This paper investigates a flow-induced vibration energy harvester comprising a piezoelectric beam (piezo-beam) installed within a hollow circular cylinder. Under the flow excitation, the energy-harvesting system including the cylinder and the piezo-beam vibrates and generates electricity. A lumped parametric model incorporating the fluid-structure interaction (FSI) is developed to evaluate the performance of the proposed energy harvester. Based on the theoretical analysis, several guidelines on the design and optimization of the proposed energy harvester are provided. Subsequently, a numerical model is used to simulate the FSI between the proposed system and the external flow field. Finally, a physical prototype is fabricated and an experiment is conducted to test the actual performance for validation. The theoretical analysis results are verified by the numerical and experimental results.