A Test Bed for Small Aero Gas Turbines for Education and for University: Industry Collaboration

Abstract

Engine testing is a necessary but nonetheless expensive and time consuming process. Most of the facilities used to test an engine at sea level static conditions are enclosed test beds. In these facilities the existence of secondary mass flow within the test chamber and around the engine gives rise to various drag components that affect the thrust measurements. For this reason, the net thrust measured in an indoor test bed is lower than the true gross thrust delivered by the engine and measured during outdoor tests. Thrust correction factors, therefore, need to be calculated and applied. For the past five years Cranfield University has been involved in a research study evaluating the performance of gas turbines in test beds, and this work continues. Recently, Cranfield purchased a small gas turbine and invested in the design and construction of a small test bed facility that provides experimental data for the support of the analytical computational fluid dynamics (CFD) analysis. The purpose of this micro-turbojet and test bed facility is to mimic large scale facilities and provide appropriate experimental data for calculating thrust correction factors. The data are also used together with three dimensional CFD models to provide a better understanding of the aerodynamic and engine performance issues involved. Tests have been completed successfully and the facility is capable of detecting the small thrust differences between indoor and outdoor test. Thrust correction factors have been derived through a back to back process. This is an excellent result showing that the equipment is performing as designed. In addition to providing useful results and conclusions in support of ongoing research the facility is also used for postgraduate projects focusing on the performance of small engines in test beds. Analytical design tolls such as commercial CFD and in house engine performance programs are used to predict engine performance and parameters. The results are then validated against the test data. This paper describes the present state of technical progress, which is under development. Its other purpose is to describe the educational value of the analytical and experimental techniques, the objective of which is to mimic the overall engine development process.