Effects of turbine matching characteristics on aero-engine surge boundary through a rapid prediction model

Aerodynamic instability in an aero engine can severely degrade its performance and damage its structural integrity. The turbine matching condition changes significantly across the engine’s operating range and strongly affects the throttling characteristics. However, its resulting effect on the stability of aero engines is not yet fully understood. To investigate this effect, this study introduces a reduced-order dynamic model for engine instability analysis. It integrates low-dimensional models of core engine components, such as the compressor, combustor, turbine, and considers the dynamic effects of flow passage lengths and volumes. Validation against real fuel-spiking surge tests shows that the relative errors in surge predictions are less than 4% across the medium to high speed range. The research reveals a non-monotonic effect of turbine matching on the engine instability. As the turbine shifts from a choked to an unchoked condition, the stability boundary on the compressor map shifts toward a lower flow rate (enhancing stability) before shifting back toward a higher flow rate (worsening stability). Notably, the downstream system’s B parameter, a dimensionless criterion characterizing the system’s dynamic stability, determined by the equivalent volume and passage length exhibits a significant coupling effect with turbine matching characteristics. A decrease in the B parameter, especially below a critical value, amplifies this impact, causing a maximum change in the boundary flow rate of up to 2.7%. This rapid prediction model provides an effective tool for stability assessment and for optimizing engine stability during the preliminary engine design stages.