Zgheib, Nadim. Gravity currents from nonaxisymmetric releases. PhD, Institut National Polytechnique de Toulouse, 2015

(Document in English)
PDF  Requires a PDF viewer such as GSview, Xpdf or Adobe Acrobat Reader 6MB 
Official URL: http://ethesis.inptoulouse.fr/archive/00002988/
Abstract
Gravity currents are buoyancy driven flows that appear in a variety of situations in nature as well as industrial applications. Typical examples include avalanches, oil spills, and turbidity currents. Most naturally occurring gravity currents are catastrophic in nature, and therefore there is a need to understand how these currents advance, the speeds they can attain, and the range they might cover. This dissertation will focus on the short and long term evolution of gravity currents initiated from a finite release. In particular, we will focus attention to hitherto unaddressed effect of the initial shape on the dynamics of gravity currents. A range of parameters is considered, which include the density ratio between the current and the ambient (heavy, light, and Boussinesq currents), the initial height aspect ratio (height/radius), different initial crosssectional geometries (circular, rectangular, plusshaped), a wide range of Reynolds numbers covering 4 orders of magnitude, as well as conservative scalar and nonconservative (particledriven) currents. A large number of experiments have been conducted with the abovementioned parameters, some of these experiments were complemented with highlyresolved direct numerical simulations. The major outcome is that the shape of the spreading current, the speed of propagation, and the final deposition profile (for particledriven currents) are significantly influenced by the initial geometry, displaying substantial azimuthal variation. Especially for the rectangular cases, the current propagates farther and deposits more particles along the initial minor axis of the rectangular cross section. This behavior pertaining to nonaxisymmetric release is robust, in the sense that it is observed for the aforementioned range of parameters, but nonetheless cannot be predicted by current theoretical models such as the box model, which has been proven to work in the context of planar and axisymmetric releases. To that end, we put forth a simple analytical model (an extension to the classical box model), well suited for accurately capturing the evolution of finite volume gravity current releases with arbitrary initial shapes. We further investigate the dynamics of a gravity current resulting from a finite volume release on a sloping boundary where we observe some surprising features.
Item Type:  PhD Thesis 

Uncontrolled Keywords:  
Institution:  Université de Toulouse > Institut National Polytechnique de Toulouse  Toulouse INP (FRANCE) 
Laboratory name:  
Research Director:  Balachandar, Sivaramakrishnan and Bonometti, Thomas 
Statistics:  download 
Deposited On:  26 May 2015 21:58 
Repository Staff Only: item control page