David J. Goldfarb
Post-Doctoral Research Associate
Ph.D., Rutgers University, NJ, 2000
Exxon Research & Engineering Co.
Shear Instabilities in granular chute flow. (chute flow, granular PIV, Kelvin-Helmholtz instability)
Although shear instabilities have long been studied for fluid systems, the role of such instabilities in rapid granular shear flows is unclear. Specifically, the distinction between fluid and grain response to shear is poorly understood, and such instabilities have not been known to be observed at a "granular-granular" interface. The impact of an improved understanding of such instabilities is significant--academic and industrial enterprises alike increasingly need to process particles with higher reliability and control.Systematic studies of shear response in fluids have relied on paradigmatic experiments, e.g., past splitter plates, but these do not appear to exist in the granular literature. In granular chute flow experiments, we observe "crinkling" at the interface between different velocity granular flows downstream of a splitter plate. These sharp instabilities are accentuated for larger upstream differential velocities, and are highest at angles just slightly steeper than the angle of repose of the slower flow. We quantitatively study the development of such instabilities using image analysis and Particle Image Velocimetry techniques, and present a granular flow model which qualitatively agrees with our experimental data.