Turbulence and Pseudo-turbulence in Buoyancy-Driven Bubbly Flows: An Interface-Resolved DNS Approach*

Bubbly flows affect mixing and mass transfer in chemical reactors, nuclear reactor cores, and wastewater treatment plants. By employing interface-resolved direct numerical simulations with a conservative diffusive interface method, this study explores bubble-induced turbulence, especially near-wall turbulence, and energy budgets in a flow with 2.7% volume fraction deformable air bubbles dispersed in water, and with density and viscosity ratios of 0.001 and 0.01, respectively. Our investigation focuses on how key dimensionless parameters such as Galilei number (ranging from 390 to 1100) and Eötvös number (ranging from 0.85 to 8.5) affect flow dynamics and energy budgets. Our findings reveal distinct bubble distribution patterns influenced by the Eötvös number. With lower bubble deformability (Eo = 0.85), bubbles predominantly accumulate near walls, while fewer bubbles are found in the center, exhibiting a more uniform central distribution. In contrast, higher deformability (Eo = 8.5) enhances breakup dynamics and causes bubbles to concentrate in the center, with fewer near the walls. This redistribution of bubbles significantly impacts the upward flow pattern, increasing the flow rate and fluctuations in the channel center and decreasing them near the walls. Furthermore, higher Galilei numbers lead to increased mean and fluctuation velocity statistics and elevated vorticity levels within the viscous sublayer, which in turn enhances the dissipation rate, particularly near the walls.