The gap size effect on leakage flow and cavitation in the clearance of a 2D hydrofoil: high-speed visualization and velocity measurements

Abstract

In the study, tip-clearance cavitation inception and development was studied in the gap between an end face of a NACA0022-34 hydrofoil and a transparent sidewall of a test channel. The experiments were carried out for the attack angles of 3° and 9° and the gap width of 0.4 to 0.8 mm under various flow conditions on the cavitation number. In order to observe the tip-clearance cavitation inception and its dynamics, a high-speed visualization was applied. The leakage flow velocity was measured inside the clearance by a modified PTV technique. It was shown that unsteady dynamics of the primary cavity on the foil suction side affects the leakage flow direction and the gap cavitation evolution. An increase of the gap width causes the gap cavitation to be initiated at higher cavitation numbers.