Gravity-driven vertical water tunnel for modeling ventilated cavity flows around axisymmetric slender body under streamwise gravitational effect

Abstract

The cavitation tunnel with controlled background pressure is a pivotal experimental setup for studying the mechanisms of cavitating flows and hydrodynamic loads on cavitating bodies. Existing recirculating cavitation tunnels predominantly feature horizontal test sections for modeling cavity flows in horizontal incoming flow and vertical gravitational acceleration and fail to meet the requirements for long-duration experiments on ventilated cavity flows. This paper introduces the unique gravity-driven vertical water tunnel (GVWT), facilitating hydrodynamic experiments on axisymmetric slender bodies with ventilated cavities in the streamwise gravitational acceleration. It elaborates high-throughput data processing method for synchronously measured high-speed camera images of cavity forms and pressure distribution from sensor arrays on model surfaces in unsteady long-duration ventilation conditions. For the ventilated cavity flow against an axisymmetric slender body with 60° cone headform at zero angle of attack, the developed partial cavity can be divided into four regimes: The sheet cavity, the combined sheet and cloud cavity, the entire cloud cavity, and the shedding cloud cavity. The mean cavity length and thickness are well-defined by the high-speed images. For the unsteady ventilated cavity due to the re-entrant jet, the Strouhal number based on cavity length and pulsation frequency of the cloud cavity equals 0.276. The mean pressure distribution in the ventilated cavity reveals a difference between the pressure within the sheet cavity and the maximum pressure in the cavity closure, which is influenced by the streamwise gravitational effect. The experimental results demonstrate that GVWT provides a novel experimental approach for understanding the physics of ventilated cavity evolution and bubbly flows under the effect of the streamwise gravitational acceleration.