Numerical investigation of a first-stage stator turbine blade subjected to NH₃–H₂/air combustion flue gases

Blending ammonia with hydrogen has the potential to replace conventional hydrocarbon fuels of jet engines and gas turbines to reduce carbon emissions. Previous research on the 70% NH₃–30% H₂ (vol%) fuel blend characterized its cycle efficiency and emissions, however, the thermal and aerodynamic effects of the NH₃–H₂/air combustion flue gases on the turbine blades were not identified. Therefore, the novelty of the analysis presented herein appears in characterizing such effects of the NH₃–H₂/air combustion flue gases on a generic turbine blade model using CFD simulation for lean (Φ = 0.75), stoichiometric (Φ = 1.00), and rich (Φ = 1.25) equivalence ratios, which are compared to a CH₄/air combustion flue at Φ = 0.75, 1.00 and 1.25, respectively. Based on the obtained results, a cooling channel's ability to reduce the blade's temperature was negligible based on the temperature difference between the leading edge of the turbine blade and the temperature of the combustion flue gas at the inlet. As the combustion equivalence ratio was increased from 0.75 to 1.25, a second shockwave forms at the leading-edge surface, projecting across the blade's lower edge. The formation of the second shockwave was found to be increasingly significant for the NH₃–H₂/air mixture on the downstream flow when compared to a CH₄/air flue gas. Furthermore, increasing the NH₃–H₂/air equivalence ratio improved the blade's ability to increase the average overall outlet Mach number compared to the inlet flow. Flow separation near the trailing edge remained relatively unaffected with increasing equivalence ratio. However, separation near the leading edge at the blade's lower edge becomes more significant for the NH₃–H₂/air combustion flue gases compared to CH₄/air combustion, causing a large circulation zone under the blade's lower surface due to the higher kinematic viscosity for the NH₃–H₂ fuel to the CH₄ fuel (i.e., 2.06 ×10⁻⁵cm²/s and 1.75 ×10⁻⁵ m²/s, respectively). The circulation induces a higher viscous force and fluid inertia in the boundary layer, causing higher levels of separation. Turbulence intensity was also found to be significantly increased for the NH₃–H₂/air flow to that of the CH₄/air combustion flue gases with increasing equivalence ratio.