Detonation physics of H2-air blend in closed bended ducts: A comprehensive numerical analysis

In this research study, a comprehensive investigation was undertaken to delineate the deflagration to detonation transition (DDT) of a hydrogen–oxygen (H2–O2) mixture within the confined environment of a closed duct featuring multiple structural variations, namely smooth, single bend, double bend, and triple bend configurations. The computational modeling and simulation tool, OpenFOAM, an open-source Computational Fluid Dynamics (CFD) package, was used for this purpose, enabling a robust and detailed exploration of the topic. The primary focus of the study was to scrutinize the implications of hydrogen distribution within the mixture, a critical factor in the transition process. To facilitate this, we utilized a vertical concentration gradient of hydrogen, a tactic aimed at generating a rich variety of conditions and subsequently providing a comprehensive understanding of the processes involved. To enhance the robustness of our methodology, the investigation employed both pressure and density-based algorithms, thereby broadening the analytical perspective and improving the accuracy of results. In order to establish a connection between the velocity and pressure fields — a crucial aspect to accurately simulate fluid dynamics — the Pressure-Implicit with Splitting of Operators (PISO) algorithm was applied. This served as a key component of the methodology, bridging the gap between the two essential parameters and allowing for an integrative analysis. To further extend the scope and increase the preciseness of the simulation, various reaction mechanisms, including the Battin-Leclerc, Baulch, Glassman, Lutz, Maas, Miller, Tan, Wang, Westbrook and Ó-Conaire mechanisms, were applied. The results of the simulations showcased the superior predictive capabilities of the Ó-Conaire mechanism, with an accuracy of 98% in representing the transition from DDT, as evidenced by a comparison with existing experimental data. Following this validation of the numerical results through the Ó-Conaire mechanism, the investigation delved deeper into the structural composition of the DDT process in relation to various closed duct geometries. It was demonstrated that alterations in duct geometry significantly impacted the structural nature of detonation. Thus, the study broadened our understanding of how spatial constraints and configurations of a system can dramatically influence the outcomes of highly reactive processes such as the DDT.