Waves, bubbles, and wake structures in liquid-gas flow past a cylinder

The interaction of free surface flow with solid bodies is ubiquitous in offshore structures. Motivated by this, in our numerical study, we consider a canonical setup involving a stationary circular cylinder in liquid-gas flow. The cylinder is immersed in the flowing liquid but kept close to the liquid-gas interface. In the unperturbed state, the liquid-gas interface spanning the horizontal direction is flat, and the flow profile within the liquid is uniform, which develops an interfacial boundary layer in the gas phase. The interplay between the liquid-gas interface and flow perturbations originating from the cylinder leads to three distinct regimes of interface dynamics: interfacial waves driven by Strouhal vortices, entrainment of multi-scale gas bubbles, and the reduced deformation state. These regimes exhibit markedly different wake structures, and the transition across these regimes is regulated by the Bond number and the submergence depth of the cylinder while keeping the Reynolds and Weber numbers fixed. We pay particular attention to bubble-size spectra and breakup mechanisms in the gas entrainment regime and assess the role of Reynolds and Weber numbers. Lastly, we show that the hydrodynamic lift force acting on the cylinder can be tuned using the deformability of the nearby liquid-gas interface.