Development and validation of a transient gas turbine simulation tool for shaft-failure modelling

Abstract

New civil engines must demonstrate, either by testing or analysis, that a shaft failure event will not result in hazardous engine effects. Without an accurate method of predicting levels of turbine overspeed, disk design tends to be pessimistic which leads to a weight penalty. This paper presents an alternative approach based on a highly integrated, multi-disciplinary, dynamic whole-engine simulation tool capable of predicting a gas turbine engine’s behaviour following the failure of a shaft. It describes the methodology and validation of a 1D through-flow compressor model capable of post-stall simulation, coupled with a transient combustor model and a quasi-steady turbine solver for overspeed modelling. The individual components are integrated aerodynamically and mechanically to produce a transient whole-engine model which is resolved at timesteps ranging from 1 to 100 μs. Control and aerodynamic effects impacting turbine overspeed predictions include changes in handling bleeds, fuel supply, turbine capacity reduction due to overspeed, frictional torque and variable geometry malschedule. The modelling of a gas turbine engine’s response following a surge event is required for overspeed modelling which is achieved using compressor characteristics defined from normal operation to reverse flow. The whole engine simulation tool is validated against a 3-spool experimental gas turbine engine which experienced a shaft failure event on a test stand. The simulation model correctly predicted the turbine’s terminal speed within a 4% error margin and blowdown rate following a surge event until recovery.