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01 Bubbly Flow by Air Injection on an Inclined Hydrofoil

Physics of Fluids 33, 042209 (2021); DOI: 10.1063/5.0043221

In this work, flow features resulting from air injection through a hole on an inclined hydrofoil in a free stream flow are characterized. The experiments were carried out in a cavitation tunnel at the Chungnam National University. The hydrofoil was oriented at different angles of inclination in the test section with water flowing at the free stream velocity, 3, 5 and 7 m/s (Fn=30~70). The air jet emanating from the hole on the inclined hydrofoil along the streamwise direction, at various air injection rates (Cq) was characterized by high-speed imaging. Geometric features of the air jet, such as jet width, angle, effective diameter and thickness are measured from the high-speed images. A power-law relation is shown to exist between the non-dimensional geometric features of the jet and the non-dimensional parameters, Re, Fn, Cq. Depending on the Froude number (Fn) and non-dimensional air injection rate (Cq), several jet domains such as unstable jet, cloudy puff, buoyant-bifurcating jet, and stable-buoyant jet domains were observed upon air injection at Rn~1000 for various hydrofoil inclinations.

02 Experimental Investigation of Artificial Supercavitation

Physics of Fluids 31, 052106 (2019); DOI: 10.1063/1.5092542

Experimental investigation on drag characteristics and flow physics of ventilated supercavitating objects with different body shapes were conducted at the CNUCT. The test model consists of a disk-type cavitator with two different fore bodies (slender and blunt shape) and three different rear bodies (flat, shrinkage, and expanded shape). The drag forces acting on different body-combinations in fully wetted conditions are measured and the results show that the drag coefficients strongly depend on the body shapes. It explains in detail through particle image velocimetry measurements. The drag characteristics are systematically examined over a broad range of ventilation rates. The formation and the drag characteristics of the foamy and clear supercavity flow are investigated for different Froude number conditions. The results reveal that the drag of the blunt fore body is smaller than that of the slender fore body in foamy cavity conditions. In ventilated supercavity conditions, supercavity shapes according to Froude numbers are examined and corresponding effects on drag characteristics are analyzed. The results show that the drag coefficients of the models with the expanded rear body are larger than that of models with the flat and shrinkage rear bodies until the cavity covers the body.

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03 Coherent Structure of Turbulent Cavitating Flow

Fluids 2020, 5(4), Invited; DOI: 10.3390/fluids5040198

In many practical submerged objects, various types of cavitation such as bubble, sheet, and cloud cavitation occur according to flow conditions. In spite of numerous theoretical, numerical, and experimental studies, there are still many problems to be solved such as induced noise and damage potential due to cavitation. In this paper, an experimental investigation on coherent structures and induced noise characteristics of partial cavitation on a two-dimensional hydrofoil is presented. Experiments that focused on the dynamics of cavitation clouds were conducted in a cavitation tunnel. Using high-speed visualization, the series process consisting of inception, growth, and desinence of the partial cavity was investigated. The noise generated during the process was also measured, and the correlation with the cavity pattern was examined. The results show that the periodic behavior of cavitation clouds is directly reflected in the noise characteristics. In addition, the visualization of coherent structures within the sheet and cloud cavity provides a qualitative understanding of hairpin vortices and their packets, which play a dominant role in turbulent cavitating flows.


Dept. of Naval Architecture and Ocean Engineering, College of Engineering, Chungnam National University,

99 Daehak-ro, Yuseong-gu, Daejon, 34134, KOREA