Internal Flow Characterization of Ventilated Partial Cavitation Using Particle Image Velocimetry

Abstract

Understanding the gas leakage mechanisms of a Ventilated Partial Cavitation (VPC), an artificial air pocket formed by injecting air behind a flow separation device in water flow, is important for its potential application to drag reduction during ship operations. While the gas leakage mechanism of VPC involves the coupling of both internal air phase and external water phase flows, the literature lacks characterization of internal flow. Our study provides the first experimental investigation of the internal flows of VPC formed by air injection past a backward-facing step. Planar Particle Image Velocimetry (PIV) with fog particles as tracers is employed to perform flow visualization and time-resolved PIV to provide the internal flow characterization of VPC. Distinctive characteristics are observed in each regime, both in instantaneous and time-averaged senses. Further, the analogy between internal flows of VPC and a single-phased flow over a backward-facing step is suggested to explain the behaviors of VPC including the cavity lengths and the effect of flow parameters on each regime and further on the transition across regimes.