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The Measurement of High Speed Air Velocity and Temperature using Sound Wave Photography

Published online by Cambridge University Press:  07 June 2016

D. E. Elliott
D. E. Elliott*
Affiliation:
Liverpool University*
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Summary

A transient sound wave is generated by discharging a spark in an air stream, the velocity and temperature of which are required. After a time interval of about 25 microseconds a shadowgraph photograph of the sound wave is taken; a second photograph is obtained after a further known time interval of the same order. The two exposures, both on the same negative, show the propagation of the sound wave in the air stream and from this the Mach number, the true velocity, the local velocity of sound, and hence the temperature, can be calculated.

Using this method, measurements of Mach numbers of the order of 0·5 gave values between 98 per cent, and 100 per cent, of those calculated from pressure measurements. Typical examples of the sound wave photographs are shown. With further development along the lines indicated in the paper greater accuracy should be possible. The local speed of sound was measured to an estimated accuracy of ±1·5 per cent.

Since only a very short time interval is needed to obtain the photographs, the method appears promising for investigating explosions of brief duration, or dealing with flows of pulsating character.

Type
Research Article
Information
Aeronautical Quarterly , Volume 6 , Issue 3 , August 1955 , pp. 181 - 195
Copyright
Copyright © Royal Aeronautical Society. 1955

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References

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