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The processes of transport and mixing in stratified open channel flows are investigated in this thesis. Detailed measurements of velocity and salinity were conducted, through the use of Laser-Induced Fluorescence (LIP) technique together with Laser Doppler anemometry, so that the effects of secondary current and stratification on the flow behaviour could be analysed. Two configurations were investigated: a rectangular open channel, and a compound open channel. For each configuration, four different stratification levels were analysed. The main flow characteristics, such as corner flow and velocity dip in a rectangular channel, and the twin vortices formed in compound channels, were found to be affected by stratification. In order to understand the mechanisms involved in secondary flow generation, the vorticity balance was carried out. Through the vorticity balance, the contribution of each term in the longitudinal vorticity equation could be evaluated. The mechanisms involved in the turbulence generation were also verified through the turbulent kinetic energy (TKE) budget. One of the contributions of this work refers to the understanding of the effects of stratification on turbulence and secondary flow generation. The exchange coefficients of momentum and solute were also investigated. These coefficients were found to depend not only on stratification level but also on other flow parameters, like for instance the aspect ratio. A new formulation is proposed for narrow channels, but more research is necessary in order to evaluate the effect of other parameters on the exchange coefficients.

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Many efforts have been conducted for improving the operation and management of open channel networks. Implementing simulation models and software is an effective step in achieving better operation of control structures in open channel networks. The purpose of this study was to develop a tool in ArcGIS for assisting the open channel network managers in operating flow control structures. This model presents a time schedule for gate operation based on the demands at turnouts through the water usage schedule of the network. The developed model was designed to be added as a tool to ArcToolbox in ArcGIS. Any ArcGIS user who has access to ArcView or ArcInfo can add this tool to ArcToolbox. Using ArcGIS Geoprocessing tools, ModelBuilder, Scripting and ArcToolbox tools, the proposed model, "Arc-Canal", was created. Arc-Canal is implementable for irrigation networks that open channel network are digitized in ArcGIS. Simulation is for the gravity flow in open channels without any pump in the network. Calculations are based on steady flow. All hydraulic calculations for water level, gates, and weirs are based on the methods defined in "Open-Channel Hydraulics" (Chow 1959). Most of the available flow simulation models are complicated individual software for which user needs to be trained to install and use it. Also most of these software are not free accessible. Arc-Canal is an easy to use tool that anyone with the knowledge of working with ArcGIS can run it. By adding the tool to ArcToolbox and following the described naming method, and entering the required data, model is ready to run. The developed model is a free access tool. Most of the channels in open channel networks in south Texas have mild bottom slope and flow is steady gravity flow. It is desired that the developed model will be a tool to assist irrigation districts in south Texas.

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Yes / The present study investigates the turbulent hydrodynamics in an open channel flow with an emergent and sparse vegetation patch placed in the middle of the channel. The dimensions of the rigid vegetation patch are 81 cm long and 24 cm wide and it is prepared by a 7× 10 array of uniform acrylic cylinders by maintaining 9 cm and 4 cm spacing between centers of two consecutive cylinders along streamwise and lateral directions respectively. From the leading edge of the patch, the observed nature of time averaged flow velocities along streamwise, lateral and vertical directions is not consistent up to half length of the patch; however the velocity profiles develop a uniform behavior after that length. In the interior of the patch, the magnitude of vertical normal stress is small in comparison to the magnitudes of streamwise and lateral normal stresses. The magnitude of Reynolds shear stress profiles decreases with increasing downstream length from the leading edge of the vegetation patch and the trend continues even in the wake region downstream of the trailing edge. The increased magnitude of turbulent kinetic energy profiles is noticed from leading edge up to a certain length inside the patch; however its value decreases with further increasing downstream distance. A new mathematical model is proposed to predict time averaged streamwise velocity inside the sparse vegetation patch and the proposed model shows good agreement with the experimental data. / Debasish Pal received financial assistance from SRIC Project of IIT Kharagpur (Project code: FVP)

A research report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in partial fulfillment of the requirements for the degree of Master of Science in Engineering Johannesburg, 2017 / The development of methods which are better able to predict the effect of large scale emergent roughness elements on the flow characteristics requires a better understanding of the drag coefficient under conditions likely to occur in the field. A laboratory investigation was carried out with newly developed equipment to quantify the drag force on various shaped cylinders, as well as the drag on an individual cylinder surrounded by an array of cylinders. The relationship between the drag coefficient and cylinder Reynolds number for a single circular cylinder was found to be of similar form but larger in magnitude than the established relationship for an infinitely long cylinder; the relationship departs from the infinite cylinder relationship for low cylinder Reynolds numbers. Contrary to previous research, the results for the multiple cylinder investigation did not reveal a clear relationship between the cylinder density and drag coefficient. Equations were developed and verified with existing laboratory data. These should be improved and extended by further research for field use. / MT2017

Flow-vegetation interactions are critically important for most hydraulic and sediment processes in streams and rivers and thus need to be accounted for in their management. The central goal of this project therefore was to improve the understanding of flow-vegetation interactions in patchy-vegetated river beds, which are typical in rivers. Based on laboratory experiments covering a range of selected hydraulic and patch mosaic scenarios, the hydraulic resistance mechanisms, turbulence structure, and transport mechanisms were studied. The effects of regular patch mosaic patterns (aligned and staggered) on the bulk hydraulic resistance were investigated first. For the cases in which the relative vegetation coverage BSA in respect to the total flume bed is low (BSA = 0.1), the patches mutual positions do not affect values of the friction factor. When the parameter BSA increases to intermediate values (BSA = 0.3), the spatial distribution of the vegetation patches and their interactions become crucial and lead to a significant increase in the bulk hydraulic resistance. When further increase of the vegetation cover occurs (BSA = 0.6), the effects on hydraulic resistance of patch patterns vanish. To clarify the mechanisms of the revealed patch effects on the overall hydraulic resistance, flow structure was assessed at both scales: individual patch and patch mosaic. The presence of a submerged isolated vegetation patch on the bed introduces a flow diversion which strongly alters the velocity field and turbulence parameters around the patch. Coherent structures, generated at the canopy top due to velocity shear, control the mass and momentum transfer between the layers below and above the vegetation patch. At the patch mosaic scale, a complex three-dimensional flow structure is formed around the patches which depends on the patch spacing and spatial arrangements. For the low surface area blockage factor (BSA = 0.1), the patches are sparsely distributed and the wakes are (nearly) fully developed before they are interrupted by the effects of the downstream patches. At the intermediate surface area blockage factor (BSA = 0.3), significant differences in flow structure between the aligned and staggered patches were observed. For the highest surface area blockage factor investigated (BSA = 0.6) both aligned and staggered patch mosaic configurations showed a similar behaviour. The results on the flow structure are used to provide mechanistic explanation of the observed patch mosaic effects on the bulk hydraulic resistance.

A promising feedstock for biofuels is microalgae. The most economical means of cultivating microalgae is via open raceway ponds. However, a large gap in economic feasibility exists between algae-based biofuels and traditional petroleum fuels. Recent research at Utah State University has focused on increasing biomass growth by implementing Delta Wings (DWs). DWs are placed facing the incoming flow, with a 40 degree angle of attack to create large vortices which travel downstream. The trailing vortices increase vertical mixing, which in turn increases algal growth. Past researchers at USU quantified vertical mixing with new metrics, optimized various raceway operating conditions, and established a positive correlation between the newly defined metrics and algal growth. Research was performed with the aid of a small-scale clear acrylic raceway. Both stereo particle image velocimetry (SPIV) and acoustic Doppler velocimetry (ADV) were used to estimate the recently defined mixing metric: the vertical mixing index (VMI). The focus of this work is to ascertain additional preferred operating conditions, in particular those unique to large scale raceways, with the aid of a computational fluid dynamics (CFD) model validated by experimental data. Three case studies are presented herein, which analyze the DW vertical position (VP), array spacing ratio (ASR), and the projected height to depth ratio (PHDR). The criteria for these studies are the VMI and power consumption. While it was previously assumed that vertically centering the DW centroid was optimal, the first case study revealed the ideal VP to be far lower. The lowest possible VP allows the trailing vortices to travel further downstream, resulting in increased vertical mixing. The second case study entails modeling complete arrays of DWs with various spacing. This model was the first to account for an increase in the number of allowable DWs with a decrease in array spacing. The ASR study revealed the ideal array spacing to be approximately half a DW, as opposed to the initial estimate of a full DW. The third case study confirmed the largest allowable DW to be superior.