Density Distribution Effects on the Settling Dynamics of Nonspherical Inertial Particles at Intermediate Reynolds Numbers
Open Access
- Author:
- Angle, Brandon
- Graduate Program:
- Mechanical Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- June 27, 2019
- Committee Members:
- Matthew J Rau, Thesis Advisor/Co-Advisor
Margaret Louise Byron, Thesis Advisor/Co-Advisor
Robert Francis Kunz, Committee Member - Keywords:
- nonspherical
settling
intermediate Reynolds number
cylinder - Abstract:
- In natural sedimentation, many particles of interest are both large and nonspherical. Some common particle types (e.g. naturally occurring aggregates) do not have a uniform mass distribution. As a result, the centers of mass and buoyancy are not co-located, leading to complex settling dynamics. Here we investigated the orientation and terminal velocity of initially horizontal, freely falling cylinders, in which the mass distribution was either constant (uniform-density, UD) or bipartite, undergoing a step change halfway along the length (compound-density, CD). Cylinders had relatively low aspect ratios (1≤AR≤4), and fell at intermediate Reynolds numbers (of order 100). We recorded the velocity, orientation, and landing site of each cylinder in quiescent flow. Results showed significant differences between the settling characteristics of uniform- and. compound-density cylinders. For cylinders with AR=1, varying center of mass location (CD cylinders) led to a more predictable fall trajectory and orientation compared to UD cylinders. Varying the center of mass location for AR=2 cylinders resulted in two different settling modes, demarcated by a transitional Reynolds number regime. For AR=4 cylinders, varying the center of mass location did not produce as large an effect, but did lead to an angled settling trajectory with a pronounced off-horizontal orientation relative to the UD cylinders. All CD cylinders, regardless of aspect ratio, were biased to land on the side of the tank where the more-dense end of the cylinder was initially oriented. In general, cylinders with the smallest vertical projected area fell with the greatest terminal velocity; however, the mechanisms controlling orientation remain unclear. Our results have important implications for predicting the settling behavior of naturally-occurring particles, and lay the groundwork for further study of particles settling in complex flows such as turbulence. Given our results in still water, the net torque created by non-co-located center of mass and center of volume are likely to strongly impact particle motion in turbulence.