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In this study, an incompressible and immiscible two-phase flow solver was employed to assess the accuracy of phase-interface capturing methods in simulating two-phase flows. Three benchmark investigations were conducted involving two dam break flows with deformable free surfaces and the upward motion of a gas bubble through a liquid column. Four phase-interface capturing schemes, namely, MULES, HRIC and CICSAM from the Color Function Volume of Fluid (CF-VoF), and Interface Reconstruction Volume of Fluid (IR-VoF), were utilized. Comparative analysis of the phase interfaces indicated that CICSAM and IsoAdvector consistently provided sharp interfaces across all cases when compared to MULES and HRIC. The mass conservation performance of all schemes excelled in the dam-break case with relatively simple free-surface development and the rising bubble case. An examination of the local pressure distribution over time revealed that methods yielding diffusive interfaces produced inaccurate results. Thus, the importance of employing denser grids or schemes that yield sharper interfaces, such as CICSAM and IsoAdvector, to enhance simulation accuracy was underscored. Overall, the results of this analysis confirm that the IsoAdvector scheme, which provides sharp interfaces, is a reliable option for simulating incompressible immiscible two-phase flows. [ABSTRACT FROM AUTHOR]

Advances in hybrid surfaces have revealed interesting opportunities for multiphase flow control under microgravity, as the surface tension force is dominant in this condition. However, a comprehensive investigation of bubble generation rates and slug flow parameters remains challenging. This research integrates hybrid wettability and modified dynamic contact angle models to address this important knowledge gap. Using the computational capabilities of the IsoAdvector multiphase method, we performed detailed simulations of complex multiphase flow scenarios with the OpenFOAM package. We then validated these simulation results through rigorous comparison with available experimental data, thereby strengthening the accuracy and reliability of our numerical simulations. Our comprehensive research demonstrates the profound effect of altering contact angle distribution patterns on several critical parameters. These results highlight the precise control that can be achieved through the strategic manipulation of these patterns, offering the possibility of adjusting factors such as bubble production rate, slug length, bubble diameter, the relationship of flow residence to bubble movement, bubble movement speed in the channel, and pressure drop. Interestingly, altering these patterns can also induce asymmetric behavior in bubbles under microgravity conditions, a phenomenon that has significant implications for various applications. Such insights are crucial for fields such as heat transfer in energy systems, reaction mechanisms in chemical processes, multiphase flow control in petrochemical industries, fluid dynamics in aerospace engineering, and cooling mechanisms in electronic devices. With the ability to modulate these fundamental parameters, we gain valuable insights into the design and optimization of microchannel systems. Consequently, this research presents a more efficient and innovative approach to multiphase flow control, promising improved operational performance, and efficiency in various engineering applications. [ABSTRACT FROM AUTHOR]

This study examines the reaction zone structure of syngas/NH 3 /CH 4 blends in moderate or intense low oxygen dilution (MILD) conditions to determine the effects of variations in NH 3 and syngas mole fractions upon the stability of the reacting system and NO x emission. A series of axisymmetric turbulent combustion simulations are performed using OpenFOAM and selected reaction mechanisms and, a modified version of the eddy dissipation concept. An increasing amount of syngas is added to the reacting mixtures of NH 3 /CH 4 in MILD conditions. It is observed that a reduction in the NH 3 mole fraction increases the OH radical concentration, which implies a reduction in the ignition delay. Further, for a given NH 3 mole fraction, an increase in the syngas content of the fuel blend along with a reduction in CH 4 leads to a rise in the process maximum temperature near the entrance zone. This reduces the flow temperature gradient, decreases the CH 2 O mass fraction, and boosts the stability of MILD combustion. Additionally, adding syngas to ammonia for MILD combustion decreases the reaction zone weakening, which is a major problem in MILD combustion of ammonia. In particular, blending syngas with NH 3 and reducing the amount of CH 4 in the fuel blend increases flame speed and heat generation. When syngas is added to ammonia MILD combustion, NO x and N x O decrease, and more complete combustion is achieved. • A modified EDC model was used to study the effect of adding syngas to a blend of NH 3 /H 2 /CH 4 for MILD combustion. • Adding syngas to NH 3 -MILD combustion decreased the weakening of the reaction zone. • Adding syngas to a fuel blend of NH 3 and reducing the amount of CH 4 increased the flame speed and heat production. • The addition of syngas to NH 3 for mild combustion reduced NO x and N x O emissions. [ABSTRACT FROM AUTHOR]