University of Florence
Lean burn technology is probably one of the most promising solutions for the next generation of low-emission aeroengine combustors. NOx emissions are limited by controlling the maximum temperature through lean fuel-air mixtures in the burning region. This demands a careful design of the injection system, where the control of fuel breakup and mixing is of paramount importance. Flame stabilization with large swirling flows generates a strong interaction with the liner cooling system, whose thermal design is made even more challenging by the shortage of air available for cooling. In addition, the compactness of the combustion chamber and the absence of dilution holes generate harsh aerothermal conditions at the combustor exit. The uncertainty associated with the presence of highly nonuniform temperature patterns and high turbulence intensity makes it necessary to include wide safety margins in the design, with detrimental effects on the engine performance.
Researchers at HTC Group used ANSYS Fluent to perform scale-resolving simulations to overcome the limitations of standard RANS models in predicting turbulent mixing. Through high-fidelity simulations, it was possible to describe thoroughly the fuel breakup process, thus providing accurate boundary conditions for reactive simulations of spray flames. This approach successfully reproduced the flow physics of the swirling flow and its interaction with the combustor liners, improving the prediction of the heat loads and ultimately the metal temperature. Reproducing the formation of hot streaks and their propagation toward the turbine highlighted the actual performance of the nozzle cooling system under realistic conditions, allowing a lower coolant consumption. Overall, the intrinsic multiphysics nature of the combustor-turbine module proved the capabilities of ANSYS software to contribute pervasively to the design of future low-emission aeroengines.