Volume oscillations slow down a rising Taylor bubble

Taylor bubbles -- volumes of gas rising in vertical tubes with an equivalent spherical diameter greater than the diameter of the tube -- are often encountered in the energy, chemical and oil industries. In a recent paper (Zhou & Prosperetti, J. Fluid Mech. 920, R2, 2021) we have shown that, artificially constraining the bubble diameter by means of a porous surface coaxial with the tube, the rising velocity of the bubble can be considerably increased. This result establishes a connection between the bubble rising velocity and the drainage liquid flow in the film separating the bubble from the tube wall. In the present work we find by numerical means that, if the bubble is forced to execute small-amplitude volume oscillations, subtle non-linear processes involving liquid inertia and the displacement of stagnation points on the bubble surface cause the liquid film to become considerably thinner than for an ordinary constant-volume Taylor bubble. Correspondingly, the bubble rise considerably slows down and very nearly stops.