Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

The numerical simulation of gas-liquid flows is a challenging task, when dynamics of systems at industrial scales are considered. A significant contribution to this complexity arises due to the coexistence and interaction of different flow morphologies, such as bubbly and stratified flows. One of the phenomena is the entrainment of small gas bubbles into the liquid bulk at a large-scale gas-liquid interface in regions of high shear rates. In order to capture such phenomena and make reliable predictions, hybrid modelling approaches are used. One of those is the morphology adaptive multifield model developed by Meller et al. (2021), which combines an Euler-Euler method with an algebraic Volume-of-Fluid method for disperse and continuous gas structures, respectively. The interfacial drag coupling is adapted to the local grid resolution at the interface location (Meller et al., 2022). In such a modelling framework, morphology changes are realised by transfers between numerical phases, which are treated differently according to the basic simulation methodologies mentioned above.
In that sense, entrainment processes are characterised by multiple numerical aspects: 1) entrapping of large-scale gas structures, which subsequently disintegrate into smaller ones and 2) direct conversion of continuous towards disperse portions of gas due to processes taking place at sub-grid scales, which are described by dedicated entrainment models, such as the one of Ma et al. (2011). In this work, the individual effects as well as the interplay of the aforementioned processes are assessed and validated in comparison to experimental data of a liquid plunging jet (Chanson et al., 2004). This also considers the balance between the two numerical aspects mentioned above. The goal is to improve the reliability of predictions of gas entrainment with high as well as with low spatial resolution.