A Numerical Investigation of Aerodynamically Trapped Vortex Combustor for Premixed Hydrogen Combustion in Gas Turbines Using Detailed Chemistry

Abstract

Hydrogen is a clean and carbon-free fuel and is considered a key element for the energy transition. Renewable power generation by solar and wind is increasing, requiring flexible operation to balance the load on the energy grid with the ability to rapidly adjust the output. Gas turbines with a combustion system for hydrogen operation offers a low carbon solution to support the stability of the energy grid. This provides a solution capturing the needs for energy storage, in the form of hydrogen, and flexible power generation. High flame temperatures in the primary zone facilitates the production of NOx which can be reduced by using premixed combustors. But this introduces the risk of flame flashback. Several combustor concepts have been proposed and studied in the past few years to tackle the problem of flame flashback in premixed high hydrogen fuel combustors. This study looks at one of the concepts which uses Aerodynamically Trapped Vortex to stabilize the flame and studies the flow and flame behavior in the combustor. Numerical simulations for the analysis were performed with commercial Computational Fluid Dynamics (CFD) simulation package AVL FIRE™. The flow field characterization was focused on the investigation of the influence of the inlet velocity and inlet turbulence intensity (u′) on the mean velocity, wall velocity gradient and turbulence intensity in the combustor. To study the flame stabilization mechanism, reactive simulations were performed at two fuel equivalence ratios. The combustion regime of the flame, wall velocity gradient and temperature distribution in the combustor were quantified from the simulation results. A validation study was performed prior to the analysis of the ATV combustor to validate both the turbulence and the reactive models for premixed hydrogen combustion. The models were validated against the experiments performed in a dump stabilized cylindrical combustor at Combustion Research Laboratory, Paul Scherrer Institute (PSI), Switzerland. The k-ε and k-ζ-f turbulence models were selected for modelling the turbulence. Simulations of non-reacting flow with k-ε model resulted in a more accurate prediction of the flow field, turbulence levels and recirculation zone than the k-ζ-f model. Combustion is modelled using the FIRE™ detailed chemistry solver with the k-ε turbulence model to resolve turbulence. No additional turbulence-chemistry interaction model is used in the current research. To reduce chemistry computational time, the multi-zone method is employed. A detailed chemistry approach with sufficient mesh resolution for modelling the reaction in 100% premixed hydrogen combustion predicted the flame behavior with acceptable accuracy. The flow analysis in the Aerodynamically Trapped Vortex (ATV) combustor revealed that the inlet velocity or inlet turbulence had no significant effect on the relative turbulence properties in the flame stabilization zone. The proposed design for the Aerodynamically Trapped Vortex (ATV) combustor was able to stabilize a 100% premixed hydrogen flames without flashback for the simulated conditions.