國立虎尾科技大學 |

Design and Scaling of Cross-Flow Turbines in Variable Confinement.

紀錄類型:	書目-語言資料,手稿 : Monograph/item
正題名/作者:	Design and Scaling of Cross-Flow Turbines in Variable Confinement./
作者:	Hunt, Aidan.
面頁冊數:	1 online resource (202 pages)
附註:	Source: Dissertations Abstracts International, Volume: 86-01, Section: B.
Contained By:	Dissertations Abstracts International86-01B.
標題:	Alternative energy. -
電子資源:	click for full text (PQDT)
ISBN:	9798383221303

Design and Scaling of Cross-Flow Turbines in Variable Confinement.
Hunt, Aidan.

Design and Scaling of Cross-Flow Turbines in Variable Confinement. - 1 online resource (202 pages)

Source: Dissertations Abstracts International, Volume: 86-01, Section: B.

Thesis (Ph.D.)--University of Washington, 2024.

Includes bibliographical references

Cross-flow turbines can convert the energy in wind or moving water into renewable power. The efficiency and loading characteristics of a cross-flow turbine depend on both the geometric configuration of the rotor and the properties of the flow the turbine operates in, with the combined effects of these factors influencing the engineering design, control, and management of these systems. However, due to their unsteady fluid dynamics, it can be difficult to predict how the interactions between turbine geometry and flow characteristics affect performance and shape optimal turbine design. Consequently, the aim of this research is to experimentally examine how the interplay between cross-flow turbine geometry and flow characteristics influences the dynamics that govern turbine performance, with the overall goals of identifying pathways for improving their power conversion efficiency and to provide experimental data for the validation of simulations and reduced-order models. This work focuses on two key flow parameters: the Reynolds number (which represents the turbine scale relative to the scale of the flow) and the blockage ratio (which represents how much of a channel is occupied by a turbine in confined flow). Additionally, this work considers three aspects of the rotor geometry: the number of blades, the chord-to-radius ratio, and the preset pitch angle. The first objective of this work is to evaluate the interplay between the Reynolds number, the chord-to-radius ratio, the preset pitch angle, and the blade count on cross-flow turbine performance through parametric variation of these variables in a large-scale experiment. The results provide a better understanding of the effects of each parameter, as well as how their combined effects influence turbine hydrodynamics across a range of device scales. The second objective of this work is to examine the effects of confinement on the performance and near-wake characteristics of a two-rotor cross-flow turbine array, with an emphasis on the upper end of practically-achievable blockage ratios in river or tidal channels. These blockage ratios are relevant to full-scale turbine deployments, but have received limited experimental investigation. The results improve our understanding of how turbine performance evolves across a wide range of blockage ratios, and allow us to evaluate how well commonly-used analytical models based on linear momentum theory can represent real turbines at high confinement. Third, we combine the methodologies employed to address the first two objectives to examine how the effects of the chord-to-radius ratio, preset pitch angle, and blade count are influenced by confinement. This provides the first experimental examination of the interplay between confinement and rotor geometry on turbine performance, and illuminates key design principles for turbines in confined flows.Although the effects of the Reynolds number, chord-to-radius ratio, preset pitch angle, and blade count have been investigated in prior work, the combined influences of these parameters on cross-flow turbine performance have not been systematically explored. To examine how turbine scale influences the optimal rotor geometry, we conduct 223 unique experiments across an order of magnitude of diameter-based Reynolds numbers (~80,000 - 800,000), in which the performance implications of the chord-to-radius ratio, preset pitch angle, and number of blades are evaluated. In agreement with prior work, maximum performance is generally observed to increase with Reynolds number and decrease with blade count. The broader experimental space clarifies parametric interdependencies; for example, the optimal preset pitch angle is increasingly negative as the chord-to-radius ratio increases. As these experiments vary both the chord-to-radius ratio and blade count, the performance of different rotor geometries with the same solidity (the ratio of total blade chord to rotor circumference) can also be evaluated. The results demonstrate that while solidity can be a poor predictor of maximum performance, across all scales and tested geometries it is an excellent predictor of the tip-speed ratio corresponding to maximum performance. Overall, these results present a uniquely holistic view of relevant geometric considerations for cross-flow turbine rotor design and provide a rich dataset for validation of numerical simulations and reduced-order models. Although this work focuses primarily on cross-flow turbines in water channels, the key results are also applicable to wind-driven cross-flow turbines under similar conditions.The performance and near-wake characteristics of a turbine in a confined flow depend on the blockage ratio, but limited experimental investigation has been performed for turbine performance at the upper range of practically-achievable blockage ratios, which have been hypothesized as a mechanism for reducing cost of energy. Furthermore, while linear momentum actuator disk theory is frequently used to model turbines in confined flows, how well these idealized models can represent the performance and flow fields around real turbines as confinement---and the attendant benefits---increase is largely untested. To address these gaps in understanding, we evaluate the performance and near-wake flow field of a two-rotor cross-flow turbine array at blockage ratios from 30% to 55%. In agreement with prior work, the array-averaged power and thrust coefficients generally increase with blockage, as does the tip-speed ratio at which the array produces the most power. We find that the measured fluid velocity in the bypass region is found to be well-predicted by linear momentum theory, while the measured wake velocity is not. From this, we show that linear momentum theory collapses the measured power and thrust coefficients across this range of blockage ratios when these coefficients are scaled by the bypass velocity in a manner inspired by the bluff-body theory of Maskell. Overall, this demonstrates that simple linear momentum models can be quantitatively descriptive of the dynamics of highly confined turbines. From this, an analytical method for predicting array performance as a function of blockage is developed. This work illuminates turbine performance at relatively high confinement and illustrates the unexpected suitability of analytical models for predicting and interpreting their hydrodynamics. Although the general effects of confinement on turbine performance are understood, how the optimal cross-flow turbine rotor geometry changes with the blockage ratio has not received significant attention in prior work. Therefore, we combine the methodologies of the preceding components of this research to parametrically examine how the interplay between the number of blades, the chord-to-radius ratio, the preset pitch angle, and the blockage ratio affect the performance of two-rotor cross-flow turbine array. The performance of 45 unique geometric configurations is evaluated at blockage ratios between 35% and 55%, resulting in 135 unique experiments. Array efficiency is found to increase with the blade count---an inversion of trends at lower blockage---whereas trends for the chord-to-radius ratio and preset pitch angle are similar to those at low blockage. When normalized by the corresponding bypass velocities predicted from linear momentum theory, the array-averaged power coefficients at maximum efficiency collapse for each geometry across the tested blockages, demonstrating the broader applicability of these analytical models across the geometric parameter space. While both the efficiency and thrust on the array generally increase with dynamic solidity at high blockage, the individual effects of the blade count and chord-to-radius ratio still influence performance. Overall, these results provide the first experimental investigation of how blockage shapes the optimal cross-flow turbine geometry, illuminating key design principles for turbines in confined flow.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2024

Mode of access: World Wide Web

ISBN: 9798383221303Subjects--Topical Terms:

1241221
Alternative energy.
Subjects--Index Terms:

BlockageIndex Terms--Genre/Form:

554714
Electronic books.

Design and Scaling of Cross-Flow Turbines in Variable Confinement.
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520 $a Cross-flow turbines can convert the energy in wind or moving water into renewable power. The efficiency and loading characteristics of a cross-flow turbine depend on both the geometric configuration of the rotor and the properties of the flow the turbine operates in, with the combined effects of these factors influencing the engineering design, control, and management of these systems. However, due to their unsteady fluid dynamics, it can be difficult to predict how the interactions between turbine geometry and flow characteristics affect performance and shape optimal turbine design. Consequently, the aim of this research is to experimentally examine how the interplay between cross-flow turbine geometry and flow characteristics influences the dynamics that govern turbine performance, with the overall goals of identifying pathways for improving their power conversion efficiency and to provide experimental data for the validation of simulations and reduced-order models. This work focuses on two key flow parameters: the Reynolds number (which represents the turbine scale relative to the scale of the flow) and the blockage ratio (which represents how much of a channel is occupied by a turbine in confined flow). Additionally, this work considers three aspects of the rotor geometry: the number of blades, the chord-to-radius ratio, and the preset pitch angle. The first objective of this work is to evaluate the interplay between the Reynolds number, the chord-to-radius ratio, the preset pitch angle, and the blade count on cross-flow turbine performance through parametric variation of these variables in a large-scale experiment. The results provide a better understanding of the effects of each parameter, as well as how their combined effects influence turbine hydrodynamics across a range of device scales. The second objective of this work is to examine the effects of confinement on the performance and near-wake characteristics of a two-rotor cross-flow turbine array, with an emphasis on the upper end of practically-achievable blockage ratios in river or tidal channels. These blockage ratios are relevant to full-scale turbine deployments, but have received limited experimental investigation. The results improve our understanding of how turbine performance evolves across a wide range of blockage ratios, and allow us to evaluate how well commonly-used analytical models based on linear momentum theory can represent real turbines at high confinement. Third, we combine the methodologies employed to address the first two objectives to examine how the effects of the chord-to-radius ratio, preset pitch angle, and blade count are influenced by confinement. This provides the first experimental examination of the interplay between confinement and rotor geometry on turbine performance, and illuminates key design principles for turbines in confined flows.Although the effects of the Reynolds number, chord-to-radius ratio, preset pitch angle, and blade count have been investigated in prior work, the combined influences of these parameters on cross-flow turbine performance have not been systematically explored. To examine how turbine scale influences the optimal rotor geometry, we conduct 223 unique experiments across an order of magnitude of diameter-based Reynolds numbers (~80,000 - 800,000), in which the performance implications of the chord-to-radius ratio, preset pitch angle, and number of blades are evaluated. In agreement with prior work, maximum performance is generally observed to increase with Reynolds number and decrease with blade count. The broader experimental space clarifies parametric interdependencies; for example, the optimal preset pitch angle is increasingly negative as the chord-to-radius ratio increases. As these experiments vary both the chord-to-radius ratio and blade count, the performance of different rotor geometries with the same solidity (the ratio of total blade chord to rotor circumference) can also be evaluated. The results demonstrate that while solidity can be a poor predictor of maximum performance, across all scales and tested geometries it is an excellent predictor of the tip-speed ratio corresponding to maximum performance. Overall, these results present a uniquely holistic view of relevant geometric considerations for cross-flow turbine rotor design and provide a rich dataset for validation of numerical simulations and reduced-order models. Although this work focuses primarily on cross-flow turbines in water channels, the key results are also applicable to wind-driven cross-flow turbines under similar conditions.The performance and near-wake characteristics of a turbine in a confined flow depend on the blockage ratio, but limited experimental investigation has been performed for turbine performance at the upper range of practically-achievable blockage ratios, which have been hypothesized as a mechanism for reducing cost of energy. Furthermore, while linear momentum actuator disk theory is frequently used to model turbines in confined flows, how well these idealized models can represent the performance and flow fields around real turbines as confinement---and the attendant benefits---increase is largely untested. To address these gaps in understanding, we evaluate the performance and near-wake flow field of a two-rotor cross-flow turbine array at blockage ratios from 30% to 55%. In agreement with prior work, the array-averaged power and thrust coefficients generally increase with blockage, as does the tip-speed ratio at which the array produces the most power. We find that the measured fluid velocity in the bypass region is found to be well-predicted by linear momentum theory, while the measured wake velocity is not. From this, we show that linear momentum theory collapses the measured power and thrust coefficients across this range of blockage ratios when these coefficients are scaled by the bypass velocity in a manner inspired by the bluff-body theory of Maskell. Overall, this demonstrates that simple linear momentum models can be quantitatively descriptive of the dynamics of highly confined turbines. From this, an analytical method for predicting array performance as a function of blockage is developed. This work illuminates turbine performance at relatively high confinement and illustrates the unexpected suitability of analytical models for predicting and interpreting their hydrodynamics. Although the general effects of confinement on turbine performance are understood, how the optimal cross-flow turbine rotor geometry changes with the blockage ratio has not received significant attention in prior work. Therefore, we combine the methodologies of the preceding components of this research to parametrically examine how the interplay between the number of blades, the chord-to-radius ratio, the preset pitch angle, and the blockage ratio affect the performance of two-rotor cross-flow turbine array. The performance of 45 unique geometric configurations is evaluated at blockage ratios between 35% and 55%, resulting in 135 unique experiments. Array efficiency is found to increase with the blade count---an inversion of trends at lower blockage---whereas trends for the chord-to-radius ratio and preset pitch angle are similar to those at low blockage. When normalized by the corresponding bypass velocities predicted from linear momentum theory, the array-averaged power coefficients at maximum efficiency collapse for each geometry across the tested blockages, demonstrating the broader applicability of these analytical models across the geometric parameter space. While both the efficiency and thrust on the array generally increase with dynamic solidity at high blockage, the individual effects of the blade count and chord-to-radius ratio still influence performance. Overall, these results provide the first experimental investigation of how blockage shapes the optimal cross-flow turbine geometry, illuminating key design principles for turbines in confined flow.
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