Scaling for lobe and cleft patterns in particle-laden gravity currents

Jackson, Andrew (2014) Scaling for lobe and cleft patterns in particle-laden gravity currents. PhD thesis, University of Nottingham.

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Abstract

Lobe and cleft patterns are frequently observed at the leading edge of gravity currents, including non-Boussinesq particle-laden currents such as powder snow avalanches. Despite the importance of the instability in driving air entrainment, little is known about its origin or the mechanisms behind its development. In this work we seek to gain a better understanding of these mechanisms from a laboratory scale model of powder snow avalanches using lightweight granular material.

The instability mechanisms in these flows appear to be a combination of those found in both homogeneous Boussinesq gravity currents and unsuspended granular flows, with the size of the granular particles playing a central role in determining the wavelength of the lobe and cleft pattern. When scaled by particle diameter a relationship between Froude number and the wavelength of the lobe and cleft pattern is found, where the wavelength increases monotonically with Froude number. This relationship, in addition to Particle Image Velocimetry analysis, provides evidence for the existence of pairs of counter-rotating vortices at the leading edge of these currents, which play a key role in the development of the lobe and cleft pattern.

The internal pressure of these flows is found to scale with the dynamics of the large vortex-like structure that is observed within the head of the current.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Turnbull, A.
Munro, R.
Keywords: Avalanches, granular materials, pattern formation (Physical sciences)
Subjects: Q Science > QC Physics
Faculties/Schools: UK Campuses > Faculty of Engineering > Department of Civil Engineering
Item ID: 14237
Depositing User: EP, Services
Date Deposited: 04 Nov 2014 14:41
Last Modified: 21 Sep 2016 06:30
URI: http://eprints.nottingham.ac.uk/id/eprint/14237

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