Lock-release Experiments Research Articles

Gravity current analyzer for lock-release experiments

Analyzing gravity currents and stratified flows thoroughly is a time-consuming task, particularly in engineering and educational contexts. Despite the availability of numerous tools for studying stratified flows, there is currently no software dedicated to analyzing gravity currents, integrating flow characterization with theoretical and empirical analyses. This study introduces an open-source tool (Dyenamic), specifically designed for conducting in-depth analyses of gravity currents using a single recorded video. The software incorporates a particle image velocimetry routine to examine the velocity field of the gravity current and the sediment particle transport, offering essential physical indices and categorization based on existing literature. Data from modeling results and laboratory experiments are used to perform calibration, validation, and sensitivity analyzes. The findings demonstrate strong alignment with the existing gravity current literature, highlighting the effectiveness of the software in characterizing gravity currents. Dyenamic emerges as a robust, user-friendly, and versatile tool suitable for educational and research endeavors.

Validation of the low dissipation computational algorithm CABARET-MFSH for multilayer hydrostatic flows with a free surface on the lock-release experiments

The article presents the results of validation in lock-release experiments of a new low-dissipative multilayer hydrostatic model CABARET-MFSH. This model describes the dynamics of fluid with variable density and free surface. The computational algorithm of the new model is based on the method of hyperbolic decomposition, which presents of a multilayer structure in the form of separate layers interacting throughout interfaces. An explicit CABARET scheme is used to solve the system of hyperbolic equations in each layer. The scheme has a second order of approximation and is time reversible. Consequently, the scheme is initially non-dissipative. Besides, mass and momentum exchange between layers and filtering of flux variables are used to regularize the multilayer hydrostatic model, which introduces additional numerical dissipation into the scheme. The parameters of the filtering procedure are determined empirically from the condition of the stability of the algorithm and the minimal of the scheme viscosity. A 2D spatial version of our model is used for modeling lock-release experiments described in this article due to the uniformity of the current in the transverse direction. The results of numerical calculations are in satisfactory agreement with experimental data.

Hydrodynamics of weakly and strongly stratified two-layer lock-release gravity currents

A series of lock-release experiments are carried out to investigate the hydrodynamics of weakly and strongly stratified two-layer gravity currents (GC) on a flat bottom. A particle image velocimetry (PIV) system combined with an optical method is used to obtain the mixing process, front velocity, and velocity profiles of the two-layer GCs, focusing on the effect of the initial height ratio and lock aspect ratio. For a weakly stratified two-layer GC, the two layers mix thoroughly earlier with a higher initial height ratio and lock aspect ratio. A theoretical model is improved to predict the time that is necessary for the thorough mixing during the propagation of weakly stratified two-layer GCs. For a strongly stratified two-layer GC, a higher initial height ratio leads to a larger velocity of the upper layer because of the larger initial density difference, which results in a shorter time for the upper layer to outrun the lower layer. After the upper layer outruns the lower layer, the current has a constant-velocity phase and then a deceleration phase. The present investigation indicates that the maximum velocity in a vertical velocity profile of a strongly stratified two-layer GC is located at the position near to, or higher than the upper limit for single-layer GCs due to the smaller drag resistance at the upper boundary.

Gravity currents produced by lock-release: Theory and experiments concerning the effect of a free top in non-Boussinesq systems

We present an experimental and theoretical analysis of non-Boussinesq inertial (large Reynolds number flow) gravity currents (GCs) flowing in rectangular cross-sections. Attention is focused on the effects of the open upper boundary, which become pronounced when the density contrast between the current and the ambient is significant (non-Boussinesq case). The study is conducted deriving first a two-layer shallow-water (SW) model for the release of a constant fluid volume into an ambient of given height with a free-surface boundary condition, with an arbitrary density ratio r between the ambient and the intruding fluid. The jump conditions at the front are provided by the novel extension of Benjamin (1968) analysis , subject to energy-dissipation and sub-critical speed requests, as detailed in Ungarish (2017). The resulting SW lock-release problem is solved via a finite difference approach. Lock-release experiments are then conducted in this configuration with r=0.837−0.950, full-depth and part-depth locks, and two different lock lengths. Experimental results obtained for the front position and speed of the intruding current, its thickness, and the free-surface depression of the ambient fluid (a signature of these experiments marking the position of the intruding front) agree, to various degrees, with their theoretical counterparts, with a better agreement for the front position and depression than for the other quantities, but demonstrating in all cases the consistency of the trend. Some of the experiments were repeated with a top-lid boundary condition, to discern its effect on the current propagation. These effects turn out to be relatively minor except for the obvious absence of interface-height depression. The range of density ratio r examined is further extended by conducting a numerical simulations with r=0.7 using a numerical commercial Computational Fluid Dynamics code (CFD) based on Reynolds Averaged Navier-Stokes equations (RANS). A comparison among SW theory, experiments, and the numerical simulations is conducted in terms of the trough behind the current nose, leading to an overestimation of theoretical results with respect to experiments. The length of the through adequately scales with the lock-length.

Flow of buoyant granular materials along a free surface

We study experimentally the flow of light granular material along the free surface of a liquid of greater density. Despite a rich set of related geophysical and environmental phenomena, such as the spreading of calved ice, volcanic ash, debris and industrial wastes, there are few previous studies on this topic. We conduct a series of lock-release experiments of buoyant spherical beads into a rectangular tank initially filled with either fresh or salt water, and record the time evolution of the interface shape and the front location of the current of beads. We find that following the release of the lock the front location obeys a power-law behaviour during an intermediate time period before the nose of beads reaches a maximum runout distance within a finite time. We investigate the dependence of the scaling exponent and runout distance on the total amount of beads, the initial lock length, and the properties of the liquid that fills the tank in the experiments. Scaling arguments are provided to collapse the experimental data into universal curves, which can be used to describe the front dynamics of buoyant granular flows with different size and buoyancy effects and initial lock aspect ratios.

Non-self-similar viscous gravity currents

Lock-release experiments of viscous gravity currents (VGC) of glycerol released in water find different dynamics from air release. The current advance is nearly constant, then nearly halts as the head flattens, in contrast to known self-similar VGC where the front advances as a 1/5 power of time.

The propagation of particulate gravity currents in a V-shaped triangular cross section channel: Lock-release experiments and shallow-water numerical simulations

In this study, we investigate the motion of particulate gravity currents in a horizontal V-shaped channel. The particulate currents consisted of particles whose size varied between 0 and 100 μm but whose mean size increased. Particles were poorly sorted as the variance of the grain size distributions varied between 50 and 200. While the phases of propagation of homogeneous currents in such a geometry have been studied in the literature, this study considers the effects of the grain size on the propagation. The distance of propagation and front velocity of full-depth high-Reynolds-number lock-release experiments and shallow-water equation simulations were analyzed as the mean grain size of the initial particle distributions, defined by mass, was increased from 19 to 58 μm. Similar to the homogeneous currents, three consecutive phases of the front velocity could be identified but their characteristics and extent depend on the particle size. The initial phase, in particular, depends on a dimensionless settling number β that is defined as the ratio of two characteristic time scales, the propagation time x0/U, where U is the scale for the front speed and x0 the lock length, and the settling time h0/vs, where vs is the scale for the settling velocity and h0 the initial height of the current. For dimensionless settling numbers less than 0.001, the initial phase is characterized by a constant velocity for over about 6-7 lock lengths that is alike the initial slumping phase of perfectly constant velocity of the homogeneous currents. For dimensionless settling numbers greater than 0.001 and less than 0.015, the initial phase is no longer characterized by a constant velocity but an almost constant velocity for over about a similar 6-7 lock lengths. For dimensionless settling numbers greater than 0.015, however, as such, this phase is no longer seen. This initial phase is followed by a continuous decrease of the front advance, which results from the sedimentation of the particles. Unlike the homogeneous currents, this phase is a non-self-similar propagation. This phase is ended by a viscosity-dominated phase appearing to vary as ∼t1/7. The good agreement between the front advance of the experiments and shallow-water equation simulations demonstrates that the mean size by mass is a fairly good proxy of poorly sorted particles.

Gravity currents propagating up a slope

Bottom propagating gravity currents resulting from full- and partial-depth lock-release experiments are investigated as they approach and then propagate up a rising slope. Consistent with the prediction of a WKB-like theory, the gravity current front decelerates in a nearly uniform manner along the slope as 0.112g′s(D/H)(2 − D/H), in which g′ is the reduced gravity, s is the slope, D is the initial lock-fluid height, and H is the ambient fluid height. The shape of the gravity current as it decelerates over relatively steep slopes is found to be self similar with a nearly linear decrease of the head height between the start of the slope and up to 80% of the distance to the nose. Some deviation from self-similar behaviour is found in cases with small s because of the comparatively large volume of fluid in the gravity current tail that flows downslope while the front continues to advance upwards.

On gravity currents in a linearly stratified ambient: a generalization of Benjamin's steady-state propagation results

This paper presents a generalization of the classical results of T. B. Benjamin (J. Fluid. Mech. vol. 31, 1968, p. 209) concerning the propagation of a steady gravity current into a homogeneous ambient, to the case of a stratified ambient. The current of thickness ), mostly in the subcritical regime. Considerations for the physical acceptability of the multiple results are presented, and the connection with observations from lock-release experiments are discussed. The conclusion is that the present results provide a reliable and versatile generalization of the classical unstratified problem.

Nonhydraulic Effects in Particle‐Driven Gravity Currents in Deep Surroundings

In this article, we present an approach to modeling the flow of particle‐driven gravity currents produced by the sudden release of well‐mixed, fixed‐volume suspensions into deep surroundings. Our model accounts for the initial turbulent energy of mixing in the release volume, characteristic of the classical lock–release experiments, as well as the spatiotemporal variability in the driving buoyancy forces attributable to particle settling. We show that, in contrast to compositionally driven flows, particle‐driven flows cannot be described consistently in terms of shallow water theory. Specifically, we show that the presence of particles in the flow dynamics produces significant horizontal velocity shear, thereby changing the flow configuration in important ways from flows assumed to be governed by the shallow water equations. These new flow properties are calculated and contrasted with flow properties derived on the basis of the shallow water equations to show that the shallow water analysis misses dynamical features of the flow. We also show that our model provides significant improvement over the previous shallow water‐based models in predicting the experimentally determined deposition patterns associated with the lock–release experiments.

Fluid-particle Coupling In DiluteSuspension Releases

In this paper we shall present consistent scaling arguments leading to the development of various distinguished limit models for the study of particle suspension flows as produced in the classic lock-release experiments that are designed to illuminate the mechanisms of rarely observed submarine turbidity currents. We shall show that very dilute suspensions lead to a decoupling of fluid and particle dynamics and allow for a consistent description in terms of two-layer, shallow-water (hydraulic) theory, Moodie et aL [I] and Moodie [2], This class of models, when applied to the study of particle transport and deposition from bottom gravity currents produced by the sudden release of dilute, well-mixed fixed-volume suspensions have been relatively successful in predicting the experimentally observed longtime, distal, areal density of the deposit on a rigid horizontal bottom. These models, however, fail in their ability to capture the experimentally observed proximal pattern of the areal density with its pronounced dip in the region initially occupied by the well-mixed suspension and its equally pronounced local maximum at roughly the one third point of the total reach of the deposit in many experiments. We shall here show how to modify the assumptions of Moodie et al. [1] and Bonnecaze et al. [3,4,5] to account for the presence of initial turbulent energy of mixing in the release volume and thereby obtain better agreement with experimental results. We shall also outline an approach for relaxing the severe constraint on the dilute nature of these suspensions. Advances in Fluid Mechanics III, C.A. Brebbia & M. Rahman (Editors) © 2000 WIT Press, www.witpress.com, ISBN 1-85312-813-9