Unsteady dynamics of Taylor bubble rising in vertical oscillating tubes

The present work deals with the motion of a Taylor bubble rising through vertical oscillating pipes. The aim is to perform a more detailed and quantitative study of this unsteady flow, still seldom addressed in the literature. The investigation is restricted to high Reynolds numbers to understand inertia effects. Experimental results are provided for two different configurations: (1) pipes with two different inner diameters (9.8 mm and 20 mm) filled with water, (2) the thinner pipe (D=9.8mm) filled with four low viscous fluids. So the Bond number Bo based on the steady rise velocity varies from 13 to 57, where the effects of surface tension can be considered. The bubble trajectory is tracked by using a high-speed video camera. The average terminal and fluctuating velocity, as well as the phase shift with the oscillating plate are obtained by using image processing. The main results show that for weak acceleration, the mean velocity decreases with the relative acceleration as the fluctuating velocity increases in proportion to this acceleration. Beyond a critical relative acceleration, the average velocity increases and the fluctuating velocity increase seems to slow down. Additionally, comparisons are made with experimental results of Brannock and Kubie [Brannock, D., Kubie, J., 1996. Velocity of long bubbles in oscillating vertical pipes. Int. J. Multiphase Flow 22, 1031-1034] and numerical results of Clanet et al. [Clanet, C., Heraud, P., Searby, G., 2004. On the motion of bubbles in vertical tubes of arbitrary cross-sections: some complements to the Dumitrescu Taylor problem. J. Fluid Mech. 19, 359-376].