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research-article

Accounting for Uncontrolled Variations in Low-Speed Turbine Experiments

[+] Author and Article Information
Kathryn Evans

Whittle Laboratory, University of Cambridge, 1 JJ Thomson Avenue, Cambridge CB3 0DY, UK
kathryn.evans@cantab.net

John P. Longley

Whittle Laboratory, University of Cambridge, 1 JJ Thomson Avenue, Cambridge CB3 0DY, UK
jpl@eng.cam.ac.uk

1Corresponding author.

ASME doi:10.1115/1.4036342 History: Received September 01, 2016; Revised March 09, 2017

Abstract

It is common to assume that the performance of low-speed turbines depend only on the flow coefficient and Reynolds number. However, when the turbine has an atmospheric inlet and uses unconditioned air, variations in ambient pressure, temperature and humidity are introduced. Whilst it is still possible to maintain the required values for the flow coefficient and Reynolds number, the ambient variations affect additional non-dimensional quantities which are related to the blade speed and gas properties. Generally, these additional non-dimensional quantities are uncontrolled and affect the turbine performance. In addition, thermal effects, which are exacerbated by the use of plastic blades, can cause changes in the blade row seal clearance and these also affect the performance. Therefore to obtain measurements with greater accuracy and repeatability, the changes in the uncontrolled non-dimensional quantities must be accounted. This paper contains four parts. Firstly, it is described how suitable data acquisition parameters can be determined to eliminate short time scale facility unsteadiness within the measurements. Secondly, by the analysis of models, the most appropriate forms for the additional non-dimensional quantities are obtained. Since the variations in the uncontrolled non-dimensional quantities affect repeatability the size of the effect on the turbine performance is quantified. Thirdly, a best-fit accounting methodology is described which reduces the effects of the uncontrolled non-dimensional quantities on turbine performance provided sufficient directly related measurements are available. Finally, the observations are generalised to high-speed turbomachines.

Copyright (c) 2017 by ASME
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