Experimental Investigation and Simulation of a Boeing 747 Auxiliary Power Unit

Abstract

<jats:title>Abstract</jats:title> <jats:p>Auxiliary Power Units (APUs) are a major driver of maintenance on civil aircraft. However, experimental data and performance simulations are rarely seen in public domain literature. While there is recourse to aircraft engine experience, this does not address the loading and the failure modes of an APU. The aim of this work is to significantly add to the literature, by experimentally investigating a Boeing 747 APU, collecting data under various power settings and ambient conditions, and using this data to calibrate a simple simulation model. This simulation model will subsequently be used to explore failure modes in the APU and hence what sensors may be needed for health monitoring purposes in future work. In this paper, a Boeing 747 APU rig development process and the adopted testing strategy are presented. The rig is validated through a process that includes uncertainty analysis, repeatability tests, consistency tests and comparison of the collected data with the calibrated simulation model. The results from the rig's validation indicate that the data collected from the APU is independent of its running time or the order of loading cycles imposed on it, i.e. the results are path independent. The rotational speed shows a slightly increasing trend when the extracted power rises, and this affects the APU thermodynamic characteristics. This work has resulted in a calibrated simulation model that will be further used in examining fault mode scenarios, as injecting these directly into the rig is seen as high risk.</jats:p>

Development of a Far-Field Noise Estimation Model for an Aircraft Auxiliary Power Unit

“…T-MATS allows the development of a customized gas turbine using modular turbomachinery components, which can be analyzed in detail by integrating the model with the softwareprovided iterative solvers. The research community has frequently used T-MATS for simulating the performance of gas turbines ( [1], [23], and [24] are some of the examples), but it has not been adopted for noise modelling purposes.…”

“…The aircraft is a highly complex and integrated system. Amongst, others, one of its major systems, the Auxiliary Power Unit (APU), has been reported as a key driver of unscheduled maintenance and therefore demands a robust maintenance strategy [1]. The heart of maintenance and troubleshooting is a fault diagnostic scheme that comprises a sensor-set and a fault diagnostic algorithm.…”

“…Generally, a diagnostic capability is embedded into the system during the design phase depending on the technologies (hardware, sensors, processing techniques) available at that time. Performance-based monitoring (also called gas-path analysis) is an example of the prevalent approach for a gas turbine's health monitoring or fault detection [1][2][3][4][5][6][7]. However, these methods require the installation of thermodynamic sensors which could be intrusive and may not be feasible if they were not considered during the product's design phase.…”

“…Generally, a test rig is developed to gather information about thermodynamic parameters, acoustics, or exhaust emissions. Several test rigs [1]- [4] have been developed to understand the thermodynamic aspects of APUs. In other forms of experimental data collection, APUs are placed inside an anechoic chamber and their exhaust noise is studied with far-field microphones [5]- [7].…”

Aircraft system-level diagnosis with emphasis on maintenance decisions

“…The APU is a system installed in all commercial aircraft and its purpose is to provide bleed air and electric power to other aircraft systems. Skliros et al 6 describe the principle of operation of a Boeing 747 APU and discuss its performance characteristics under various operating conditions. The APU belongs to the broader category of Gas Turbine (GT) engines, for which a large variety of diagnostic techniques have been developed.…”