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Boundary Conditions and Initial Value Lines for Unsteady Homentropic Flow Calculations

Published online by Cambridge University Press:  07 June 2016

W. A. Woods  and
H. Daneshyar
W. A. Woods
Affiliation:
University of Liverpool
H. Daneshyar
Affiliation:
Cambridge University
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Summary

A detailed discussion on the difference between an initial value line and a line characterised by a boundary condition has been presented. Two types of boundaries are described and illustrated. To examine each boundary, several different calculations have been performed for a straight pipe. The results of the numerical calculations are compared with an analytical solution. It is shown that known pressure and velocity at the pipe ends give the most accurate results. Comparisons are also made between several practical types of calculations which give similar findings. The use of time-dependent boundaries can lead to errors as large as 40 per cent in derived results. It is shown that good accuracy can be restored by converting the boundaries into initial value lines. It is concluded that in general no more than one time-dependent boundary should be used in any calculation. Finally it is demonstrated that errors are not revealed by means of pressure diagrams alone.

Type
Research Article
Information
Aeronautical Quarterly , Volume 21 , Issue 2 , May 1970 , pp. 145 - 162
Copyright
Copyright © Royal Aeronautical Society. 1970

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