Slope dependence of self-similar structure and entrainment in gravity currents

Gravity currents are flows driven by the action of gravity over fluids with different density. Here we focus on gravity currents where heavier fluid travels along the bottom of a sloping bed, underneath a large body of stagnant lighter ambient fluid. The thickness of the current increases due to entrainment of ambient fluid into the current. Direct numerical and large eddy simulations of gravity currents are performed, and a wall-jet transporting a passive scalar field. We focus on the rate of penetration of mean momentum and mean concentration of the agent responsible for the density difference (temperature, salinity, or sediment volume fraction) into the ambient fluid. The rates of penetration of turbulence-related quantities (i.e., turbulent kinetic energy, Reynolds flux and stress) into the ambient are analyzed. A robust methodology for defining the upper edge of these quantities and thereby define the current thickness using these different mean and turbulent quantities is presented. A comparison between downstream evolution of the gravity current with the corresponding behaviors of canonical wall-bounded turbulent flows is presented. The present understanding of turbulent/non-turbulent interface (TNTI) is extended to include subcritical flows where, due to the strong effect of stratification, the TNTI is buried well within the upper edge of the current and confined right above the inner near-bed layer. The present work sheds light on the striking difference between the different definitions of thickness (momentum, concentration, turbulence, etc.) in subcritical gravity currents, where stratification suppress turbulence in the upper region of the current.

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On the definition, evolution, and properties of the outer edge of gravity currents: A direct-numerical and large-eddy simulation study

Salinas

Balachandar

Zúñiga

et al. 2023

Physics of Fluids

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Planar wall plumes bounded by vertical and inclined surfaces

Zúñiga,

Balachandar,

Yang

et al. 2024

Physics of Fluids

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Planar wall plumes are gravity-driven flows where a fluid of lower (or higher) density than the ambient rises (or lowers) along a vertical or inclined wall. This study investigates planar wall plumes at five different wall slopes, ranging from a vertical wall (θ=90°) to a shallow inclination of θ=3°, using highly resolved direct numerical simulations. The three-dimensional turbulent structure of these supercritical flows is investigated in detail along with the streamwise evolution of the depth-averaged quantities. Simulations were performed in very large domains in order to focus attention on the behavior of the plumes in the near self-similar state, far downstream of the inlet. In the self-similar state, key quantities such as the entrainment rate, the basal drag coefficient, the Richardson number (or equivalently the Froude number), and the shape factors reach constant values, which dependent only on the slope. The present simulations, along with earlier results for subcritical currents at shallower slopes, provide a complete description of this dependency.

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Universal nature of rapid evolution of conservative gravity and turbidity currents perturbed from their self-similar state

et al. 2022

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Slope dependence of self-similar structure and entrainment in gravity currents

Cited by 5 publications

References 26 publications

On the definition, evolution, and properties of the outer edge of gravity currents: A direct-numerical and large-eddy simulation study

On the definition, evolution, and properties of the outer edge of gravity currents: A direct-numerical and large-eddy simulation study

Planar wall plumes bounded by vertical and inclined surfaces

Universal nature of rapid evolution of conservative gravity and turbidity currents perturbed from their self-similar state

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