Effects of multi-stage flow control structures on hydrodynamics and cavitation evolution

To optimize hydrofoil performance during multiple cavitation phases and to investigate the associated flow field characteristics, a multi-stage heterogeneous passive control strategy is proposed to balance cavitation suppression with hydrodynamic performance enhancement. Two structural optimization schemes, centralized and distributed, are investigated, and the respective effects on cavitation control and hydrodynamic performance enhancement are systematically analyzed. The centralized multi-stage control structure, incorporating optimized inter-stage spacing and structural height, significantly delays cavity shedding, reduces the drag coefficient, and improves the lift-to-drag ratio. The optimized hydrofoil achieves a maximum increase in lift-to-drag ratio of approximately 13.01%. Moreover, the centralized control structure attenuates the dominant cavitation peak frequency through sequential collaborative control, achieving a maximum frequency reduction of 6.69%. The development of sheet cavitation is effectively regulated, thereby enhancing cavity attachment and improving overall flow stability. In contrast, the distributed control strategy introduces microscale devices near the leading edge on the hydrofoil suction side, which effectively disrupt the formation and growth of the cavitation cavity and suppress the detachment of leading-edge attached bubbles. Additionally, staged intervention across multiple cavitation phases reduces the formation of free bubbles during cavitation collapse and shedding, thereby further mitigating cavitation intensity. The optimized multi-stage configurations consistently outperform the single-stage structure across multiple metrics, including cavitation delay, fluctuation suppression, pressure stability, and secondary cavitation mitigation.