The Impact of the Off-Design Conditions on the Entropy Wave Interaction With a High-Pressure Turbine Stage

The study of component interactions in aeronautical engines is a key aspect to improve the aerodynamic, aeromechanical, and thermal performance and to reduce greenhouse gas and noise emissions. In this context, combustor systems (working with lean and premixed flames) generate pressure, velocity, and temperature fluctuations that interact with the turbine module producing combustor instability, performance degradation, and noise generation. A correct understanding of this interaction is thus required by the designers, especially with a view to introducing sustainable aviation fuel to achieve zero-emission aviation. This paper tackles this topic from a numerical and experimental point of view, focusing on off-design turbine conditions possibly encountered during an aero-engine mission. In detail, the effect of different stage loadings (obtained by keeping the stage pressure ratio and modifying the rotational speed) on engine-representative entropy waves evolving through the turbine stage is investigated. The combination of numerical and experimental results, that show a good agreement in terms of disturbance evolution within the stage, allows a deeper understanding of the flow field features that impact the stage aerodynamics and modify the secondary flow structures and the entropy wave transport, diffusion, and decay through the rotor. Moreover, the most loaded operating condition reveals the appearance of a rotating instability at the rotor tip that also interacts with the injected disturbance. Finally, the numerical results (coming from full annulus URANS computation with incoming disturbances) are further post-processed to extract indirect noise emissions at the different load conditions and to assess the additional loading on the rotor blade caused by the presence of the disturbance.