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Abstract
Results from seven direct and large-eddy simulations of gravity currents on slopes ranging from 0.14 $^{\circ }$ to 2.86 $^{\circ }$ that span from the subcritical to the supercritical regime are studied. By considering a long domain, attention is focused on the near-self-similar state approached by these currents far downstream. In the self-similar limit, the various shape factors, local Richardson number, entrainment coefficient, velocity scale and basal drag coefficient reach a constant value, while the current height, volume and momentum fluxes continue to increase linearly. Their dependence on slope is presented.
Highlights
Ambient fluid entrainment is an important phenomenon that plays a key role in the dynamics of unbounded shear flows such as jets and plumes and bounded shear flows such as gravity currents
The incorporation of clear ambient fluid into the current is measured through the average vertical velocity in the far field, which can be modelled as the product of an entrainment coefficient and the velocity scale as we = −ewU
We focus on three important aspects that are of most relevance. (i) The interface with the ambient is highly turbulent in the supercritical current while it is very flat and non-turbulent in the subcritical current. (ii)In panels (d, f,h), two horizontal surfaces of zero turbulent production marked as z|P =0 are shown
Summary
Ambient fluid entrainment is an important phenomenon that plays a key role in the dynamics of unbounded shear flows such as jets and plumes and bounded shear flows such as gravity currents. In the near-self-similar state, while the thickness of the current continues to increase, the velocity scale becomes a constant Integral quantities such as Ri, ew and basal drag coefficient depend only on the slope S. At steeper slopes of S 0.05, the current evolves to a near-self-similar supercritical state, which is characterized by a turbulent near-wall layer close to the bottom boundary and a turbulent interface layer where the current vigorously mixes with the ambient (Salinas et al 2021a). At shallow slopes of S 0.01, the current evolves to a near-self-similar subcritical state, which is characterized by a turbulent near-wall layer but the interface layer remains turbulent-free without active mixing with the ambient.
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