Experiments on two-layer density-stratified inertial gravity currents

Experiments on two-layer density-stratified inertial gravity currents Experiments for the gravity currents produced from a two-layer density-stratified buoyancy source in a full-depth, lock-exchange setup with a scaling analysis describing the flow morphologies are presented. In the inertial phase of propagation, the 3/2 power relationship xf3/2=1.5FIB01/2(t+tI) robustly applies between the front location xf and time t, where FI is the Froude number in the inertial phase, B0 is the total released buoyancy, and tI is the t-intercept. We showed that the Froude number in the inertial phase is not a universal constant but depends on the two controlling parameters, namely, the density difference ratio, Rρ=(ρU−ρ0)/(ρL−ρ0), where ρU,ρL, and ρ0 are the densities of the fluids in the upper layer, lower layer, and ambient environment, respectively, and the buoyancy distribution parameter, RB=BU/B0, where BU is the buoyancy in the upper layer. For a given buoyancy distribution parameter, the Froude number in the inertial phase decreases monotonically as the density difference ratio decreases. For a given density difference ratio, the Froude number in the inertial phase has a local minimum as the buoyancy distribution parameter falls in the range of 0.3≲RB≲0.5. When the buoyancy source is homogeneous, the Froude number in the inertial phase has its maximum value at FI=1.33±0.02. The flow morphology is also found to depend on the two controlling parameters. For weakly stratified two-layer heavy fluid, 0.4≲Rρ<1, mixing between the fluids from the two layers is more immediate. For strongly stratified two-layer heavy fluid, 0<Rρ≲0.4, there is less mixing between the layers for flows dominated by the upper layer, RB→1, and for flows dominated by the lower layer, RB→0. For gravity currents that are produced from a strongly stratified source and dominated by the upper layer, the upper layer may override and outrun the lower layer, which initially takes the lead after the two-layer heavy fluid is released. For gravity currents that are produced from a strongly stratified source and dominated by the lower layer, the lower layer may outrun the upper layer from the outset, resulting in streamwise stratification. Surprisingly, for the gravity currents produced from a strongly stratified source, mixing of fluids from the two layers can be enhanced when the buoyancy distribution parameter falls in the range of 0.3≲RB≲0.5. Such an exceptional observation is now successfully explained by the scaling analysis. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Physical Review Fluids American Physical Society (APS)

Experiments on two-layer density-stratified inertial gravity currents

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Experiments on two-layer density-stratified inertial gravity currents

Abstract

Experiments for the gravity currents produced from a two-layer density-stratified buoyancy source in a full-depth, lock-exchange setup with a scaling analysis describing the flow morphologies are presented. In the inertial phase of propagation, the 3/2 power relationship xf3/2=1.5FIB01/2(t+tI) robustly applies between the front location xf and time t, where FI is the Froude number in the inertial phase, B0 is the total released buoyancy, and tI is the t-intercept. We showed that the Froude number in the inertial phase is not a universal constant but depends on the two controlling parameters, namely, the density difference ratio, Rρ=(ρU−ρ0)/(ρL−ρ0), where ρU,ρL, and ρ0 are the densities of the fluids in the upper layer, lower layer, and ambient environment, respectively, and the buoyancy distribution parameter, RB=BU/B0, where BU is the buoyancy in the upper layer. For a given buoyancy distribution parameter, the Froude number in the inertial phase decreases monotonically as the density difference ratio decreases. For a given density difference ratio, the Froude number in the inertial phase has a local minimum as the buoyancy distribution parameter falls in the range of 0.3≲RB≲0.5. When the buoyancy source is homogeneous, the Froude number in the inertial phase has its maximum value at FI=1.33±0.02. The flow morphology is also found to depend on the two controlling parameters. For weakly stratified two-layer heavy fluid, 0.4≲Rρ<1, mixing between the fluids from the two layers is more immediate. For strongly stratified two-layer heavy fluid, 0<Rρ≲0.4, there is less mixing between the layers for flows dominated by the upper layer, RB→1, and for flows dominated by the lower layer, RB→0. For gravity currents that are produced from a strongly stratified source and dominated by the upper layer, the upper layer may override and outrun the lower layer, which initially takes the lead after the two-layer heavy fluid is released. For gravity currents that are produced from a strongly stratified source and dominated by the lower layer, the lower layer may outrun the upper layer from the outset, resulting in streamwise stratification. Surprisingly, for the gravity currents produced from a strongly stratified source, mixing of fluids from the two layers can be enhanced when the buoyancy distribution parameter falls in the range of 0.3≲RB≲0.5. Such an exceptional observation is now successfully explained by the scaling analysis.
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Publisher
The American Physical Society
Copyright
Copyright © ©2017 American Physical Society
eISSN
2469-990X
D.O.I.
10.1103/PhysRevFluids.2.073802
Publisher site
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Abstract

Experiments for the gravity currents produced from a two-layer density-stratified buoyancy source in a full-depth, lock-exchange setup with a scaling analysis describing the flow morphologies are presented. In the inertial phase of propagation, the 3/2 power relationship xf3/2=1.5FIB01/2(t+tI) robustly applies between the front location xf and time t, where FI is the Froude number in the inertial phase, B0 is the total released buoyancy, and tI is the t-intercept. We showed that the Froude number in the inertial phase is not a universal constant but depends on the two controlling parameters, namely, the density difference ratio, Rρ=(ρU−ρ0)/(ρL−ρ0), where ρU,ρL, and ρ0 are the densities of the fluids in the upper layer, lower layer, and ambient environment, respectively, and the buoyancy distribution parameter, RB=BU/B0, where BU is the buoyancy in the upper layer. For a given buoyancy distribution parameter, the Froude number in the inertial phase decreases monotonically as the density difference ratio decreases. For a given density difference ratio, the Froude number in the inertial phase has a local minimum as the buoyancy distribution parameter falls in the range of 0.3≲RB≲0.5. When the buoyancy source is homogeneous, the Froude number in the inertial phase has its maximum value at FI=1.33±0.02. The flow morphology is also found to depend on the two controlling parameters. For weakly stratified two-layer heavy fluid, 0.4≲Rρ<1, mixing between the fluids from the two layers is more immediate. For strongly stratified two-layer heavy fluid, 0<Rρ≲0.4, there is less mixing between the layers for flows dominated by the upper layer, RB→1, and for flows dominated by the lower layer, RB→0. For gravity currents that are produced from a strongly stratified source and dominated by the upper layer, the upper layer may override and outrun the lower layer, which initially takes the lead after the two-layer heavy fluid is released. For gravity currents that are produced from a strongly stratified source and dominated by the lower layer, the lower layer may outrun the upper layer from the outset, resulting in streamwise stratification. Surprisingly, for the gravity currents produced from a strongly stratified source, mixing of fluids from the two layers can be enhanced when the buoyancy distribution parameter falls in the range of 0.3≲RB≲0.5. Such an exceptional observation is now successfully explained by the scaling analysis.

Journal

Physical Review FluidsAmerican Physical Society (APS)

Published: Jul 26, 2017

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