Examination of cavity type, closure mechanism, and gas entrainment rates of 2-D ventilated cavities behind a bluff body

Formation and sustenance of ventilated partial and supercavities is essential to achieve reduced skin-friction drag in underwater supercavitating vehicles. Understanding the flow physics at the cavity closure region and the relationship to cavity shape/topology and stability is crucial to maintaining stable cavities. In this work, ventilated partial- and super-cavities in the wake of a bluff body are studied in the Michigan 8-inch water tunnel. Cavity formation, closure and gas transport are investigated using high-speed videography and time-resolved X-ray densitometry. The gas fraction in the ventilated cavity is measured and cavity closure mechanisms for a range of Reynolds number, Froude number, and air injection rates are mapped. From the measured void-fraction flow fields, gas transport analysis is performed to understand the closure mechanisms responsible for a given condition.