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A comprehensive investigation of acoustic power level in a moderate or intense low oxygen dilution in a jet-in-hot-coflow under various working conditions.

Although the impact of impinging droplets on solid substrates has been widely studied, any possible non-trivial interaction between the substrate wettability and applied electric field toward altering the underlying dynamical characteristics remains unexplored. In this study, the interaction between electric field and hydrodynamic transport, toward influencing the dynamic behavior of a water droplet, dispersed in an immiscible fluid, on solid substrates has been numerically investigated. Finite element simulations were performed with a conservative level-set method to track the liquid-liquid interface. The numerical method is first validated with the available experimental data. After ensuring the accuracy of the simulation method, the effects of variations in impact velocity, electric field strength, electric permittivity of the surrounding liquid, and substrate wettability have been studied to clarify the underlying physics of this problem. These results may turn out to be of profound importance toward understanding the functionalities of various practical applications and manipulating the droplet dynamics through surface wettability-electric field interaction over the relevant spatiotemporal scales.

This paper examines the effects of swirl hot co-flow on the combustion behavior of a moderate or intense low oxygen dilution (MILD) burner fueled by a mixture of methane and hydrogen. Toward this goal, the realizable k-ɛ turbulence model, GRI. 2.11 reaction mechanism, and the discrete ordinates radiation model are incorporated into a computational modeling of the reactive flow. The numerical results are, first, favorably compared against the existing experimental data. Subsequently, a number of swirl co-flows are implemented, and structures of the resultant reactive flows are investigated systematically. The outcomes indicate that increasing the swirl velocity leads to the reduction of ignition delay and significantly enhances the reaction completion. The analysis of the spatial distribution of hydroxyl and formyl (OH and HCO) radicals reveals that swirling MILD combustion radially extends the reaction zone in comparison with the conventional MILD combustion. Yet, it reduces the length of the reactive region and allows for the occurrence of heat release in a shorter axial distance from the outlet fuel nozzle. Further, the addition of swirl reduces the production of carbon monoxide through its influences upon flow temperature and generation of formyl radical. However, it is found that swirling hot co-flow intensifies NOx emissions by strengthening of prompt and thermal mechanisms of NOx production. Reducing the temperature of the recycled flue gas is deemed to be an effective way of resolving this issue.

In this paper, the Pseudo shock structure in a convergent-long divergent duct is investigated using large eddy simulation on the basis of Smagorinsky-Lilly, Wall-Adapting Local Eddy-Viscosity and Algebraic Wall-Modeled LES subgrid models. The first objective of the study is to apply different subgrid models to predict the structure of Lambda form shocks system, while the ultimate aim is to obtain further control of the shock behavior. To achieve these goals, the dynamic grid adaption and hybrid initialization techniques are applied under the 3D investigation to reduce numerical errors and computational costs. The results are compared to the existing experimental data and it is found that the WMLES subgrid model results in more accurate predictions when compared to the other subgrid models. Subsequently, the influences of the divergent section length with the constant ratio of the outlet to throat area and, the effects of discontinuity of the wall temperature on the flow physics are investigated. The results indicate that the structure of compressible flow in the duct is affected by varying these parameters. This is then further discussed to provide a deeper physical understanding of the mechanism of Pseudo shock motion.

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