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The Polytropic Expansion of Air Through a Convergent Nozzle at Infinite Pressure Ratio—An Interesting Anomaly

Published online by Cambridge University Press:  07 June 2016

H. Pearson
H. Pearson*
Affiliation:
Rolls-Royce Limited
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Summary

Previous papers have examined the implications of an assumed polytropic expansion law on the performance of nozzles. In this paper a peculiar anomaly is examined when the convergent nozzle is exhausting into a vacuum. It is shown that, on the strict assumptions of a polytropic expansion law, and the assumption that the flow will maximise for a given throat area, the thrust per pound of air increases progressively with falling polytropic efficiency, becoming infinite when the polytropic efficiency is zero. The author suggests that this anomaly is either concerned with the assumption that the flow will maximise or means that polytropic expansion efficiencies below a certain limit are theoretically impossible, but he believes that there may be some other explanation.

Type
Research Article
Information
Aeronautical Quarterly , Volume 13 , Issue 4 , November 1962 , pp. 301 - 307
Copyright
Copyright © Royal Aeronautical Society. 1962

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References

1. Moyes, S. J. The Critical Flow Conditions of a Gas in a Convergent Passage and the Influence of Frictional Losses. R. & M. 2045, 1942.Google Scholar
2. Naylor, V. D. The Critical Flow of a Gas Through a Convergent Nozzle. Aircraft Engineering, p. 160, June 1951. Flow of a Compressible Gas with Friction. Aircraft Engineering, p. 308, October 1951. An Experiment on Nozzle Flow. Aircraft Engineering, p. 344, November 1952.Google Scholar
3. There is also a series of letters resulting from the first of V. D. Naylor’s papers.Google Scholar
Spalding, D. B., Naylor, V. D. and Stephenson, J. M. Aircraft Engineering, p. 238, August 1951.Google Scholar
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Naylor, V. D. Aircraft Engineering, p. 83, March 1952.Google Scholar
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