Mechanisms of cloud-cavitation control by semis-pherical micro-structures on a three-dimensional hydrofoil: An experimental study

Cloud cavitation is a highly unsteady and destructive phenomenon that can severely affect the performance, stability, and structural durability of hydrodynamic systems. This study presents a comprehensive experimental investigation into controlling cloud cavitation over a three-dimensional Clark-Y hydrofoil using semi-spherical surface microstructures (SMs). A parametric evaluation was conducted to examine how protrusion diameter, height, and location influence boundary-layer development and re-entrant-jet dynamics, thereby modulating cloud-cavitation shedding. All experiments were performed under identical hydrodynamic conditions in a water tunnel (Re = 7 × 105, σ = 0.8, and α = 8°). The results demonstrate that SMs affect cavitation through two primary mechanisms: leading-edge SMs stabilize the boundary layer and attached cavity, delaying separation, whereas trailing-edge SMs weaken the re-entrant jet and reduce large-scale cavity shedding. Quantitatively, increasing the diameter of trailing-edge SMs from 1 to 2 mm reduced cavity length by 8%–9.4% and increased shedding frequency by 6%–13%. At the trailing edge, a height of 0.25 mm provided optimal control (23% reduction in cavity length, 22% increase in frequency), while larger heights diminished effectiveness. Conversely, increasing SM height to 1 mm at the leading-edge improved performance (16% reduction in cavity length, 8% increase in frequency). The combined configuration of SMs at both the leading and trailing edges yielded the strongest control, achieving a 53% reduction in cloud cavity length by simultaneously stabilizing the upstream flow and disrupting re-entrant jet formation.