertical profiles of mean velocity, velocity fluctuation, and linear concentration were obtained at the sidewalls. Measurements of some basic flow properties such as solid fraction, velocity, shear rate, and velocity fluctuation were analyzed to understand the characteristics of the chute flow. Finally, the rheological behavior of granular materials was studied with the experimental data. In particular, the rheological models of Lun et al. (1984) for general flow and fully developed flow were compared with the present data.

Local measurements of velocity fluctuations and diffusion coefficients for a granular material flow

“…For all exit openings, it was observed that the corresponding mean flow speed was higher for the dyed particles than for the clear particles. The reason for this phenomenon is not clear, though it might be due to the exit hopper condition (Nguyen, Brennen & Sabersky 1979;Brennen & Pearce 1978). Figure 7 compares the normalized transverse fluctuation velocity distributions, at three representative transverse locations, for the rough and smooth wall conditions.…”

“…Although the granular temperature is a key property in the analytical studies, there have been few attempts to measure its magnitude in experimental studies. Ahn, Brennen & Sabersky (1991) and Hsiau & Hunt (1993a) only measured the streamwise fluctuation velocity 2 V. V. R. Natarajan, M. L. Hunt and E. D. Taylor component using fibre-optic probes. Drake (1991) measured both fluctuation velocity components in a two-dimensional, high-shear-rate low-density flow down an inclined chute, using high-speed photographic techniques.…”

Shallow granular flows down flat frictional channels: Steady flows and longitudinal vortices

“…However, most industrial conditions involve flat boundaries, as well as natural flows occurring on smooth bed rocks at the scale of the grains. Surprisingly very few studies [2,11,[25][26][27][28][29][30][31][32] have considered this more common case of flat frictional surfaces. Early experimental works mention increased flow velocity and sliding conditions at the boundaries compared to the bumpy walls case [11].…”

Monodisperse dry granular flows on inclined planes: Role of roughness

“…It is also common in geophysical situations where rock avalanches, landslides and pyroclastic and debris flows are natural events consisting in large-scale flows of grains [1,2,3]. Many chute flow experiments have been carried out and different configurations have been used, changing the boundary conditions from smooth [4,5] to rough [6], and using different kinds of materials [7,8,9,10] without any systematic investigation.…”