insight - Scientific Computing - # Hydrofoil Energy Harvesting

Experimental Study on Maximizing Energy Harvesting of Tandem Oscillating Hydrofoils by Optimizing Kinematic Interactions

Q: Could the performance gains observed from favorable wake-foil interactions be negated or even reversed in real-world conditions with factors like turbulence and unsteady flow?

Yes, the performance gains observed from favorable wake-foil interactions in controlled laboratory settings could be significantly impacted, potentially negated or even reversed, by the complexities of real-world conditions: Turbulence Disruption: Turbulence can disrupt the coherent vortex structures generated by the leading hydrofoil, which are essential for the favorable interactions that enhance trailing foil performance. This disruption can lead to less predictable and potentially less beneficial wake interactions. Unsteady Flow Velocities: Real-world flows are rarely uniform and steady. Fluctuations in flow velocity and direction can alter the trajectory and strength of wake vortices, making it challenging to maintain the precise phasing required for optimal energy extraction. Flow Direction Variations: Changes in flow direction, common in real-world tidal and riverine environments, can further disrupt the wake structure and lead to misalignment between the trailing foil and the incoming wake, reducing efficiency. Control System Robustness: Maintaining the optimal performance gains observed in the study under real-world conditions necessitates robust control systems. These systems must be capable of continuously sensing and adapting to dynamic flow conditions, adjusting individual foil kinematics to mitigate the negative impacts of turbulence and flow variability.

Q: What are the potential implications of these findings for understanding and mimicking the efficient locomotion of aquatic animals that utilize similar unsteady fluid dynamics principles?

The findings of this study hold significant implications for understanding and potentially mimicking the efficient locomotion of aquatic animals: Bio-Inspired Propulsion Systems: The study's demonstration of enhanced performance through precise control of wake interactions provides valuable insights for developing bio-inspired propulsion systems for underwater vehicles. By mimicking the synchronized and adaptable movements observed in fish schools, these systems could achieve significant efficiency improvements. Understanding Fish Schooling: The study's focus on wake interaction dynamics can contribute to a deeper understanding of the complex hydrodynamic interactions within fish schools. By analyzing how individual fish adjust their movements in response to the wakes generated by their neighbors, researchers can gain insights into the energy-saving mechanisms employed by these animals. Optimizing Underwater Vehicle Design: The findings related to optimal inter-foil spacing and phasing can inform the design of underwater vehicles operating in formation. By optimizing the arrangement and movement of multiple vehicles, engineers can potentially reduce energy consumption and enhance maneuverability. Developing Biomimetic Robots: The study's insights into unsteady fluid dynamics and wake control can contribute to the development of more agile and efficient biomimetic robots. These robots could be used for a variety of applications, including underwater exploration, environmental monitoring, and search and rescue operations.

Core Concepts

Tandem oscillating hydrofoils can achieve maximum energy harvesting efficiency when the trailing foil kinematics are tuned to leverage favorable wake-foil interactions, even if this requires deviating from the optimal kinematics of a single foil.

Abstract

Bibliographic Information: Handy-Cardenas, E.E., Zhu, Y., & Breuer, K.S. (2024). Optimal kinematics for energy harvesting using favorable wake-foil interactions in tandem oscillating hydrofoils. arXiv preprint arXiv:2411.00157v1.
Research Objective: This study investigates the optimal kinematic configurations for maximizing energy harvesting efficiency in a tandem oscillating hydrofoil system, focusing on the interaction between the wake of the leading foil and the trailing foil.
Methodology: The researchers conducted experiments in a water flume using two hydrofoils in a tandem arrangement. They systematically varied kinematic parameters such as heave and pitch amplitudes, inter-foil phase, and foil separation. Force and torque measurements were collected to determine power extraction, and Particle Image Velocimetry (PIV) was used to analyze wake structures and interactions.
Key Findings: The study identified three distinct wake regimes behind the leading foil: shear layer, leading-edge vortex (LEV), and LEV + trailing-edge vortex (LEV+TEV). The optimal system performance was achieved when the leading foil operated in the LEV regime, even though this did not correspond to the single-foil optimum. Trailing foil performance was maximized when its kinematics were tuned to either avoid or favorably interact with the wake vortices shed by the leading foil. The study also found that increasing the trailing foil's heave and pitch amplitudes, within certain limits, could enhance power extraction.
Main Conclusions: The authors conclude that optimizing the kinematics of tandem oscillating hydrofoils for favorable wake-foil interactions is crucial for maximizing energy harvesting efficiency. They demonstrate that the optimal configuration for the array differs from the single-foil optimum and highlight the importance of considering wake dynamics in the design of hydrofoil energy harvesting systems.
Significance: This research contributes to the understanding of wake-foil interactions in oscillating hydrofoil systems and provides valuable insights for optimizing the design and operation of hydrokinetic turbine arrays for energy harvesting.
Limitations and Future Research: The study was limited to a specific range of kinematic parameters and a fixed Reynolds number. Future research could explore a wider parameter space, different foil geometries, and the effects of varying Reynolds numbers. Investigating the performance of larger arrays with more than two foils would also be beneficial for practical applications.

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Stats

The optimal system power extraction was achieved in the LEV wake regime (αleT/4 ∼0.35).
The global optimum across all parameter combinations tested corresponded to the LEV regime with both foils operating with f ∗= 0.11.
The maximum trailing foil power extraction was observed at a wake phase parameter of Φ ∼100◦ in the LEV+TEV regime.
An optimal range of trailing foil αtrT/4 for all wake regimes was identified as 0.32 < αtrT/4 < 0.4.

Quotes

Key Insights Distilled From

Optimal Kinematics for Energy Harvesting Using Favorable Wake-Foil Interactions in Tandem Oscillating Hydrofoils

by Eric E. Hand... at arxiv.org 11-04-2024

https://arxiv.org/pdf/2411.00157.pdf

Optimal Kinematics for Energy Harvesting Using Favorable Wake-Foil Interactions in Tandem Oscillating Hydrofoils

Deeper Inquiries

How would the findings of this study translate to the design and optimization of larger hydrofoil arrays for practical energy harvesting applications?

This study provides valuable insights that can be leveraged for designing and optimizing larger hydrofoil arrays for practical energy harvesting:

Variable Kinematics for Enhanced Performance: The study demonstrates that allowing individual hydrofoils within an array to operate at different kinematics, as opposed to identical settings, can significantly improve overall energy harvesting efficiency. This finding suggests that future array designs should incorporate control systems capable of individually adjusting the heave amplitude (h0), pitch amplitude (θ0), and inter-foil phase (ψ1−2) of each hydrofoil.

Wake Regime Targeting:  The identification of the Leading Edge Vortex (LEV) regime as the optimal operating condition for maximum system power output is crucial.  Larger arrays can be designed to ensure that most hydrofoils operate within this regime, maximizing energy extraction from the wake interactions.

Inter-Foil Spacing Optimization: While the study found that inter-foil separation (Sx) did not significantly impact system power within the tested range, it highlighted the potential for closer spacing to increase power density. This is a critical consideration for practical applications where maximizing energy extraction within a limited area is essential. However, closer spacing necessitates precise control over individual foil kinematics to mitigate the detrimental effects of destructive wake interactions.

Frequency Optimization: The study underscores the importance of operating individual foils at their optimal reduced frequency (f*) to maximize energy extraction. This is particularly relevant in larger arrays where the flow conditions experienced by each foil can vary significantly due to wake interactions.

Real-World Considerations:  Translating these findings to real-world applications requires addressing challenges posed by turbulence, unsteady flow conditions, and variations in flow direction. Future research should focus on developing robust control strategies that can adapt to these dynamic conditions and maintain optimal energy harvesting performance.

Could the performance gains observed from favorable wake-foil interactions be negated or even reversed in real-world conditions with factors like turbulence and unsteady flow?

Yes, the performance gains observed from favorable wake-foil interactions in controlled laboratory settings could be significantly impacted, potentially negated or even reversed, by the complexities of real-world conditions:

Turbulence Disruption:  Turbulence can disrupt the coherent vortex structures generated by the leading hydrofoil, which are essential for the favorable interactions that enhance trailing foil performance. This disruption can lead to less predictable and potentially less beneficial wake interactions.

Unsteady Flow Velocities: Real-world flows are rarely uniform and steady. Fluctuations in flow velocity and direction can alter the trajectory and strength of wake vortices, making it challenging to maintain the precise phasing required for optimal energy extraction.

Flow Direction Variations: Changes in flow direction, common in real-world tidal and riverine environments, can further disrupt the wake structure and lead to misalignment between the trailing foil and the incoming wake, reducing efficiency.

Control System Robustness:  Maintaining the optimal performance gains observed in the study under real-world conditions necessitates robust control systems. These systems must be capable of continuously sensing and adapting to dynamic flow conditions, adjusting individual foil kinematics to mitigate the negative impacts of turbulence and flow variability.

What are the potential implications of these findings for understanding and mimicking the efficient locomotion of aquatic animals that utilize similar unsteady fluid dynamics principles?

The findings of this study hold significant implications for understanding and potentially mimicking the efficient locomotion of aquatic animals:

Bio-Inspired Propulsion Systems:  The study's demonstration of enhanced performance through precise control of wake interactions provides valuable insights for developing bio-inspired propulsion systems for underwater vehicles. By mimicking the synchronized and adaptable movements observed in fish schools, these systems could achieve significant efficiency improvements.

Understanding Fish Schooling: The study's focus on wake interaction dynamics can contribute to a deeper understanding of the complex hydrodynamic interactions within fish schools.  By analyzing how individual fish adjust their movements in response to the wakes generated by their neighbors, researchers can gain insights into the energy-saving mechanisms employed by these animals.

Optimizing Underwater Vehicle Design: The findings related to optimal inter-foil spacing and phasing can inform the design of underwater vehicles operating in formation. By optimizing the arrangement and movement of multiple vehicles, engineers can potentially reduce energy consumption and enhance maneuverability.

Developing Biomimetic Robots: The study's insights into unsteady fluid dynamics and wake control can contribute to the development of more agile and efficient biomimetic robots. These robots could be used for a variety of applications, including underwater exploration, environmental monitoring, and search and rescue operations.