Part I presents the statistical theory of turbulence, and Part 2 the coherent structures in open-channel flows and boundary layers. The book is intended for advanced students and researchers in hydraulic research, fluid mechanics, environmental sciences and related disciplines. References Index.

Turbulence in open-channel flows

The paper promotes an emerging research area at the interfaces between aquatic ecology, biomechanics and environmental fluid mechanics. This new area, Hydrodynamics of Aquatic Ecosystems, bridges these disciplines together and is defined as a study of flow-organism interactions at multiple scales with particular focus on relevant transport processes and mutual physical impacts. Being an important part of its mother disciplines, Hydrodynamics of Aquatic Ecosystems deals with two key interconnected issues: (i) physical interactions between flow and organisms (e.g. due to an interplay between flow-induced forces and reaction forces generated by organisms) and (ii) ecologically relevant mass-transfer-uptake processes (e.g. due to molecular and turbulent diffusion). Key concepts and tools of Hydrodynamics of Aquatic Ecosystems are outlined first and then a promising approach that may provide a unifying platform for coupling and integrating ecological, hydrodynamic and biomechanical processes, known as the double-averaging methodology (DAM), is discussed. Copyright © 2009 John Wiley & Sons, Ltd.

Hydrodynamics of aquatic ecosystems: An interface between ecology, biomechanics and environmental fluid mechanics

Turburence structure and coherent motion in vegetated canopy open-channel flows

From the blade scale to the reach scale: A characterization of aquatic vegetative drag

The presence of vegetation modifies flow and sediment transport in alluvial channels and hence the morphological evolution of river systems. Plants increase the local roughness, modify flow patterns and provide additional drag, decreasing the bed-shear stress and enhancing local sediment deposition. For this, it is important to take into account the presence of vegetation in morphodynamic modelling. Models describing the effects of vegetation on water flow and sediment transport already exist, but comparative analyses and validations on extensive datasets are still lacking. In order to provide practical information for modelling purposes, we analysed the performance of a large number of models on flow resistance, vegetation drag, vertical velocity profiles and bed-shear stresses in vegetated channels. Their assessments and applicability ranges are derived by comparing their predictions with measured values from a large dataset for different types of submerged and emergent vegetation gathered from the literature. The work includes assessing the performance of the sediment transport capacity formulae of Engelund and Hansen and van Rijn in the case of vegetated beds, as well as the value of the drag coefficient to be used for different types of vegetation and hydraulic conditions. The results provide a unique comparative overview of existing models for the assessment of the effects of vegetation on morphodynamics, highlighting their performances and applicability ranges. Copyright © 2014 John Wiley & Sons, Ltd.

Effects of vegetation on flow and sediment transport: comparative analyses and validation of predicting models

/pdf/piv-and-ptv-measurements-in-hydro-sciences-with-focus-on-1tj34xwim8.pdf

PIV and PTV measurements in hydro-sciences with focus on turbulent open-channel flows

Meandering compound open-channel flow is of high interest in river engineering and flood disaster In particular, cross-sectional secondary currents develop significantly associated with an interaction between meandering inbank main-channel flow and straight overbank floodplain flow These currents promote mass and momentum exchanges between them, as well as sediment transport and bed erosion Further, organized motions may be generated in the same manner as typical horizontal vortices in straight compound channels However, there is limited detailed information on the generation process of organized motion and secondary currents This study focuses on the 3D structure of horizontal coherent motion and its advection property in the channel-transition zone from the straight to meandering compound open-channel flows by using a multi-layer scanning PIV, and compares them with those of continuous meandering channel flowsA strong relation between the horizontal vortices and secondary currents was obtained, re

Turbulence structure and coherent motion in meandering compound open-channel flows

Consecutive groynes and embayments form dead water zones, where sedimentation and high concentrations of pollutants are often observed. It is thus very important to understand the mass and momentum exchange between the main channel and side cavities in rivers and hydraulic engineering structures. The spanwise gradient of the streamwise velocity near the junction produces small-scale turbulent vortices because of shear instability. Furthermore, large-scale horizontal circulation is also generated in the cavity zone. These coherent turbulent structures play a significant role in mass and sediment transfer at the boundary between the mainstream and embayment. However, the relation between turbulence and mass transfer is poorly understood. In this study, we performed particle image velocity and laser-induced fluorescence experiments using a laboratory flume, laser light sheets and a high-speed CMOS camera. We examined the exchange properties of a dye as a function of bed configuration and sedimentation effect. Both primary and secondary gyres were observed in the flat bed and downward-sloping bed, whereas the primary gyre was prevalent in the upward-sloping bed. Moreover, the horizontal circulation strongly affected the mass-transfer properties between the mainstream and side cavity.

/pdf/hydrodynamic-characteristics-and-related-mass-transfer-dx5e19g4xk.pdf

Hydrodynamic characteristics and related mass-transfer properties in open-channel flows with rectangular embayment zone

Vegetation such as trees and shrubs are often observed at the floodplain edge in natural rivers. Spanwise profiles of streamwise velocity component are influenced significantly by the drag force of trees. That is to say, the streamwise velocity decreases locally behind trees and near the junction between the main-channel and the floodplain. This property is quite different from that observed in typical compound open-channel flows, in which the velocity profile has a single inflection point and forms a mixing layer related to large-scale horizontal vortices. In contrast, in compound open-channel flow with a one-line emergent vegetation, a “V”-shaped velocity profile appears with twin inflection points. It is thus very important to investigate these hydrodynamic properties and turbulence structure considering the emergent vegetation effects in river engineering and eco hydraulics. So, in the present study, turbulence measurements by 3-D acoustic Doppler anemometer (ADV) were conducted in 150cm wide laboratory flume, in which 2cm diameter and 25cm height cylinders are placed as vegetation models with 10cm span along the junction edge.

Michio Sanjou

Papers

Turburence structure and coherent motion in vegetated canopy open-channel flows

PIV and PTV measurements in hydro-sciences with focus on turbulent open-channel flows

Turbulence structure and coherent motion in meandering compound open-channel flows

Hydrodynamic characteristics and related mass-transfer properties in open-channel flows with rectangular embayment zone

Turbulence structure of compound open-channel flows with one-line emergent vegetation