Vendredi 16 mai à 11h00, salles des séminaires IRPHE
Many natural and industrial systems involve multi-phase flows of gas, liquid and solid particles. However, a clear comprehension of the underlying physical mechanisms remains a challenge. In particular, the link between the processes at the microscale – such as grain size, shape, asperities – and the behavior at larger scale (bubble velocity, interactions, emergence of instabilities...) is still not fully understood. Based on laboratory experiments, we investigate the dynamics of bubble rise in Newtonian fluids and in dense granular suspensions.
In the first part, we compare the dynamics of a single bubble rising in a Hele-Shaw cell. For Newtonian fluids, we analyze the evolution of the bubble speed, aspect ratio and drag coefficient for two different configurations: (i) during the transition from the viscous to the inertial regime and (ii) in a Hele shaw cell subject to various inclination angles with respect to gravity. We then focus on the rise of a single bubble in a density-matched suspension in the low Reynolds number regime. We quantify the vertical velocity as a function of the particle volume fraction. Surprisingly, bubbles rise faster in suspensions as compared to particle-less liquids of the same effective viscosity.
In the second part, we study a 3D scenario: the emptying of a bottle – an everyday example of two-phase fluid mechanics. While the alternation between rising bubbles and downward liquid jets begins to be well understood, we propose to further complicate the phenomenon by studying the draining of suspensions. The main objective of our experiments is to understand the interactions between the bubbles, the fluid and particles during bottle drainage. To achieve this, we use different suspensions and sizes of draining hole. We exhibit counter-intuitive behaviours such as the flow rate being constant during the draining, while the speed of the liquid free surface can exhibit different regimes if enough particles are stuck in the bottle.