Author(s): Ching-Sen Wu; Albert Dai

Linked Author(s):

Keywords: Buoyancy-driven flows; Convection; Stratified flows and density currents

Abstract: Experiments on gravity currents produced from full-depth two-layer stratified buoyancy sources propagating in the slumping phase are presented in the paper. The Froude number in the slumping phase, F S = U f / g 0 ′ H , where U f is the front velocity, g 0 ′ is the average reduced gravity and H is the lock height, is influenced by the density difference ratio, R R = ( ρ U − ρ 0 ) / ( ρ L − ρ 0 ) , and the buoyancy distribution parameter, R B = B U / ( B L + B U ) , where ρ U , ρ L and ρ 0 are the fluid densities in the upper layer, lower layer and ambient environment while B U and B L represent the buoyancies in the upper layer and lower layer. The flow morphology of two-layer stratified gravity currents in the slumping phase can be categorized into two different regimes, demarcated by R B ≈ 0.6 . For R B 0.6 , the gravity currents are dominated by the lower layer and the lower layer takes the lead throughout the slumping phase. The Froude number in the slumping phase for R B 0.6 increases as R R decreases from unity. For R B > 0.6 , the gravity currents are dominated by the upper layer and the upper layer overrides and outruns the lower layer. The Froude number in the slumping phase for R B > 0.6 decreases as R R decreases from unity. As R B ≈ 0.6 , the upper layer and lower layer propagate forward approximately at the same speed and the Froude number in the slumping phase maintains at F S ≈ 0.46 irrespective of the density difference ratio. For weakly stratified two-layer buoyancy source, R R → 1 , the influence of the buoyancy distribution parameter diminishes and the Froude number in the slumping phase approaches F S ≈ 0.45 .

DOI: https://doi.org/10.1080/00221686.2019.1671517

Year: 2020