Modeling and Predicting Deflagration Phenomena in Hydrogen-Enriched Gas Turbine Exhausts: A CFD Approach

Abstract

Abstract The adoption of hydrogen-enriched fuels in gas turbine power plants is gaining prominence as an effective strategy for decarbonization. However, this transition presents unique challenges, particularly in relation to hydrogen’s wider flammability range compared to natural gas when mixed with air. Under certain operating conditions, this can lead to the undesired formation of flammable mixtures within the gas turbine exhaust channel, which, if ignited, can result in structural damage due to pressure increases caused by the deflagration process. An effective and robust way of assessing the related safety risk is to rely on high-fidelity Computational Fluid Dynamics (CFD) models, capable of accurately predicting the overpressure generated by the ignition of flammable mixtures. In this study, a CFD model has been developed to perform three-dimensional and unsteady simulations of the deflagration of hydrogen-air mixtures within large partially confined volumes, representative of an industrial gas turbine exhaust. A high-fidelity Large Eddy Simulation (LES) approach coupled with the Renormalization Group Theory (RNG) subgrid-scale model was employed for turbulence modelling, while the Flamelet Generated Manifold (FGM) tabulated chemistry approach with the Turbulent Flame Speed Closure (TFSC) was adopted as the combustion model. Computational results have then been compared to experimental data from the literature to validate the presented model in terms of numerical domain discretization, turbulence modelling, and combustion modelling. The analysis is aimed at replicating the main overpressure peaks as measured by the British Gas Midlands Research Station. While exhibiting a satisfactory alignment with the experimental pressure distribution in the test case, the proposed setup was able to capture the primary dynamics of the deflagration process, demonstrating its readiness for application to real gas turbine exhaust geometries. The setup has been then used to simulate the deflagration process of a hydrogen-air mixture at the exhaust of an industrial gas turbine manufactured by Baker Hughes. A discussion on this latter case has been reported as well in this paper.