斜め平板下を上昇する球形気泡群によるクラスタ形成過程の実験的解析

Abstract

The motion of mono-dispersed spherical bubbles rising along an inclined flat plate is investigated experimentally. An inclination angle of the flat plate is changed to control the bubble Reynolds number set to be 100. As experimental conditions, the number density of bubbles and the boundary condition on the bubble surface (free-slip and no-slip conditions) are varied, and their effects on the motion of the bubbles are analyzed. MgSO4 solution and Triton X-100 solution are used to achieve free-slip and no-slip bubble surfaces, respectively. In both cases, bubble coalescences are almost inhibited. When the number density of bubbles becomes higher and the rising velocity along an inclined flat becomes slower, the bubbles tend to be horizontally arranged in lines and such arrangements pile up to the bubble cluster. The radial pair distribution function and the conditional average of the relative velocity of two bubbles are calculated to evaluate the spatial distribution and bubble-bubble interaction quantitatively. The results shows that the bubble pair configuration of next to each other frequently appears; a horizontally-oriented (side-by-side) configuration is stable compared to a vertically-oriented (tandem) one. A qualitative tendency of the clustering motion is similarly confirmed when the no-slip condition is imposed on the bubble surface, however, quantitative differences occur due to the difference in the wake structure between these two conditions.