Journal article
Tail structure and bed friction velocity distribution of gravity currents propagating over an array of obstacles
Journal of fluid mechanics, Vol.694, pp.252-291
03/10/2012
DOI: 10.1017/jfm.2011.542
Abstract
The bed friction velocity distribution and sediment entrainment potential of Boussinesq compositional gravity currents propagating over a series of obstacles and over a smooth surface, respectively, are analysed based on high-resolution, three-dimensional large-eddy simulations. The investigation focuses on the parameter regime for which currents with a high volume of release go through an extended slumping phase with approximately constant front velocity (Tokyay, Constantinescu & Meiburg, J. Fluid Mech., vol. 672, 2011, 570–605). Under these conditions, a quasi-steady regime is reached between consecutive obstacles that is similar to the steady regime observed for constant-density channel flows over bottom obstacles. At a given location, this quasi-steady regime is reached in the tail of the current after the passage of the front and the associated hydraulic jumps reflected from the first few downstream obstacles. A double-averaging procedure is employed to characterize the global changes in the structure of the tail region between currents with a high volume of release propagating over smooth surfaces and over obstacles. Reynolds-number-induced scale effects on the flow and turbulence structure within the tail region are discussed in some detail. The presence of this quasi-steady regime is significant, since the simulations with obstacles show that most of the sediment is entrained by the tail of the current, rather than by its front. A detailed analysis of the effects of the obstacle shape on the quasi-steady mean flow and turbulence structure is presented, which provides insight into why gravity currents over dunes can entrain more sediment than gravity currents over ribs of comparable size. Finally, the bed friction velocity distributions and the potential to entrain sediment are compared for a compositional current with a high volume of release during the slumping phase, and a current with a low volume of release for which transition to the buoyancy–inertia phase occurs a short time after the release of the lock gate.
Details
- Title: Subtitle
- Tail structure and bed friction velocity distribution of gravity currents propagating over an array of obstacles
- Creators
- Talia Tokyay - 1Department of Civil and Environmental Engineering, IIHR-Hydroscience & Engineering, The University of Iowa, Iowa City, IA 52242, USAGeorge Constantinescu - 1Department of Civil and Environmental Engineering, IIHR-Hydroscience & Engineering, The University of Iowa, Iowa City, IA 52242, USAEckart Meiburg - 3Department of Mechanical Engineering, University of California at Santa Barbara, Santa Barbara, CA 93106-5070, USA
- Resource Type
- Journal article
- Publication Details
- Journal of fluid mechanics, Vol.694, pp.252-291
- Publisher
- Cambridge University Press; Cambridge, UK
- DOI
- 10.1017/jfm.2011.542
- ISSN
- 0022-1120
- eISSN
- 1469-7645
- Number of pages
- 40
- Language
- English
- Date published
- 03/10/2012
- Academic Unit
- Civil and Environmental Engineering
- Record Identifier
- 9983992034702771
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