Fluid Dynamics of Bubbles Rising in Viscoelastic Liquids
Another interesting feature lies in the fact that the flow pattern in the wake of a bubble rising in a viscoelastic liquid is quite different from that in a Newtonian liquid. Specifically, in the former case for certain parameter values, there is an additional vortex ring in the surrounding flow corresponding to the existence of a negative wake. This, in a way, is similar to the case of a jet engine where the thrust in the forward direction is generated by ejecting gases at a fast speed in the reverse direction (Newton’s third law); the difference being that in the present study the negative wake arises simply due to the viscoelasticity of the fluid. We are using direct numerical simulations and experiments to understand this process.
Figure. The trace of the configuration tensor A around a rising bubble, trA, from direct numerical simulations, showing that the trace is maximum at the trailing end of the bubble (left illustration). Also notice that the trailing end of the bubble is cup-shaped and the wake is negative as the velocity vectors in the wake point away from the bubble (right illustration).