Numerical Investigation of Cavitation Dynamics and Hydraulic Flip Transition in an Internal Nozzle

This paper presents a numerical investigation of the cavitation dynamics and hydraulic flip transition in a rectangular nozzle using an Eulerian–Eulerian two-fluid model. The Schnerr–Sauer cavitation model was employed, with its key parameter—the initial bubble number density—set to 1014 m−3 based on experimental data to match the incipient cavitation and regime transition pressures accurately. Combined with a modified Reynolds-averaged Navier–Stokes turbulence model that incorporated the bubble-induced viscosity, this approach significantly improved the prediction accuracy of the mean flow field. The results revealed the quasi-periodic evolution from sheet to cloud cavitation, showing that the dominant frequency of cavity oscillations decreased with increasing inlet pressure. In contrast, the growth of sheet cavitation was the primary source of liquid turbulent kinetic energy. Furthermore, the complete transition sequence from super-cavitation to hydraulic flip was captured, elucidating the underlying vapor–air mixing mechanism. Analysis indicated that the hydraulic flip establishment time decreased sharply with the pressure before plateauing. In contrast, its thickness remained largely insensitive to the pressure and was governed by the upstream geometric configuration. The findings provide a calibrated and validated numerical framework for understanding complex cavitation mechanisms and optimizing spray system designs.