The impact of heat transfer effects on civil aircraft engine transient performance

Abstract

During gas turbine transient manoeuvre, heat transfer occurs between the fluid and metal. This results in various heat transfer effects, including heat soakage, tip clearance, and change in component performance map. These will cause heat loss and change in component flow characteristic and efficiency, which further affect gas turbine transient performance. In this work, a comprehensive heat transfer model including heat soakage, tip clearance and compressor map modification has been developed. The proposed heat soakage model improves the current state-of-the-art model by establishing a comprehensive thermal network with the consideration of the combustor temperature distribution and cooling technologies including film cooling, internal cooling, and thermal barrier coatings. Additionally, the proposed novel compressor map modification model can derive numerical correlations for compressor maps based on movement of compressor speed line and map scaling, enabling the modification of adiabatic maps to non-adiabatic maps during transient simulations. It improves the current compressor map modification models by ensuring both flexibility and accuracy. The developed heat transfer model has been integrated into Cranfield gas turbine simulation platform Turbomatch, enhancing the realism of transient simulations. The accuracy of the proposed model has been validated against data from public sources, simulation platforms, and experimental results. A sensitivity analysis has also been conducted to assess the impact of various assumptions on heat flow rate estimation. The impact of heat transfer to overall engine’s performance has been demonstrated by simulating transient operation of a turbojet and two turbofan engines to demonstrate the effects of heat transfer on gas turbine transient performance. Comparing with the conventional heat soakage method, the application of the improved models can capture a delay on engine’s response beyond the one simulated by the existing methods. This is a result of considering the combustor temperature distribution and cooling technologies, not included in the conventional heat soakage models. For the impact of heat transfer effect on compressor characteristic and performance, a 4% reduction in compressor surge margin is observed during a hot reslam transient manoeuvre, as a result of movement in compressor speed line due to heat transfer effect.