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• January 20, 2017 Create Date
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National Advisory Committee for Aeronautics, Technical Notes - Development of Turbulence Measuring Equipment

Hotwwire turbulence-measuring equipment has been developed to meet
the more-stringent requirements involved in the measurement of fluctua—
k tions in flow parameters at supersonic velocities._ The higher mean speed
necessitates the resolution of higher frequency components than at low
speed, and the rriatively low turbulence level present at supersonic
speed makes necessary an improved noise level for the equipment. The
equipment covers the frequency range from 2 to about 70,000 cycles per
second. Constant-current operation is employed. Cozpensation for hot-
wire lag is adjusted manually using square-wave testing to indicate
proper setting. These and other features make the equipment adaptable
to all-purpose turbulence work with improved utility and accuracy over
that of older types of equipment. Sample measurements are given to
demonstrate the performance.

The hot—wire technique at low subsonic speeds has become a standard
tool of turbulence research. When high-speed and supersénic wind tunnels
appeared, the interest was focused more on the effects of compressibility
than viscosity. ‘This led to the accumulation of a wealth of data on
supersonic flow devoid of quantitative measurements relating to the
effects of the viscosity and, in particular, with respect to the prop-
erties of the turbulence that was present.

The natural development now calls for information on turbulence in
supersonic wind tunnels Just as it was needed in the case of low-speed
wind tunnels in the last decade.