## 1 Introduction
This design effectively achieves a synergistic coupling of VIV and flutter energy harvesting mechanisms, resulting in superior performance compared to individual system configurations. [PERSON] et al. [28] advanced the field by comprehensively investigating airfoil-based flutter energy harvester systems equipped with flaps. Through a multi-methodological approach that included theoretical derivations, computational simulations, and experimental validation, their study revealed an important insight: the implementation of inelastic constraint flaps fundamentally alters the vibration characteristics of the harvester. Specifically, the system transitions from flutter behavior at low velocities to VIV as the velocity increases, thereby reducing the critical flutter velocity. In a related study, [PERSON] et al. [29] conducted a detailed examination of flap installation angles, demonstrating that these angles significantly influence the vortex-shedding dynamics of the airfoil-based harvesters. Their findings confirmed that smaller installation angles consistently enhance system performance, providing valuable design guidance for future energy harvester configurations. Beyond integrating mechanical accessories, researchers have investigated the incorporation of magnetic forces as an alternative strategy to improve energy harvester efficiency. [PERSON] [30] introduced a novel airfoil-based flutter energy harvester system that simultaneously integrates piezoelectric and electromagnetic energy conversion modes. This innovative approach enables concurrent energy extraction from both structural- and flow-induced vibrations, thus substantially enhancing the system's overall performance potential. [PERSON] et al. [31] extended this concept by designing a piezoelectric-electromagnetic hybrid flutter energy harvester. By utilizing a semi-empirical nonlinear aerodynamic model and a magnetic dipole model, they observed that when magnets are positioned in close proximity, an amplitude jump occurs, significantly amplifying the output power of the electromagnetic component near a critical point. Building upon these approaches, [PERSON] et al. [32] conducted a comprehensive investigation of airfoil-based flutter energy harvesting devices, systematically analyzing the effects of various magnet installation distances through theoretical derivations, computational simulations, and experimental methods. Their findings demonstrated the profound impact of a strategic magnet arrangement, showing that an optimized configuration can reduce the critical flutter velocity by up to 80% while achieving an 82.6% increase in output power generation, marking a significant advancement in energy harvester design and performance optimization. Previous research on airfoil-based flutter piezoelectric energy harvester systems has primarily concentrated on structural design and theoretical foundations, with relatively limited scope. The mounting angle, despite being a crucial parameter in these systems, has received insufficient attention in existing literature. Given that the mounting angle is an essential installation parameter in practical applications, there is a critical need to investigate its effects systematically. To address this research gap, we employ numerical simulation methods to examine the influence of mounting angles on both the vibration dynamics and energy harvesting performance of the airfoil-based flutter piezoelectric energy harvester system. To validate our computational approach, we conduct empirical experiments using a prototype system in a specialized wind tunnel setup. This study aims to comprehensively investigate the impact of mounting angle variations on the system's vibration characteristics and energy harvesting efficiency. Based on established aerodynamic principles for determining wing angle of attack, we systematically selected three mounting angles: 3\({}^{\circ}\), 6\({}^{\circ}\), and 9\({}^{\circ}\), representing a progressive range from small to large angles.