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Hydroelastic Effects on Energy Harvesting of a Semi-active Flapping-foil Mechanism

Jalali Zeidanlu, Mohammad | 2021

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 54245 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Ebrahimi, Abbas
  7. Abstract:
  8. The purpose of this study is to investigate a flapping hydrofoil with semi-active kinematics for energy harvesting and evaluate the effect of different dynamic parameters and structures on its performance. The turbulent flow field with Re = 5 × 105 around a NACA 0015 hydrofoil is simulated by URANS method using commercial software and the dynamics of the oscillating hydrofoil is modeled as a mass-spring-damper set in combination with the fluid solver. The sliding mesh method is used for the pitching motion of the hydrofoil with a reduced frequency of 0.14 in combination with the dynamic mesh method for Transitional motion. Initially, the oscillating hydrofoil was considered as a single section without the effects of structural flexibility, in which case the elastic turbine model consisted of a linear spring and damper that provided only the degree of freedom of movement of the hydrofoil. As a result of measuring different values for this combination, a case with a power coefficient of 0.93 and an efficiency of 41% has been selected as the optimal one. In the next step, a torsion spring and damper are added to the system to study the effect of flexibility in the span-wise direction. The purpose of using this elastic compound was to model a hypothetical section between the middle and the tip of a flexible wing in the span-wise direction. Linear spring and damper coefficients have been selected according to the amount of flexural flexibility and torsional spring and damper coefficients have been selected according to the desired torsional deformation size. Based on the results, the alignment of the transfer speed and the force applied by the fluid to the foil increases the absorption power from the flow, but due to the larger transmission range in these conditions, the efficiency of the system also decreases. In this case, the maximum power coefficient is 1.44, which is associated with an efficiency of 14%. Also, different values of flexibility have led to a change in the pattern of movement of different sections so that the torsion and transmission amplitudes are reduced from 62.7 degrees and 0.77 c for the rigid wing to 47.45 degrees and 0.54 c for the flexible wing, respectively. Changes in the motion pattern change the performance of the flapping foil so that the power coefficient and energy efficiency decrease from 0.36 and 18% for a rigid wing (non-optimal) to 0.11 and 8.1% for a flexible, respectively
  9. Keywords:
  10. Numerical Simulation ; Energy Harvesting ; Flapping Foils ; High Reynolds Number ; Hydroelastic Effect ; Semiactive Kinematics

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