Mixing in continuous gravity currents

Sher, Diana and Woods, Andrew W. (2017) Mixing in continuous gravity currents. Journal of Fluid Mechanics, 818. pp. 3710-3718. ISSN 0022-1120, ESSN: 1469-7645 DOI 10.1017/jfm.2017.168

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Abstract

We present measurements of the entrainment of ambient fluid into high-Reynolds-number gravity currents produced by a steady flux of buoyancy. The currents propagate along a horizontal channel and the mixing is measured using a light attenuation technique to obtain the cross-channel average of the density throughout the current. The total volume of the current increases linearly with time, at a rate in the range (1.8−2.1)Qo for source Froude numbers, Fro , in the range 0.1−3.7 , where Qo is the source volume flux per unit width. Most mixing occurs either immediately downstream of the inflow or near the head of the flow, with an increasing proportion of the entrainment occurring in a mixing zone near the inflow as Fro increases. A vertical gradient in the density and horizontal velocity develops in this mixing zone. This enables relatively dense fluid at the base of the current to catch up with the head, where it rises and mixes with the ambient fluid which is displaced over the head. The mixed fluid continues forward more slowly than the head, forming the relatively dilute fluid in the upper part of the current. Our data show that the depth and the depth-averaged buoyancy are primarily dependent on the position relative to the front, with the speed of the front being λ(Fro)B1/3o , where Bo is the source buoyancy flux per unit width. Here, λ(Fro) increases from 0.9 to 1.1 as Fro increases from 0.1 to 3.7, while the Froude number at the head of the flow has a value of 1.1±0.05 .

Item Type: Article
Uncontrolled Keywords: 2017AREP; IA72;
Subjects: 05 - Petrology - Igneous, Metamorphic and Volcanic Studies
Divisions: 05 - Petrology - Igneous, Metamorphic and Volcanic Studies
99 - Other
Journal or Publication Title: Journal of Fluid Mechanics
Volume: 818
Page Range: pp. 3710-3718
Identification Number: 10.1017/jfm.2017.168
Depositing User: Sarah Humbert
Date Deposited: 09 Jun 2017 11:29
Last Modified: 19 Jun 2017 10:20
URI: http://eprints.esc.cam.ac.uk/id/eprint/3981

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