The transformation of cavitation modes during the throttling process in variable-area cavitation Venturi (VACV) tubes is critical for flow regulation accuracy and may significantly impact operational safety. However, the underlying mechanisms governing cavitation mode transitions remain poorly understood. This study combines experimental observations and large eddy simulation to investigate unsteady flow dynamics and cavitation phenomena in a VACV tube, aiming to elucidate the evolutionary characteristics of cavitation during throttling. Additionally, the effects of key operational parameters on cavitation development and oscillation were systematically analyzed. Investigations were conducted across varying throat areas and cavitation numbers, revealing two distinct cavitation patterns: attached cavitation and detached cavitation. Attached cavitation exhibits higher oscillation frequencies (250–283 Hz, St = 0.38–0.43) and shorter lengths, primarily driven by the periodic evolution of large-scale vortex structures. In contrast, detached cavitation shows lower oscillation frequencies (157–250 Hz, St = 0.31–0.38) and significantly greater lengths, largely influenced by flow separation effects. Numerical simulations reveal periodic variations in both cavitation morphology and flow field distribution along the flow direction, arising from the cyclic development of recirculation zones toward the throat region. These recirculation zones generate varying shear interactions with the mainstream flow, including stratified, shear, and intense shear flows. A comparative analysis of flow field characteristics under different throttling depths demonstrates that the plug cone induces fluid–structure interactions near the wall, triggering a transition from attached to detached cavitation. This finding provides valuable insights for optimizing the design and performance of VACV tubes in flow control applications.
Long et al. (Wed,) studied this question.