## 4 Conclusions  
This study has successfully introduced a compact, efficient, and robust flow energy harvester, employing a novel flow control method featuring a cylindrical spoiler structure positioned at the trailing edge of the oscillating foil:  
1. A notable enhancement of 19.26% has been achieved in the efficiency of the oscillating foil with the cylindrical spoiler structure at the trailing edge, utilizing a cylinder diameter of 11.0% of c, a transverse spacing of 0.5% of c, and a longitudinal spacing of 0.
2. It is crucial to highlight that an increase in cylinder diameter corresponds to an augmentation in energy harvesting efficiency, although with diminishing returns.
3. The variation in transverse spacing demonstrates a non-linear relationship with the energy harvesting efficiency of the oscillating foil. Within the examined range of 3.5%  
Figure 17: Energy harvesting efficiency of the oscillating foil with/without a cylindrical spoiler structure at the trailing edge for different pitching amplitudes.  
to 65.5% of the chord length, the cylindrical spoiler structure has shown no positive impact on the energy harvesting performance. Practical applications should carefully consider transverse spacing based on specific requirements.
4. Increasing the longitudinal spacing of the cylinder results in the trailing edge cylinder deviating from the mid-chord, enhancing the energy harvesting performance during the first half-cycle while causing a corresponding decrease in the second half-cycle. However, the overall integrated energy harvesting performance remains superior to that of the original foil without the cylinder. It is important to note that the degree of improvement diminishes as the longitudinal spacing of the cylinders increases.
5. The innovative flow control technique, incorporating a cylindrical spoiler structure at the trailing edge of the oscillating foil, has proven highly effective in enhancing energy harvesting performance across various reduced frequencies, relative heaving amplitudes, and pitching amplitudes.  
The findings of this study provide valuable insights for the design, optimization, and adaptability assessment of oscillating foil energy harvesting devices. We posit that this flow control method opens new avenues for the development of more efficient and practical oscillating foil devices. Future research endeavors could focus on conducting additional experimental measurements to evaluate and address uncertainties associated with numerical simulation calculations.  
Conceptualization, F.Z. and D.Z.; methodology, F.Z.; software, H.L.; validation, F.Z., H.L. and Q.Z.; formal analysis, F.Z.; investigation, H.L.; resources, Q.Z.; data curation, F.Z. and H.L.; writing--original draft preparation, F.Z. and Q.Z.; writing--review and editing, F.Z. and D.Z.; visualization, Q.Z.; supervision, Y.X. and D.Z.; project administration, D.Z.; funding acquisition, Y.X. All authors have read and agreed to the published version of the manuscript.  
This research was funded by National Natural Science Foundation of China (grant number: 11872294).  
Data Availability Statement: Data are contained within the article.  
The authors declare no conflict of interest.