V0070: FARAMIX: Mixing induced by surface waves in stratified fluids

Andrés Castillo-Castellanos, LRC-MESO, Centre Borelli, ENS Paris Saclay, Université Paris Saclay
Benoît-Joseph Gréa, CEA, DAM, DIF; Université Paris Saclay, CEA, Laboratoire Matière en Condition Extrême
Antoine Briard, CEA, DAM, DIF
Louis Gostiaux, LMFA UMR 5509 CNRS, Université de Lyon, École Centrale de Lyon
DOI: doi.org/10.110...
Standing waves can be observed at the interface between two miscible fluids of smalldensity contrast (liquid-liquid) when subject to a time-periodic vertical accelerationvia the Faraday instability. A turbulent mixing zone may develop, grow in sizeand eventually saturate when the mixing layer is no longer excited by the periodicforcing. Depending on the control parameters, the final transition to turbulence canbe explained by breaking process of Faraday waves.For this work, we study the influence of a free-surface (liquid-gas) near the miscibleinterface using the experimental measurements of the FARAMIX2 project. Becauseof the small density contrast, surface waves may drive the interface, but the interfacehas no effect on the free-surface. This leads to two additional scenarios for the tran-sition to turbulence. In the first one, internal waves are excited (indirectly) by thesurface waves through a parametric instability. In the second one, turbulent mixingis controlled directly by large-amplitude droplet-ejecting surface waves.The complex fluid dynamic process during drop ejection and bursting is simulatedusing two-phase DNS with a volume-of-fluid method implemented in Basilisk. Ifthe surface waves are sufficiently close to the interface, they can eat into stratifiedfluid, effectively pushing the interface downwards until reaching an asymp-totic state. Finally, we present a model based on conservation laws to predict theacceleration rate and the final position of the interface.
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