Elastically encapsulated core annular flow

We present a combined experimental and theoretical exploration of three-layer, horizontal core–annular pipe flow, in which two fluids are separated by a deformable elastic solid. In the experiments, an elastic solid created by an in situ chemical reaction maintains the separation of the core and annular fluids. Corrugations of the elastic interface are observed, and stable pipelining, where the elastic shell created separating the two fluids remains intact, is successfully demonstrated even when the core fluid is buoyant. The theoretical model combines lubrication theory for the fluids with standard shell theory for the elastic solid. The model is used to predict the buckling states resulting from radial compression of the shell, and to explore the sedimentation of a buoyant core. The self-sculpting of the shell by buckling cannot by itself generate hydrodynamic lift owing to symmetry in the direction of flow. Instead, we demonstrate that hydrodynamic lift can be achieved by other elastohydrodynamic effects, when that symmetry becomes broken during the bending of the shell.