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Small-scale entrainment in inclined gravity currents
Maarten van Reeuwijk1, Dominik Krug2, Markus Holzner3
11Department of Civil and Environmental Engineering, Imperial College London, London, SW7 2AZ UK.
Environmental Fluid Mechanics (Dordrecht, Netherlands : 2001)
|January 31, 2020
Summary
Buoyancy significantly impacts turbulent entrainment at small scales. Direct numerical simulations reveal that interface velocity scales with Kolmogorov velocity, linking integral and small-scale entrainment for gravity currents and wall jets.
Area of Science:
- Fluid Dynamics
- Turbulence Research
- Computational Physics
Background:
- Turbulent entrainment is crucial in many geophysical and engineering flows.
- Understanding the small-scale dynamics of the turbulent/nonturbulent interface is key to accurate modeling.
- Buoyancy effects can significantly alter turbulent structures and entrainment rates.
Purpose of the Study:
- To investigate the influence of buoyancy on small-scale turbulent entrainment.
- To analyze the behavior of the turbulent/nonturbulent interface in buoyancy-driven flows.
- To connect integral entrainment coefficients with small-scale entrainment mechanisms.
Main Methods:
- Direct numerical simulation (DNS) of a gravity current and a wall jet.
- Identification of the turbulent/nonturbulent interface using enstrophy iso-levels.
- Analysis of relative enstrophy isosurface velocity and its scaling.
Main Results:
- The relative enstrophy isosurface velocity scales with the Kolmogorov velocity in the viscous superlayer for both flow types.
- A strong agreement was found between integral entrainment coefficients and small-scale entrainment estimates.
- Baroclinic torque contribution to interface velocity was found to be negligible.
Conclusions:
- Buoyancy's effect on entrainment is primarily due to reduced interface velocity relative to the integral velocity scale and decreased isosurface area.
- The findings provide insights into the fundamental mechanisms governing entrainment in stratified turbulent flows.
- DNS results offer a basis for improving large-eddy simulations and turbulence models.
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