Experimental study of uni and bi-directional exchange flows in a large scale rotating trapezoidal channel

International audienceA large-scale experimental study has been conducted at the Coriolis Rotating Platform to investigate the dynamics of uni- and bi-directional exchange flows along a channel with a trapezoidal cross section under the influence of background rotation. High-resolution two-dimensional particle image velocimetry and micro-conductivity probes were used to obtain detailed velocity fields and density profiles of the exchange flow generated across the channel under different parametric conditions. Experimental measurements give new insight into the stratified-flow dynamics dependence on the magnitude of Burger number, defined as the ratio of the Rossby radius to the channel width, such that values lower than 0.5 characterize unsteady exchange flows. The measurements highlight the role that both ambient rotation and net-barotropic forcing have on the geostrophic adjustment of the dense outflowing layer and on the corresponding counter-flowing water layer fluxes. The coupled effect of these two parametric conditions largely affects the transverse velocity distribution and, for the largest net-barotropic flow in the upper fresh water layer, leads to the partial blockage of the lower saline outflow. Moreover, an increase in the mixing layer thickness, associated with larger rotation rates, and due the interface dynamics, is observed, with shear-driven interfacial instabilities analyzed to highlight the influence of both ambient rotation and net-barotropic forcin

The dynamics of bi-directional exchange flows

The global demand for low carbon electricity requires a variety of energy generation approaches, the choice of which is dependent on multiple criteria. Tidal flows have long been identified as a reliable source of energy, with a high degree of predictability. To this end a novel turbine has been developed that could be well suited to energy generation in both tidal flows, or water courses. In this study a Smoothed Particle Hydrodynamics (SPH) model, namely DualSPHysics, is used to predict the behavior of this novel turbine design. Which will be used to guide the design process. The SPH method was chosen as the design of the turbine uses several connected parts, that requires free movement and interactions to properly represent the prototype and was found to be capable of expressing this behavior

The dynamics of bi-directional exchange flows::implication for morphodynamic change within estuaries and sea straits

Environmental and geophysical flows, including dense bottom gravity currents in the ocean and buoyancy-driven exchange flows in marginal seas, are strongly controlled by topographic features. These are known to exert significant influence on both internal mixing and secondary circulations generated by these flows. In such cases, uni-directional or bi-directional exchange flows develop when horizontal density differences and/or pressure gradients are present between adjacent water bodies connected by a submerged channel. The flow dynamics of the dense lower layer depend primarily on the volumetric flux and channel cross-sectional shape, while the stratified interfacial flow mixing characteristics, leading to fluid entrainment/detrainment, are also dependent on the buoyancy flux and motion within the upper (lower density) water mass. For submerged channels that are relatively wide compared to the internal Rossby radius of deformation, Earth rotation effects introduce geostrophic adjustment of these internal fluid motions, which can suppress turbulent mixing generated at the interface and result in the development of Ekman layers that induce secondary, cross-channel circulations, even within straight channels. Moreover, recent studies of dense, gravity currents generated in rotating and non-rotating systems, respectively, indicated that the V-shaped channel topography had a strong influence on both flow distribution and associated interfacial mixing characteristics along the channel. However, such topographic controls on the interfacial mixing and secondary circulations generated by bi-directional exchange flows are not yet fully understood and remain to be investigated thoroughly in the laboratory. Also the effect of mobile bed for bi-directional exchange flows generated in deformable channels along with the physical interactions between the lower dense water flow and the erodible bed sediments will have a strong influence in (re-)shaping the overall channel bed topography (i.e. bed morphodynamics). Consequently, the resulting temporal changes in cross-sectional channel bathymetry (i.e. through erosion and deposition processes) would also be expected to have associated feedbacks on transverse asymmetries in the bi-directional exchange flow structure, as well as on the internal flow stability

Applications in Water Systems Management and Modeling

With the growth of urbanization, industrialization, and intensive agricultural practices, all superficial, inland, and marine water bodies have become the repository for large quantities of every type of substance extraneous to the natural aquatic environment. The knowledge of hydrodynamics becomes crucial in this context, as it is the driving mechanism for the movement and transport of these matters and of sediments that become collectors of these substances, in a surface water system. The best way to understand these natural processes is via examples and case studies. This book deals with practical studies of hydrodynamic processes through physical and numerical models. Researchers, together with practicing engineers, will find this book useful in making a rapid assessment of different environmental water body problems

Statistical Analysis of Bathing Water Quality in Puglia Region (Italy)

Geostatistic analysis was applied to the dataset from multi-year monitoring, in the Apulian marine-coastal zone (Mediterranean Sea, Italy), on the presence and abundance of intestinal Enterococci and Escherichia coli, microbiological indicators of faecal contamination at the sea. The same faecal contamination can be considered as the main cause of pollution phenomenon under current Italian and European regulations for the bathing waters (Italian Government Decree 116/2008, European Directive 2006/7/CE). The main objective of the study is to verify, taking into the account the anthropic pressures acting on the coastal zone, the efficiency of the Apulian regional monitoring plan currently in force for the assessment of bathing waters quality, with a view to a hypothetical reduction of sample collection points