Investigation on turbulence in the vicinity of liquid-liquid interfaces – Large eddy simulation and PIV experiment

Abstract

In this work, the turbulence in the vicinity of the liquid-liquid interfaces in an incompressible interfacial flow is investigated numerically and experimentally. A new large eddy simulation formulation is employed where all the subgrid scale (SGS) terms appearing in the filtered governing equations are closed by a volume of fluid-based Approximate Deconvolution Model (ADM-VOF) (Saeedipour et al., 2018). In this structural turbulence modelling approach, the SGS terms of stress tensor and surface tension in the Navier-Stokes equations, as well as the interface dynamics in the VOF transport equation, are mathematically reconstructed from the resolved scales. An oil-water benchmark experiment was designed for validation purposes where an oil layer is poured on the top of the water into which a submerged turbulent jet is injected and interacts with the oil–water interface. The interactions of the turbulence with the liquid-liquid interfaces are then studied by shadowgraphy visualization and time-resolved PIV measurement. Two sets of LES were performed using the ADM-VOF and a conventional LES model based on eddy-viscosity approach. The statistics of interfacial turbulence including velocity fluctuations and interface dynamics are analyzed and compared with the ones obtained from the experiment. The results reveal that in the interface vicinity the ADM-VOF approach, which reconstructs more turbulent scales and includes the SGS terms of turbulence-interface interactions, is of superior performance in predicting the energy spectra and statistics of turbulence. Far from the interface no particular difference between the LES models was observed. In addition, the temporal average of the interface motion as well as the evolution of the interfacial area is studied. While both models predict the averaged temporal evolution of the interface similarly, the ADM-VOF revealed its potentials for high fluctuating regions as it accounts for the effect of SGS term interface dynamics. This study provides a perspective for connecting the interfacial turbulence to metallurgical aspects of the continuous casting process.