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Item type:Publication, Flow-field analysis and performance assessment of rotating detonation engines under different number of discrete inlet nozzles(Elsevier Ltd, 2024-12-01)This study explores in depth rotating detonation engines (RDEs) fueled by premixed stoichiometric hydrogen/air mixtures through two-dimensional numerical simulations including a detailed chemical kinetic mechanism. To model the spatial reactant non-uniformities observed in practical RDE combustors, the referred simulations incorporate different numbers of discrete inlet nozzles. The primary focus here is to analyze the influence of reactant non-uniformities on detonation combustion dynamics in RDEs. By systematically varying the number of reactant injection nozzles (from 15 to 240), while maintaining a constant total injection area, the study delves into how this variation influences the behavior of rotating detonation waves (RDWs) and the associated overall flow field structure. The numerical results obtained here reveal significant effects of the number of inlets employed on both RDE stability (self-sustaining detonation wave) and performance. RDE configurations with a lower number of inlets exhibit a detonation front with chaotic behavior (pressure oscillations) due to an increased amount of unburned gas ahead of the detonation wave. This chaotic behavior can lead to the flame extinguishing or decreasing in intensity, ultimately diminishing the engine's overall performance. Conversely, RDE configurations with a higher number of inlets feature smoother detonation propagations without chaotic transients, leading to more stable and reliable performance metrics. This study uses high-fidelity numerical techniques such as adaptive mesh refinement (AMR) and the PeleC compressible reacting flow solver. This comprehensive approach enables a thorough evaluation of critical RDE characteristics including detonation velocity, fuel mass flow rate, impulse, thrust, and reverse pressure waves under varying reactant injection conditions. The insights derived from the numerical simulations carried out here enhance the understanding of the fundamental processes governing the performance of RDE concepts. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Direct numerical simulations of two-phase fluids interface in 2D rotating drums using a coupled VOF–IBM numerical approach(Begell House Inc., 2024-01-01)Rotating drums play important roles in numerous industrial applications, such as mineral processing. This work is focused on the numerical study of the interface evolution in liquid–liquid and liquid–gas phase rotating drums. A new coupling strategy between volume of fluid (VOF) and immersed boundary method (IBM) approaches is developed. Relevant dimensionless numbers, including Reynolds, Froude, and Bond numbers, alongside viscosity and density ratios, are considered for the flow pattern characterization. Direct numerical simulations are performed in order to explore flow regimes within the rotating drum, addressing a gap in the literature concerning less-explored flow patterns, particularly in the rotating drum containing liquid–liquid phases. The flow pattern families characterizing rotating drums carrying liquid–liquid phases found in this study are (i) gravity stratified, (ii) mixing, (iii) annular, and (iv) rotation stratified flows. Additionally, the characteristic flow pattern families, gravity stratified, (ii) pool, (iii) annular with pool, and (iv) annular flows, are identified in rotating drums carrying liquid–gas phases. The difference in the transitory responses between the rotating drum featuring liquid–liquid and liquid–gas phases is also shown and discussed. The main results highlight significant contributions for understanding the dynamics of rotating drums, particularly concerning the transitional interface development. By identifying new flow patterns and exploring transitional phenomena, this study enriches the understanding of complex fluid behavior within rotating drum configurations. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Computational assessment of soot models in ethylene/air laminar diffusion flames(Taylor and Francis Ltd., 2024-01-01)To improve the accuracy of soot formation and evolution predictions, several physical and chemical models have been developed over the last decades. These models include (i) detailed chemical kinetic mechanisms describing both gas-phase chemistry related to combustion processes and reaction pathways leading to large-sized aromatic molecules, which are needed for modelling soot formation, and (ii) soot models providing a comprehensive description of soot particle dynamics and interactions with gas-phase chemical species. Accordingly, in this work, two detailed soot models, the method of moments (MOM) and the discrete sectional method (DSM), are evaluated in ethylene/air laminar diffusion flames, and their corresponding results are compared with experimental measurements. Furthermore, the NBP and KM2 chemical kinetic mechanisms are assessed and compared with each other by examining key chemical species related to soot formation and evolution. To compute gas mixture’s radiative properties, the weighted sum of grey gases model considering a grey medium is also utilised. Finally, the contributions of the soot precursors known as PAH (polycyclic aromatic hydrocarbon) to soot formation are also analysed. The main results show that the discrepancies in PAH concentrations obtained with different chemical kinetic mechanisms can be significant. In addition, compared to MOM ones, DSM results obtained here show a better agreement with experimental data. Finally, the analysis of PAH shows that those with two (A2) to four (A4) aromatic rings impact the most on soot modelling. Specifically, contributions of A4 were found to be more significant at lower heights above the burner, whereas A2 was found to be more impactful downstream as the flame develops. Maximum contributions of A2 and A4 to the soot inception rate were 66% and 85%, respectively, whereas the maximum summed contribution of PAH with five (A4R5) to seven (A7) aromatic rings accounted for only 13% of the inception rate. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Qualitative and quantitative analyses of particulate flows in rotating drums using a DEM-based approach(Springer Science and Business Media Deutschland GmbH, 2024-10-01)In mineral processing, ore grinding is an energy-intensive process. Tumbling mills used in grinding processes can be accounted for as rotating drums with liners. As part of an effort to evaluate ways of reducing energy consumption in such systems, therefore, particulate flows in rotating drums are studied in this work. More specifically, using a new DEM tool, which is one of the modules of a larger in-house computational package called CFLOWSS, particulate flows in rotating drums are qualitatively and quantitatively analyzed. The results from such analyses are compared with experimental ones and other numerical results obtained using a commercial DEM software. In qualitative terms, the CFLOWSS results show a relatively good agreement with experimental photographs previously taken in a laboratory. In quantitative terms, in turn, the CFLOWSS predictions show a strong correspondence with those ones made by the commercial software. For instance, the relative discrepancies of the boxplots’ medians associated with the number of contacts, power, and forces predicted by both (in-house and commercial) tools present values smaller than 8%. At a 60 RPM drum rotation velocity, indeed, the number of contacts related discrepancies reach values as low as 0.8%. Some of the contributions of this work involve (i) the development of a new DEM tool capable of realistically describing particulate flows in rotating drums, and (ii) the use of statistical treatments to quantitatively analyze DEM results. This last aspect is important because this sort of assessments provides an improved way to analyze the behavior of particulate flows. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, On the application of sliding mode control to indirectly coupled photovoltaic-electrolyzer systems used in the production of clean energy(Elsevier B.V., 2024-08-01)To improve the performance of photovoltaic-electrolyzer (PV-EL) systems, it is key to operate them at the right operating conditions, not only at design point but also at off-design. In addition, when directly coupling a PV system to an EL one, an ideal sizing of the resulting PV-EL coupled system ensuring the best interaction between the PV system and the EL stack is not always possible. Coupling indirectly PV systems to EL ones, through DC/DC converters for instance, results thus advantageous. Accordingly, this work discusses the application of sliding mode control (SMC) to indirectly coupled PV-EL systems, which allows them to operate as efficient as possible. The control scheme employed here includes mathematical models for both the PV system and the EL stack, and for the DC/DC converter and the sliding mode control algorithm utilized. To determine their influence on the obtained results, two different converter topologies are assessed here. Some of the results obtained emphasize that using a DC/DC converter can significantly increase the hydrogen produced by PV-EL systems, especially when it is paired with a control algorithm like SMC. This effort represents one of the first works involving the application of sliding mode control to indirectly coupled PV-EL systems.