Direct numerical simulation of the flow over a spherical bubble in a turbulent pipe flow

This work aims at investigating, by means of a direct numerical simulation, the flow over a clean spherical bubble fixed on the axis of a turbulent pipe flow. The simulation is performed by means of a parallel unstructured symmetry-preserving formulation on a mesh of 5.4M cells. The main features of the turbulent flow are described by analyzing the time-averaged data collected over a significant period of time. The numerical results conclude that the bubble generates a wake, similarly to the case of a solid sphere, however, it differs in the fact that the fluid slips through the surface of the bubble instead of stopping, thus, no boundary layer is created. Moreover, due to viscosity, a transfer of momentum from the fluid surrounding the bubble to the fluid inside of it is produced. This transfer of momentum generates a turbulent toroidal vortex inside the bubble. In consequence, two short recirculation zones are found at the extremes of the bubble’s diameter, while in between, the axial velocity inverts its sign.