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<p>Cavitation technology is a cornerstone of many industrial applications, but its use is often constrained to submerged environments. Co-flow cavitation jets overcome this limitation. It generates intense cavitation by injecting a high-speed liquid jet into a concentric, lower-speed flow, which offers transformative potential for high-efficiency manufacturing in ambient air. However, the fundamental fluid dynamics governing their performance, particularly the role of outer nozzle geometry, remain insufficiently explored. This study combined high-speed imaging and validated numerical simulations to investigate the flow physics of co-flow cavitation jets. Our results revealed three distinct flow regimes: an Initial Cavitation Zone I, a Mix-and-Shear Zone II, and a Turbulent Diffusion Zone III. We demonstrate that Kelvin-Helmholtz instabilities at the interface between the inner and outer flows are the dominant mechanism driving shear cavitation and are paramount to the jet’s intensity. Critically, we identify the clearance between the inner and outer nozzles as a controlling parameter. Insufficient clearance prevents the outer flow from effectively shielding the inner jet, leading to premature energy dissipation via aerodynamic atomization. Conversely, excessive clearance delays the onset of KH instabilities, weakening the resulting cavitation. An intermediate clearance was found to produce the most stable and intense cavitation. These findings provide critical design principles for optimizing co-flow nozzles, advancing applications in surface treatment, material removal, and fatigue strengthening under non-submerged conditions.</p>

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Flow dynamics and nozzle clearance effects in non-submerged co-flow cavitation jets

  • 期刊论文

  • 发表日期：

    2026年5月9日

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  • Han Ge,
  • Jiawang Chen,
  • Chizhong Wang

摘要

Cavitation technology is a cornerstone of many industrial applications, but its use is often constrained to submerged environments. Co-flow cavitation jets overcome this limitation. It generates intense cavitation by injecting a high-speed liquid jet into a concentric, lower-speed flow, which offers transformative potential for high-efficiency manufacturing in ambient air. However, the fundamental fluid dynamics governing their performance, particularly the role of outer nozzle geometry, remain insufficiently explored. This study combined high-speed imaging and validated numerical simulations to investigate the flow physics of co-flow cavitation jets. Our results revealed three distinct flow regimes: an Initial Cavitation Zone I, a Mix-and-Shear Zone II, and a Turbulent Diffusion Zone III. We demonstrate that Kelvin-Helmholtz instabilities at the interface between the inner and outer flows are the dominant mechanism driving shear cavitation and are paramount to the jet’s intensity. Critically, we identify the clearance between the inner and outer nozzles as a controlling parameter. Insufficient clearance prevents the outer flow from effectively shielding the inner jet, leading to premature energy dissipation via aerodynamic atomization. Conversely, excessive clearance delays the onset of KH instabilities, weakening the resulting cavitation. An intermediate clearance was found to produce the most stable and intense cavitation. These findings provide critical design principles for optimizing co-flow nozzles, advancing applications in surface treatment, material removal, and fatigue strengthening under non-submerged conditions.