Theoretical and experimental investigation of a bubble collapsing near an asymmetric hydrofoil

Abstract

In the present paper, the restricted cavitation bubble dynamics near an asymmetric Joukowsky hydrofoil are investigated theoretically and experimentally. This investigation employs the conformal transformation, the image method, and the Kelvin impulse model, together with high-speed photographic experiments. The characteristics of bubble collapse deformation and bubble wall movement are analyzed qualitatively and quantitatively, and the spatial distributions of the liquid velocity and Kelvin impulse are revealed by theoretical predictions. The main conclusions include (1) the bubble collapse deformations can be divided into three typical cases: penetrating deformation (mostly occurs when γ<2 with γ defined as the bubble-hydrofoil dimensionless distance), triangular depression (mostly occurs when 2<γ<4), and arc-shaped depression (mostly occurs when γ>4). (2) The impulse acting on the bubble is governed by a point source and a point sink, which is dominant, and the impulse is inversely correlated with the bubble-hydrofoil distance, which corresponds to the experimental results. (3) The Kelvin impulse exhibits different distributions at the tail, head, and middle regions of the hydrofoil, and the impulse angle remains basically unchanged in the concave region of the asymmetric hydrofoils (i.e., the range of 240°<θz<350° with θz defined as the bubble position angle).