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What can ultrasounds tell us on aeration phenomena
Aeration sounds like a very familiar process. We all have an experience of making bubbles in a liquid. However, despite abundant literature on foaming and fragmentation, there are still open questions on how bubbles are entrained by a flow, sliced by an eddy, or even simply how they pop at a surface. Even determining what is the key characteristic of the liquid that will matter is not that obvious. Of course, interfaces will play a role. Does it mean that everything is dictated by surface tension ?
In this talk, we will show that ultrasounds can be a good tool for investigating the aeration of liquids : they allow us to get real-time information on the bubble population in a turbulent flow. We will present experimental results on the particular case of lubricating oils. When a gear rotates in a bath of oil, it entrains bubbles. The level of aeration depends on the speed of rotation, but it is also very sensitive to the formulation of the oil. We will show how oils with different additives lead to different levels of aeration, and how the results correlate with physico-chemical measurements.