Reduced Order Transient Disc Temperature Models for Online Health Monitoring

Non-uniform temperature distributions in aircraft turbine and compressor discs result in high thermal stresses, particularly during engine transients. This has an important role in limiting disc life and subsequently engine time on wing between overhauls. Typically, and in the absence of specific engine real-time information, disc life is computed and declared at the design stage, for the whole fleet assuming worst case scenarios and flight profiles. This approach potentially leads to conservativeness in disc life prediction for the majority of the engines in the fleet. The purpose of this paper is to present a novel methodology to estimate the transient temperature distribution of such components in real-time, with the ultimate aim of using such information to improve knowledge about disc life consumed on an engine by engine basis. The paper describes a reduced order dynamic model that estimates the disc temperature distribution in real-time using only measured parameters such as spool speed, atmospheric pressure, and compressor exit temperatures. The model presented is a grey box model consisting of dynamic Linear Parameter Varying transfer functions that relate measured air temperatures to the relevant air temperatures in the disc cavities. Heat transfer from air to disc is modelled using rotor-stator aerothermal theory matched to validated computational fluid dynamic analyses. Lumped capacitance models and simplified explicit conduction models are used to simulate the disc temperature distribution. It is shown that this approach gives a scientifically accurate estimate of the temperature distribution both radially and axially, whilst being computationally efficient enough for real-time Engine Health Management implementation.