Results are presented from a series of experiments investigating the internal and near-bed dynami... more Results are presented from a series of experiments investigating the internal and near-bed dynamics of restricted net exchange flows across a submerged sill obstruction. Experimental measurements focused on obtaining high-resolution velocity and density profiles in the vicinity of the obstruction to observe and quantify both interfacial mixing and boundary layer processes under a range of parametric forcing conditions (i.e. variable saline and fresh water flow rates; density differences; water levels). Detailed synoptic velocity fields were also measured across the obstruction through particle image velocimetry (PIV) to aid qualitative and quantitative interpretation of these internal and near-bed flow processes, with a focus on defining the specific parametric conditions under which saline intrusions could become arrested through erosion of the intrusion nose at the bed boundary by the freshwater outflow layer. In this regard, it is anticipated that the study findings will provide ...
Proceedings of the Institution of Civil Engineers - Engineering and Computational Mechanics
Analytical results from internal hydraulic theory are presented for a horizontal channel connecti... more Analytical results from internal hydraulic theory are presented for a horizontal channel connecting river- and sea-basin waters of slightly different densities. The maximal exchange of inviscid, two-layer flow is analysed for such a system, for the case of a non-rectangular channel. The internal hydraulic theory has been extended to include internal energy losses and related net barotropic flow components in the surface layer. The hydraulic model is tested using archival field measurements in the Pärnu River mouth, where stratified bi-directional flow, accompanied by variable sea-level conditions and river water discharges, was observed. The study demonstrates that internal hydraulic theory predicts satisfactorily the stratified bi-directional fluxes and density-interface depths observed in the river mouth. In this study the two-layer exchange problem is solved with two control points, but the theory can be applied quite generally to predict the layer depths of the river and marine ...
Environmental and geophysical flows, including dense bottom gravity currents in the ocean and buo... more Environmental and geophysical flows, including dense bottom gravity currents in the ocean and buoyancy-driven exchange flows in marginal seas,<br> are strongly controlled by topographic features.<br> These are known to exert significant influence on both internal mixing and secondary circulations generated by these flows.<br> In such cases, uni-directional or bi-directional exchange flows develop when horizontal density differences<br> and/or pressure gradients are present between adjacent water bodies connected by a submerged channel.<br> The flow dynamics of the dense lower layer depend primarily on the volumetric flux and channel cross-sectional shape,<br> while the stratified interfacial flow mixing characteristics, leading to fluid entrainment/detrainment,<br> are also dependent on the buoyancy flux and motion within the upper (lower density) water mass.<br> For submerged channels that are relatively wide compared to the internal ...
Preliminary analysis of a series of large-scale experiments investigating bi-directional stratifi... more Preliminary analysis of a series of large-scale experiments investigating bi-directional stratified flows across a submerged trapezoidal sill obstruction is presented. A range of parametric forcing conditions: i) variable fresh-and saltwater flow rates; ii) density differences; and iii) sill submergence depths are used to generate net-barotropic exchange flows. Detailed synoptic velocity fields are measured across the sill crest using PIV, while high-resolution density profiles are obtained using micro-conductivity probes sited at several channel and sill locations. These measurements are used to determine a relationship between the locations of i) the density excess 0.5-isopycnal interface, separating the intruding saline water from the overlying freshwater layer, and ii) the zero-velocity interface, defined by the reversal point of velocity profiles. Blockage of saline intrusions by strongly barotropic flows in the upper freshwater layer is detected under specific parametric combi...
Experimental study on dynamical blocking conditions of net exchange flows Janek Laanearu (1), Ala... more Experimental study on dynamical blocking conditions of net exchange flows Janek Laanearu (1), Alan Cuthbertson (2), Magda Carr (3), Joel Sommeria (4), Madis-Jaak Lilover (5), Samuel Viboud (4) and Jarle Berntsen (6) (1) Department of Mechanics, Tallinn University of Technology, Tallinn, Estonia, e-mail: janek.laanearu@ttu.ee (2) School of Energy, Geosciences, Infrastructure and Society, Heriot Watt University, Edinburgh, UK, e-mail: a.cuthbertson@hw.ac.uk (3) School of Mathematics, University of St Andrews, St Andrews, UK, e-mail: magda@mcs.st.uk (4) Laboratoire des Ecoulements Geophysiques et Industriels, Grenoble, France, email: joel.sommeria@legi.grenoble-inp.fr (5) Institute of Marine Systems, Tallinn University of Technology, Tallinn, Estonia, email: madis-jaak.lilover@msi.ttu.sea.ee (6) Department of Mathematics, University of Bergen, Bergen, Norway, email: jarleb@math.uib.no.ac.uk Abstract Preliminary analysis of a series of large-scale experiments investigating bi-directiona...
Results are presented from a series of large-scale experiments investigating the internal dynamic... more Results are presented from a series of large-scale experiments investigating the internal dynamics of bi-directional exchange flows generated across a submerged, trapezoidal, sill obstruction, with net-barotropic flow components in the upper fresh or lower saline water layers. High-resolution velocity fields and density profiles were obtained using particle image velocimetry and micro-conductivity probes, respectively, in the vicinity of the obstruction to measure internal-flow dynamics under a range of parametric forcing conditions (i.e. variable saline and fresh water volume fluxes; density differences; sill obstruction submergence depths). These measurements provided qualitative and quantitative interpretation of mixing and entrainment processes generated by the bi-directional exchange flows, as well as defining the parametric conditions under which the lower saline intrusion layer became blocked across the sill. An analytical two-layer hydraulic exchange flow model was developed...
Results are presented from a series of experiments investigating the internal and near-bed dynami... more Results are presented from a series of experiments investigating the internal and near-bed dynamics of restricted net exchange flows across a submerged sill obstruction. Experimental measurements focused on obtaining high-resolution velocity and density profiles in the vicinity of the obstruction to observe and quantify both interfacial mixing and boundary layer processes under a range of parametric forcing conditions (i.e. variable saline and fresh water flow rates; density differences; water levels). Detailed synoptic velocity fields were also measured across the obstruction through particle image velocimetry (PIV) to aid qualitative and quantitative interpretation of these internal and near-bed flow processes, with a focus on defining the specific parametric conditions under which saline intrusions could become arrested through erosion of the intrusion nose at the bed boundary by the freshwater outflow layer. In this regard, it is anticipated that the study findings will provide ...
Proceedings of the Institution of Civil Engineers - Engineering and Computational Mechanics
Analytical results from internal hydraulic theory are presented for a horizontal channel connecti... more Analytical results from internal hydraulic theory are presented for a horizontal channel connecting river- and sea-basin waters of slightly different densities. The maximal exchange of inviscid, two-layer flow is analysed for such a system, for the case of a non-rectangular channel. The internal hydraulic theory has been extended to include internal energy losses and related net barotropic flow components in the surface layer. The hydraulic model is tested using archival field measurements in the Pärnu River mouth, where stratified bi-directional flow, accompanied by variable sea-level conditions and river water discharges, was observed. The study demonstrates that internal hydraulic theory predicts satisfactorily the stratified bi-directional fluxes and density-interface depths observed in the river mouth. In this study the two-layer exchange problem is solved with two control points, but the theory can be applied quite generally to predict the layer depths of the river and marine ...
Environmental and geophysical flows, including dense bottom gravity currents in the ocean and buo... more Environmental and geophysical flows, including dense bottom gravity currents in the ocean and buoyancy-driven exchange flows in marginal seas,<br> are strongly controlled by topographic features.<br> These are known to exert significant influence on both internal mixing and secondary circulations generated by these flows.<br> In such cases, uni-directional or bi-directional exchange flows develop when horizontal density differences<br> and/or pressure gradients are present between adjacent water bodies connected by a submerged channel.<br> The flow dynamics of the dense lower layer depend primarily on the volumetric flux and channel cross-sectional shape,<br> while the stratified interfacial flow mixing characteristics, leading to fluid entrainment/detrainment,<br> are also dependent on the buoyancy flux and motion within the upper (lower density) water mass.<br> For submerged channels that are relatively wide compared to the internal ...
Preliminary analysis of a series of large-scale experiments investigating bi-directional stratifi... more Preliminary analysis of a series of large-scale experiments investigating bi-directional stratified flows across a submerged trapezoidal sill obstruction is presented. A range of parametric forcing conditions: i) variable fresh-and saltwater flow rates; ii) density differences; and iii) sill submergence depths are used to generate net-barotropic exchange flows. Detailed synoptic velocity fields are measured across the sill crest using PIV, while high-resolution density profiles are obtained using micro-conductivity probes sited at several channel and sill locations. These measurements are used to determine a relationship between the locations of i) the density excess 0.5-isopycnal interface, separating the intruding saline water from the overlying freshwater layer, and ii) the zero-velocity interface, defined by the reversal point of velocity profiles. Blockage of saline intrusions by strongly barotropic flows in the upper freshwater layer is detected under specific parametric combi...
Experimental study on dynamical blocking conditions of net exchange flows Janek Laanearu (1), Ala... more Experimental study on dynamical blocking conditions of net exchange flows Janek Laanearu (1), Alan Cuthbertson (2), Magda Carr (3), Joel Sommeria (4), Madis-Jaak Lilover (5), Samuel Viboud (4) and Jarle Berntsen (6) (1) Department of Mechanics, Tallinn University of Technology, Tallinn, Estonia, e-mail: janek.laanearu@ttu.ee (2) School of Energy, Geosciences, Infrastructure and Society, Heriot Watt University, Edinburgh, UK, e-mail: a.cuthbertson@hw.ac.uk (3) School of Mathematics, University of St Andrews, St Andrews, UK, e-mail: magda@mcs.st.uk (4) Laboratoire des Ecoulements Geophysiques et Industriels, Grenoble, France, email: joel.sommeria@legi.grenoble-inp.fr (5) Institute of Marine Systems, Tallinn University of Technology, Tallinn, Estonia, email: madis-jaak.lilover@msi.ttu.sea.ee (6) Department of Mathematics, University of Bergen, Bergen, Norway, email: jarleb@math.uib.no.ac.uk Abstract Preliminary analysis of a series of large-scale experiments investigating bi-directiona...
Results are presented from a series of large-scale experiments investigating the internal dynamic... more Results are presented from a series of large-scale experiments investigating the internal dynamics of bi-directional exchange flows generated across a submerged, trapezoidal, sill obstruction, with net-barotropic flow components in the upper fresh or lower saline water layers. High-resolution velocity fields and density profiles were obtained using particle image velocimetry and micro-conductivity probes, respectively, in the vicinity of the obstruction to measure internal-flow dynamics under a range of parametric forcing conditions (i.e. variable saline and fresh water volume fluxes; density differences; sill obstruction submergence depths). These measurements provided qualitative and quantitative interpretation of mixing and entrainment processes generated by the bi-directional exchange flows, as well as defining the parametric conditions under which the lower saline intrusion layer became blocked across the sill. An analytical two-layer hydraulic exchange flow model was developed...
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