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Pulse propagation in gravity currents

Allen, P. A.; Dorrell, R. M.; Harlen, O. G.; Thomas, R. E.; McCaffrey, W. D.

Authors

P. A. Allen

O. G. Harlen

Dr Robert Thomas R.E.Thomas@hull.ac.uk
Senior Research Fellow in Geomorphology and Flood Risk

W. D. McCaffrey



Abstract

Real world gravity current flows rarely exist as a single discrete event, but are instead made up of multiple surges. This paper examines the propagation of surges as pulses in gravity currents. Using theoretical shallow-water modeling, we analyze the structure of pulsed flows created by the sequential release of two lock-boxes. The first release creates a gravity current, while the second creates a pulse that eventually propagates to the head of the first current. Two parameters determine the flow structure: the densimetric Froude number at the head of the current, Fr, and a dimensionless time between releases, tre. The shallow-water model enables the flow behavior to be mapped in (Fr, tre) space. Pulse speed depends on three critical characteristic curves: two that derive from the first release and correspond to a wavelike disturbance which reflects between the head of the current and the back of the lock-box and a third that originates from the second release and represents the region of the flow affected by the finite supply of source material. Pulses have non-negative acceleration until they intersect the third characteristic, after which they decelerate. Variations in pulse speed affect energy transfer and dissipation. Critically for lahars, landslides, and avalanches, pulsed flows may change from erosional to depositional, further affecting their dynamics. Gravity current hazard prediction models for such surge-prone flows may underpredict risk if they neglect internal flow dynamics.

Journal Article Type Article
Publication Date Jan 1, 2020
Journal Physics of Fluids
Print ISSN 1070-6631
Electronic ISSN 1089-7666
Publisher AIP Publishing
Peer Reviewed Peer Reviewed
Volume 32
Issue 1
Article Number 016603
APA6 Citation Allen, P. A., Dorrell, R. M., Harlen, O. G., Thomas, R. E., & McCaffrey, W. D. (2020). Pulse propagation in gravity currents. Physics of Fluids, 32(1), https://doi.org/10.1063/1.5130576
DOI https://doi.org/10.1063/1.5130576
Keywords Gravity currents; Equations of fluid dynamics; Fluid mechanics; Newtonian mechanics
Publisher URL https://aip.scitation.org/doi/10.1063/1.5130576
Additional Information Received: 2019-10-04; Accepted: 2019-12-10; Published: 2020-01-22
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