Publication Date:
2019-10-07
Description:
We present experimental results on the development of gravity currents moving onto sloping boundaries with slope angles, and. Different regimes of flow development are observed depending on the slope angle and on the initial velocity and density profiles, characterized by the Richardson number, where, and are, respectively, the velocity interface thickness, the maximum velocity difference and reduced gravity at the beginning of the slope. For 0.7$]]〉 and the larger slope angle, the flow strongly accelerates, reaches a maximum at the beginning of the Kelvin-Helmholtz instability, then decelerates and re-accelerates again. For 〈![CDATA[$0.3〈J-{i}, instability occurs earlier and velocity oscillations are less. When the increase in velocity is smooth. The magnitude of velocity oscillation depends on the combined effect of and slope angle, expressed by an overall acceleration parameter, which, to first order, is given by, where and are, respectively, the velocity and position at instability onset. The velocity increases smoothly up to an equilibrium state when and exhibits an irregular behaviour at larger values of. The critical Richardson number decreases with increasing (increasing) which is due to wall effects and. After the beginning of Kelvin-Helmholtz instability, entrainment rates are close to those of a mixing layer, decreasing to values of a gravity current after the mixing layer reaches the boundary. It is shown here that the interfacial instability during current development affects the bottom shear stress which can reach values of regardless of initial conditions. By solving numerically the depth integrated governing equations, the gravity flow velocity, depth and buoyant acceleration in the flow direction can be well predicted for all the performed experiments over the full measurement domain. The numerical results for the experiments with 0.3$]]〉 predict that the current requires a distance of at least to reach a normal state of constant velocity, which is much larger than the distance required in the case of a current with that is commonly assumed for downslope currents. © 2019 Cambridge University Press.
Print ISSN:
0022-1120
Electronic ISSN:
1469-7645
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
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