## 5 Conclusions  
This study systematically investigates the performance characteristics of airfoil-based flutter piezoelectric energy harvesting systems at the installation angles of 3\({}^{\circ}\), 6\({}^{\circ}\), and 9\({}^{\circ}\), using both numerical calculations and experimental methods. Taking the 0\({}^{\circ}\) configuration as the baseline, a detailed analysis is conducted to evaluate the effect of installation angle on system performance. The research, while conducted under controlled conditions, identifies several critical aspects that warrant further investigation for practical applications, including the influence of environmental factors (temperature and humidity) on energy harvesting efficiency, system resilience to disturbances in actual wind fields, and the impact of structural and material fatigue on long-term performance. Although these practical considerations require additional research, this study successfully establishes the fundamental relationship between installation angle and system performance under controlled conditions, providing a solid theoretical foundation for practical implementations. The main conclusions are as follows:  
1. The installation angle is a crucial parameter influencing the critical flutter velocity of the airfoil-based piezoelectric energy harvester system. A clear inverse relationship exists between the installation angle and critical flutter velocity, with the latter decreasing from 7.8 m/s at 0\({}^{\circ}\) to 6.3 m/s at 9\({}^{\circ}\). This systematic reduction in critical velocity can be attributed to enhanced initial lift generation at higher installation angles, which facilitates the earlier onset of flutter oscillations. 2. Moderate installation angles (3\({}^{\circ}\) and 6\({}^{\circ}\)) yield optimal energy harvesting performance. The system achieves maximum efficiency at a 3\({}^{\circ}\) installation angle, producing a peak output voltage of 12.0 V and power output of 0.58 mW, marking a substantial improvement over the baseline configuration at 0\({}^{\circ}\) (10.9 V, 0.48 mW). This enhanced performance stems from the development of favorable asymmetric flow field characteristics at moderate angles, enabling more efficient energy extraction from the airflow. 3. At higher installation angles, particularly at 9\({}^{\circ}\), significant performance degradation occurs. Although this configuration achieves the lowest critical flutter velocity, it exhibits markedly reduced performance metrics (7.9 V voltage, 0.25 mW power). This deterioration is primarily due to the premature aerodynamic stall and persistent flow separation, highlighting a fundamental trade-off between reduced critical flutter velocity and maintained aerodynamic stability. 4. Installation angle adjustment represents an effective and practical approach to optimizing airfoil-based flutter energy harvesters, particularly in low-speed wind conditions. However, successful implementation necessitates careful consideration of the balance between reducing critical velocity and avoiding stall conditions. The results suggest that optimal performance can be achieved with moderate installation angles around 3\({}^{\circ}\) to 6\({}^{\circ}\), providing valuable guidance for practical applications. Figure 14: Energy collecting and physical device of powering directly. (**a**) schematic diagram; (**b**) physical device. **Author Contributions:** R.T.: Writing--original draft, preparation, methodology, and software. D.L. : Formal analysis and writing--review and editing. Y.W. : Formal analysis and writing--review and editing. Z.Y. : Conceptualization and writing--original draft, preparation, Validation, methodology, and software. All authors have read and agreed to the published version of the manuscript. **Funding:** This research was funded by the National Natural Science Foundation of China (Grant No. 52165010), and Guangxi Science and Technology Major Project (Grant No. GuiKeAA24206038). **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable.