Jean-Philippe Matas (LMFA Lyon) - Bubble dynamics: from single bubble to bubble cloud

I will focus on two distinct experiments in this seminar. The first one is an experiment in which we have studied the dynamics of a single bubble trapped close to the axis of a horizontal solid body rotation flow. I will show how  bubble deformation and break-up can be controlled and modelled. We have also studied how this dynamics was impacted when a surfactant was introduced in the liquid. I will discuss in particular the results obtained when the surfactant concentration is lowered below the critical micelle concentration.

The second part of my presentation will address the simple question of the size of the bubble cloud created by a jet plunging vertically into a reservoir. A series of experiments have been carried out over a wide range of scales (from mm scale to several meters in height of fall). These results evidence that two regimes exist: a regime in which the bubble cloud size is controlled by momentum conservation within the cloud, as initially proposed by Clanet & Lasheras (1997) ; and a regime for larger jets where buoyancy controls the cloud size. I will discuss the border between these regimes, and  which dimensionless groupings control this problem.