Microgravity Segregation in Collisional Granular Shearing Flows

Abstract

This article concerns granular shearing flows in microgravity where segregation of grains by size or mass is driven by spatial gradients in the fluctuation energy of the grains.Experiments were conducted on NASA's microgravity aircraft with a shear cell shaped like a race track and containing a mixture of two types of spherical grains. A gradient of fluctuation energy was produced between the inner, energetic moving boundary driving collisions among the grains and the outer, more dissipative boundary at the periphery of the cell. The energetics were achieved by covering the two boundaries with bumps of appropriate size and spacing and by setting the distance between the flat side walls through which the flow was observed.The grain segregation and the corresponding velocity statistics were captured by a high-speed video camera and analyzed using computer vision software. The resulting profiles of particle mean and fluctuation velocities were compared with computer simulations of the entire experimental apparatus.

A three-phase mixture theory for particle size segregation in shallow granular free-surface flows

“…This is in agreement with the experiments of Vallance & Savage (2000), but it should be noted that segregation in other more energetic systems may occur in the absence of gravity due to spatial gradients in the energy of the granular velocity fluctuations (e.g. Louge et al 2000, Jenkins & Yoon 2001. If the relative density differenceρ changes sign, so that the particles are buoyant, the direction of segregation is reversed and normally graded layers will be formed sufficiently far downstream.…”

Studies of gas-particle interactions in a microgravity flow cell

“…For this project, the Glenn Research Center is modifying an instrument that we have used to investigate mechanisms of granular segregation in microgravity (Louge, et al, 1999). The instrument consists of a flow channel in the shape of a race track bounded by a stationary shell and a moving inner wall driven by a chain (Fig.…”

“…Consequently, measurements of the instantaneous particle velocities are sufficient to determine how interstitial air affects the fluctuating velocities of the spheres. For these measurements, we will employ an imaging technique that we have demonstrated in similar granular flows on the KC-135 microgravity aircraft (Louge, et al, 1999). There, a high speed video camera was used to observe a flowing binary mixture of grains through lateral windows and particle velocity statistics were extracted using computer tracking (Fig.…”

“…In an attempt to corroborate the theory, we add viscous drag to an existing molecular dynamic simulation of the entire cell, where grains are followed individually through successive collisions (Louge, et al, 1999). Because of the relatively large number of spheres in the cell, we do not employ the methods of Brady and Bossis (1988), Ladd (1990) or Mo and Sangani (1994).…”

“…In addition, the required microgravity time is determined by the number N f ≈ 10,000 of video frames necessary to compute accurate grain velocity fluctuation statistics (Louge, et al, 1999), following the establishment of a steady flow. Then, using Eq.…”