Annulus wall temperatures and heat transfer coefficients in aeroengine compressors deduced from engine measurements

Abstract

Surface-mounted thermocouples were located on the annulus walls of every stator stage in both core compressors of a large civil aeroengine. The relationships of the steady state wall temperatures to the compressor inlet and exit air temperatures are shown, as is their variation with engine rotational speed. The transient response of the thermocouples to fast engine throttle manoeuvres was measured, for acceleration to full power, deceleration to idle and for both acceleration and deceleration to two intermediate power levels. Heat transfer coefficients are deduced from the matching of a thermal finite element model to the measured transients and are expressed as factors with respect to the standard free-disc formula. The variations in the factors through the compressor and through the speed range are shown. The advantages and disadvantages of using an alternative standard formula, based on duct flow, are discussed. Finally, the importance of understanding the transient local air temperature response arriving at a compressor stage due to upstream slugging is shown.