Experimental investigation of combined active-passive control on cavitating flow around a three-dimensional hydrofoil

• We combined vortex generators with air injection on a NACA 0015 hydrofoil and achieved significant reductions in cloud cavitation intensity and unsteady loads across cavitation numbers from 3.7 to 1.8. • An air-injection rate of 2 Liters per minute (Cq = 6.7 × 10⁻⁴) proved optimal, effectively minimizing vapor fraction and force fluctuations without causing excessive ventilation. • Our image analysis shows the hybrid approach reduced cloud cavity length by up to 82% at σ = 1.8, breaking up large coherent clouds into smaller, less damaging ventilated cavities. • Advanced modal analysis (POD and DMD) revealed that air injection breaks down the dominant shedding mode into multiple weaker modes, stabilizing the cavitation behavior. • By combining high-speed imaging, spectral analysis, and modal decomposition, we demonstrate a practical method to reduce cavitation in hydrofoils useful in turbomachinery. Motivated by realistic operating conditions, a three-dimensional NACA0015 hydrofoil was investigated for cavitation control using vortex generators and air injection. To the authors’ knowledge, this is the first study to simultaneously compare cavitation control using vortex generators assisted with multiple air-injection rates. To assess the effectiveness of cavitation control, three configurations were examined: a plain hydrofoil, a hydrofoil equipped only with a vortex generator, and a hydrofoil furnished with vortex generators combined with air injection. Experiments were conducted at a Reynolds number of 5.5 × 10 5 and an angle of attack of 12°, covering cavitation numbers from 3.7 (inception) to 1.8 (cloud cavitation), with air supplied between 1 and 3 liters per min (L/min). The analysis relied on synchronized force measurements and high-speed imaging, combined with proper orthogonal decomposition, dynamic mode decomposition, fast Fourier transform, and wavelet analysis. At σ = 1.8, the combined vortex-generator and air-injection strategy operated at 2 L/min reduced the time-averaged cloud-cavity length by about 87% compared to the plain hydrofoil and by about 85% relative to the vortex-generator-only configuration. The vortex-generator-only configuration was effective mainly in the sheet and partial cavitation regimes, whereas the combined vortex-generator and air-injection configuration was more robust in suppressing cavitation activity and further shortened the cavity length. A combined vortex generator and air injection strategy suppresses cloud cavitation, achieving up to ∼87% reduction in cavity length.