• Version
• 39 Downloads
• 3.09 MB File Size
• 1 File Count
• November 2, 2016 Create Date
• November 2, 2016 Last Updated

National Advisory Committee for Aeronautics, Report - Development of Turbulence Measuring Equipment

Hot-wire turbulence-measuring equipment has been developed
to meet the more stringent requirements involved in the measure-
ment of fluctuations inflow parameters at supersonic velocities.
The higher mean speed necessitates the resolution of higher
frequency components than at low speed, and the relatively 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.
Oomtant—current operation is employed. Compensation for
hot-wire lag is adjusted manually using square-wave testing to
indicate proper setting. These and other features malae the
equipment adaptable to all-purpose turbulence work with im-
proved utility and accuracy over that of older types of equip-
ment. 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 supersonic 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
properties of the turbulence that was present.

The natural development calls for information on turbu—
lence in supersonic wind tunnels just as it was needed in the
case of low-speed wind timnels in the last decade.

The feasibility of using hot-wires in a supersonic flow was
first demonstrated by Dryden and Schubauer in 1946, when
they operated a 0.0003—inch-diameter tungsten wire in the
Aberdeen wind tunnel and observed fluctuations with it.
(This work is unpublished.) This type of measurement was
repeated in the Langley 9-inch supersonic tunnel at Langley
Field in late 1947.