This thesis focuses on generating real world turbulence levels in a water tunnel rotor test using fractal grids and characterizing the effect of the fractal grid generated-turbulence on the performance of hydrokinetic turbines. The research of this thesis is divided into three studies: one field study and two laboratory studies. The field study was conducted at the Canadian Hydro Kinetic Turbine Test Centre (CHTTC) on the Winnipeg River. An Acoustic Doppler Velocimeter (ADV) was used in the field study to collect flow measurements in the river. The laboratory studies were conducted at the University of Victoria (UVic) fluids research lab and the Sustainable Systems Design Lab (SSDL). In addition, the Particle Image Velocimetry (PIV) technique was used in the experiential studies to obtain quantitative information about the vector flow field along the test section, both upstream and downstream of the rotor’s plane. The first study is a field study aiming to provide real flow characteristics and turbulence properties at different depths from the free-surface to boundary layer region of a fast river current by conducting a field study in the Winnipeg River using ADV. A novel technique to deploy and control an ADV from free-surface to boundary layer in a fast-current channel is introduced in this work. Flow characteristics in the river, including mean flow velocities and turbulence intensity profiles are analyzed. The obtained results indicate that the maximum mean velocity occurs below the free-surface, suggesting that the mean velocity is independent of the channel depth. From the free-surface to half depth, it was found that changes in both the mean velocity and turbulence intensity are gradual. From mid-depth to the river bed, the mean velocity drops rapidly while the turbulence intensity increases at a fast rate. The turbulent intensity varied from 9% at the free-surface to around 17.5% near the river bed. The results of this study were used in the second lab study to help designing a fractal grid for a recirculating water flume tank. The goal was to modify the turbulence intensity in the water tunnel such that the generated turbulence was similar to that in the river at a location typical of a hydrokinetic device. The properties of fractal-generated turbulence were experimentally investigated by means of 2D Particle Image Velocimetry (PIV). The streamwise turbulent intensity profiles for different grids along the channel are presented. Additionally, visualization of the average and fluctuating flow fields are also presented. The results are in good agreement with results in literature. The third and final study investigated the power coefficient of a scale hydrokinetic turbine rotor in controlled turbulent flow (7.4 % TI), as well as in the low-turbulence smooth flow (0.5% TI) typical of lab scale testing. PIV was employed for capturing the velocity field. The results show that using realistic TI levels in the water tunnel significantly decrease the turbine’s power coefficient compared to smooth flow, highlighting the importance of considering this effect in future experimental campaigns. / Graduate

Published Article / This study investigates the use of off-grid micro-hydrokinetic river system as a cost-effective and sustainable electricity supply option for remote rural residents in close proximity to flowing water and not having access to grid electricity. This hydrokinetic technology is still in the development stage and there is a lack of application especially in rural areas with reasonable water resource. This study will present the economic and environmental benefits of the proposed system. A mathematical model is developed to simulate the system performance as submitted to different solicitations. A test prototype will also be used in order to validate the simulation results.

Numerical simulation allows investigation into the influence of separation distance and rotation on the performance of two vertical-axis hydrokinetic turbines. Compu- tational fluid dynamics is applied to calulate the lift and drag coefficients acting upon interacting NACA 0021 turbine blades for a Reynolds number of Red = 10, 000. To understand the effect of separation distance, large-eddy simulation of the flow around side-by-side and staggered cylinders, ReD = 3,000, and airfoils, Rec = 3,000, are also performed. Based upon the simulations, a drag reduction of 11.3% and 19.8% is determined for the downstream cylinder and airfoil, respectively. A reduction in Reynolds stresses is also observed for the staggered configuration compared to the side-by-side configuration. Due to computational resources of large-eddy simulation, the Reynolds averaged Navier-Stokes method is also applied to investigate the influence of separation distance and rotation on two vertical axis hydrokinetic turbines. The numerical simulations show that a drag reduction of 15.5% occurs when the non-dimensional spanwise and streamwise separation distances, based on turbine diameter, reach 1 and 2, respectively. / October 2016

Hydrokinetic tidal power is a novel and emergent technology undergoing continuous advancement with much of the progress focused on large utility scale projects. This resource is potentially underutilized because much of the coastal United States, despite having substantial tidal currents, do not have the deep and wide environments required by most of the developing turbine technology. This dissertation includes a detailed characterization of the tidal hydrodynamics for Rose Dhu Island, Georgia used for a tidal energy resource assessment as well as a general feasibility study for tidal estuaries with extensive wetlands. For predictions and evaluation of the estuarine hydrodynamics, data from an existing numerical model of the estuary encompassing the island is utilized. Field measurements in close proximity to the island are used to calibrate the model as well as characterize local hydrodynamic features. After the model calibration, the simulation data is used to evaluate the hydrodynamics. Wetland dominated estuaries commonly have a high degree of non-linear distortion which govern the relative durations and strengths of the tidal stages and thus the overall hydrodynamics and incoming hydrokinetic energy. The Ogeechee Estuary is characterized as ebb dominant with peak ebb and flood volume fluxes near high tide as a result of the increased storage capacity of the wetlands. Lowering the average wetland elevation in the model decreased ebb dominance and quickened the transition from flood to ebb tide. Increased domain friction in the model removed energy from the system and reduced ebb dominance. Enhanced model marsh friction reduced lateral flooding of the wetlands as well as ebb dominance. Localized measurements surrounding the island are analyzed to determine a location near the southwest coast of the island as a hydrokinetic energy hotspot. A kinematic and dynamic analysis is performed using channel transect measurements to identify key physical processes behind the hotspot formation. The hotspot forms due to sub-critical flow acceleration over a singular bump in the topography. High streamwise momentum is further concentrated at the hotspot due to secondary circulation cells across the channel. Flood tide circulation is characterized by two co-rotating cells induced by channel curvature and delineated by the bump. Ebb circulation consists of two counter-rotating cells from flow confluence of two upstream channels. Once the hydrodynamics are understood, the theoretical and technical resource assessment of the island is completed. A sensitivity analysis of hydrokinetic energy and tidal distortion is performed on synthetic data. For a principle constituent and its first harmonic, distortion greatly changes as does the distribution of velocities and energy as the relative phase varies. While the theoretical energy remains consistent, the technical energy can greatly vary. This effect is reduced with the addition semi-lunar variation. Using a simplified analytical method, the maximum average channel power is estimated as 8.80 MW. For the hotspot it is estimated that there is 30.3 MWh available to capture yearly with an average power of 3.46 kW for a turbine with an area of 10 square meters. For the same turbine area with conservative efficiencies, the hotspot could provide a yearly technical energy of 10.9 MWh with an average power of 1.25kW for the island. Due to the complex localized hydrodynamics, both the theoretical and technical resource varies greatly across and along the channel. These considerations are more pertinent when performing a hydrokinetic energy resource assessment in a marsh estuary than for large scale bay-ocean exchange environments, the present industry focus.

Magistrantūros studijų baigiamasis darbas 52 lapai, 30 paveikslų, 4 lentelės, 41 literatūros šaltiniai. PAGRINDINIAI ŽODŽIAI: Hidrokinetinė energija, turbinos, nepatvankinė technologija, hidroelektrinė. Tiriamojo darbo objektas: Nepatvankinių technologijų panaudojimas upių hidrokinetinės energijos gavybai. Tiriamojo darbo tikslas: Įvertinti nepatvankinių energijos gavybos technologijų ir aplinkosaugos priemonių integracinius suderinamumus. Tiriamojo darbo uždaviniai: 1. Apžvelgti hidrokinetinės energijos panaudojimo taikant nepatvankines technologijas patirtį užsienio šalyse. 2. Apžvelgti hidrokinetinės energijos taikant nepatvankines technologijas panaudojimo siekius Lietuvoje. 3. Išanalizuoti nepatvankinių technologijų schemas. 4. Išanalizuoti nepatvankinių technologijų poveikį vandens ekosistemoms. 5. Įvertinti galimas nepatvankinių technologijų poveikio vandens ekosistemoms sumažinimo priemones. Tiriamojo darbo metodika: literatūros apžvalgos skyrius rašomas referatyviai, analizuojant mokslinius šaltinius. Duomenys tyrimui renkami analizuojant lietuvišką ir užsienio literatūrą, patentus, schemas, didžiausią dėmesį atkreipiant į nepatvankines energijos gavybos technologijas ir jų poveikį aplinkai. Tiriamojo darbo rezultatai: 1. Literatūros analizėje apžvelgta hidrokinetinės energijos panaudojimo taikant nepatvankines technologijas patirtis Lietuvoje, bei užsienyje. 2. Išanalizuotos nepatvankinių technologijų schemos, bei nepatvankinių technologijų poveikis... [toliau žr. visą tekstą] / The final master work consisting of 52 sheets, 30 images, 4 tables, 41 sources of literature. Key words: hydrokinetic energy, turbines, non-affluent technology, hydroelectric power plant. The object of this work: use of non – affluent technologies in extracting hydrokinetic energy out of the rivers. Main goal of this work: estimate the compatibility between non – affluent energy extracting technologies and tools of environment control integrity. Tasks of this work: 1. Overview of the hydrokinetic energy use abroad applying non – affluent technologies. 2. Overview of the hydrokinetic energy implementation and goals into Lithuanian market. 3. Analyses of the schemes about non – affluent technologies. 4. Analyze the impact of non-affluent technologies to eco systems. 5. Estimate the possible tools for decreasing impact of the non-affluent technologies to water eco systems. Methodology of this work: Literature overview charter is written abstractly analyzing scholarly sources. Data for the research was collected by analyzing Lithuanian and foreign literature, licenses, schemes considering non-affluent energy extraction technologies and their impact to the environment. The results of the work: 1. In literature analysis overviewed the experience of the hydrokinetic energy use applying non-affluent technologies in Lithuania and abroad. 2. Analyzed the schemes of the non – affluent technologies and their impact to the eco systems. 3. Estimating the tools for decreasing impact of the... [to full text]

This thesis proposes equations extending the Free Surface Actuator Disc Theory to yield drag forces and interference factors from a series of two porous discs in open channel flows. The new model includes blockage ratio and Froude number as independent variables, which are inferred in advance to yield a single solution in the prescribed domain. The theoretical extension is integrated with the Blade Element Theory in a Double Multiple Streamtube model (DMS) to predict axial loads and the performance of confined Darrieus turbines. The turbine thrust force influences the flow approaching the rotor. Hence, a momentum method is applied to solve the hydraulic transition in the channel, achieving the unknown inflow factor from the undisturbed flow imposed downstream. The upstream blockage ratio and Froude number are thus updated iteratively to adapt the DMS to subcritical applications. The DMS is corrected further to account for the energy losses due to mechanical struts and turbine shaft, flow curvature, turbine depth, and streamtube expansion. Sub-models from the literature are partly corrected to comply with the extended actuator disc model. The turbine model is validated with experimental data of a high-solidity cross-flow hydrokinetic turbine that was previously tested at increasing rotor speeds. Turbine arrays are investigated by integrating the previous turbine model with wake sub-models to predict the plant layout maximizing the array power. An assessment of multi-row plants shows that the array power improves with closely spaced turbines. In addition, highly spaced arrays allow a partial recovery of the available power to be exploited upstream by a new turbine array. The highest array power is predicted by simulations on different array layouts considering constant array blockage ratio and rotor solidity. Finally, assuming a long ideal channel, the deviation in the inflow depth is speculated to become asymptotic after many arrays, implying almost identical power conversion upstream.

No description available.

The predictive capabilities of blade-resolved unsteady Reynolds averaged Navier-Stokes (URANS) and detached eddy simulation (DES), the most commonly used hybrid RANS/large eddy simulation (LES) model, are assessed for hydrokinetic turbine performance and mean and turbulent flows in the intermediate-wake region, and results for a range of tip-speed ratio encompassing design and off-design conditions are analyzed to understand the wake recovery mechanism. The performance predictions compared within 5% of the experimental data. Both URANS and DES models performed reasonably well for the near wake predictions, where the errors were < 15%. DES outperformed URANS for both mean wake deficit and turbulence predictions in the intermediate-wake region and both quantities compared within 10% of the experiments. The improved prediction by DES is because of 1) its ability to predict the tip vortex breakdown, which plays a critical role in the wake recovery, especially for higher tip speed ratios; 2) the presence of the free-surface which created an upper bypass region of accelerated flow. The study reveals that the tip vortex breakdown mechanism depends on tip speed ratio. For lower values of tip speed ratio, instabilities generated in the root vortex core are identified to be the cause of breakdown. For higher values, the breakdown occurred because of the instabilities generated during the vortex filament entanglement. The presence of the free-surface led to an early vortex breakdown and the interaction between the wake and free-surface is initiated by the interaction of stanchion with the free-surface. Future work should focus on investigation of other hybrid RANS/LES models to address the limitations of the DES models, and extension of the study to include wave effects.

The flow velocity in a river is three-dimensional (3D), turbulent, and varies in time and space. Capturing this variability in field measurements to support studies of river processes has proven particularly challenging. While originally developed to measure discharge, boat-mounted acoustic Doppler current profilers (ADCP) are increasingly used in field studies to quantify flow features including mean velocity, boundary shear stress, and sediment motion. Two survey procedures are typically employed with an ADCP. Moving-vessel (MV) measurements provide spatially-rich velocity data while temporally-rich data are obtained with fixed-vessel (FV) procedures. Given the relative ease of MV measurements, recent work has focused on developing MV procedures that produce comparable results to FV measurements. At the present, results of this work are inconclusive. Additionally, there is a lack of reported data and procedures for FV measurements. This work seeks to develop techniques to present 3D velocity data obtained in natural rivers in a unified framework. This framework is based on a stream-fitted coordinate system defined by the flow direction at a cross section and allows for 3D velocity to be decomposed into streamwise, spanwise, and vertical components. Procedures are developed to assure that the velocity profiles measured at fixed locations are (1) not negatively impacted by the inevitable motion of the ADCP, (2) statistically stationary, and (3) of sufficient record length to determine the mean velocity. The coordinate system allows time-averaged velocity from FV procedures to be compared with spatially-averaged velocity from MV vessels. Significant differences are found between the two survey procedures, particularly for secondary velocity components. Ultimately, integrating results of the two survey procedures leads to an improved representation of the mean flow field. The techniques are applied to data obtained on a study reach on the lower Roanoke River, located in eastern North Carolina. / Ph. D.

Dans le cadre de la production d'électricité par énergie renouvelable, cette thèse a pour objectif de contribuer à l'amélioration des performances hydrodynamiques des hydroliennes à flux transverse conçues par HydroQuest. Pour y parvenir, deux axes d'étude principaux sont proposés. Le premier consiste à améliorer la compréhension de la performance de l'hydrolienne et de l'écoulement en son sein par voie numérique. L'influence du paramètre d'avance ainsi que celle de la solidité de l'hydrolienne sont étudiées. Les écoulements mis en jeux étant complexes, une méthode de type Simulation des Granges Échelles 3D est utilisée afin de les restituer au mieux. Le phénomène de décrochage dynamique, qui apparaît pour certains régimes de fonctionnement de l'hydrolienne, fait l'objet d'une étude à part entière sur un cas de profil oscillant.Le second axe se concentre sur les carénages de l’hydrolienne qui font l'objet d'une procédure d'optimisation numérique. Afin de pouvoir réaliser les nombreuses simulations requises en un temps réaliste, des méthodes de type Unsteady Reynolds-Averaged Navier-Stokes 2D moins coûteuses et fournissant une précision suffisante pour ce type d'étude sont utilisées. / Within the renewable electricity production framework, this study aims to contribute to the efficiency improvement of the Vertical Axis Hydrokinetic Turbines designed by HydroQuest. To achieve this objective, two approaches are used. The first consists in the improvement of the comprehension of the turbine efficiency such as the flow through the turbine by numerical means. The influence of the tip speed ratio such as the turbine soldity are investigated. The flow through the turbine is complex. A 3D Large Eddy Simulation type is thus used. The dynamic stall phenomenon which could occur in Vertical Axis Hydrokinetic Turbines is also studied in a oscillating blade configuration.The second approach consists in the numerical optimization of the turbine channeling device. To perform the high number of simulations required, a 2D Unsteady Reynolds-Averaged Navier-Stokes simulation type is used.