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Description of a Water Tunnel and Apparatus for the Investigation of Flow Problems

Published online by Cambridge University Press:  28 July 2016

A. Fage  and
J. H. Preston
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Abstract

The water tunnel, closed-return type, described in the paper is especially suitable for the observation of flow near the surface of a long streamline body of revolution at Reynolds numbers up to 1.3 × 106. The observation chamber is 32 ins. long and it has a circular cross-section of diameter 7 ins. The stream in the observation chamber although slightly disturbed at the higher speeds of flow is substantially free from turbulence (except near the wall) at all speeds and throughout its entire length.

The tunnel is equipped with two instruments designed for flow observation. The first instrument, named fluid-motion microscope, allows the movements of small particles in a bright beam of light to be observed and measured. This instrument is suitable for the study of details of flow too small to be seen with the unaided eye, but which are revealed under a microscope at a medium magnification. The second instrument, the fluid-motion microscope with an interrupter, allows the speed of a particle to be determined from a measurement of the length of its track recorded for a known time of exposure on a photographic plate. This instrument can be used to measure the velocity distribution in a boundary layer to a distance of about four thousandths of an inch from the surface.

Type
Research Article
Information
The Aeronautical Journal , Volume 45 , Issue 364 , April 1941 , pp. 124 - 140
Copyright
Copyright © Royal Aeronautical Society 1941

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References

Note on page 124* The water tunnel and its apparatus were designed and constructed in the Aerodynamics Department of The National Physical Laboratory, and descriptions are published on the recommendation of the Aeronautical Research Committee and by permission of the Director of the Laboratory. An account of work made on the tunnel, on transition from laminar to turbulent flow in the boundary layer of a streamline body, will shortly be published in Proceedings of The Royal Society, Vol. 178, A.

Note on page 128 * Fage, and Townend, . Proc. Roy. Soc., A, Vol. 135, 1932, pp. 656–684 CrossRefGoogle Scholar. Fage, . Phil. Mag., Vol. 21, 1936, pp. 80–105 CrossRefGoogle Scholar.

Note on page 132 * This difficulty only arises when the turbulence is small: e.g., 0.1 per cent, steps in speed are needed to measure a maximum turbulent velocity component which is 1 per cent, of the mean velocity to an accuracy of 10 per cent.

Note on page 133 * Fage (loc. cit.).

Note on page 138 * The size of the particle is immaterial when measurements are made from the beginning of one streak to the beginning of the next streak.

Note on page 139 * It should be noted that the radius r is not constant.