Experimental investigation of bubbly flow by air injection on an inclined hydrofoil

Flow features resulting from air injection through a hole on an inclined hydrofoil in a free stream flow are characterized in this work. The experiments were carried out in a cavitation tunnel at the Chungnam National University. The hydrofoil was oriented at angles of inclination, α=±3.5° and 0°, in the test section with water flowing at the free stream velocity, V∞= 3, 5, and 7 m/s (Froude number, Fn∼ 30–70). The air jet emanating from the hole on the inclined hydrofoil along the streamwise direction [Reynolds number of air, Reair∼O(103)], at various air injection rates, Cq, was characterized by high-speed imaging. Geometric features of the air jet, such as jet width, w, jet angle, β, jet effective diameter, deff, and jet thickness, t, 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, Reair,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 Reair∼O(103) for various hydrofoil inclinations.