Acoustic Thrust Estimation on Turbofan Engines

Abstract

An acoustic time of flight sensor is operated across a turbofan exhaust plume and is calibrated to provide nozzle thrust in a ground-test cell. Such a sensor could potentially be used to monitor any degradation of engine performance in an on-wing application. Validation of the technique was performed on an AE3007-A1E turbofan engine. Using a pneumatic horn and a set of microphones, the acoustic time of flight across the exhaust plume was estimated. A correlation-based approach was then used to relate the acoustic time of flight to the thrust produced by the engine. The thrust estimates resulting from this single-receiver approach matched load cell data within a root-mean-square (RMS) error of 1.1% full scale. The same approach was also used to estimate the thrust of a TFE731-2B engine. In that case, the estimated thrust matched load cell data to within an RMS error of 1.5% full scale. The technique is shown to significantly improve on a previous technique that produced errors of 5% RMS full scale or greater. Possible explanations for the comparative inaccuracy of the previous technique are analyzed.