A simple series heating circuit similar to that of Fig- 
ure 2 was used to heat the wires. A current of 1.0 ampere was 
maintained, and the fluctuating voltage output of the wires was 
amplified and recorded by a string oscillograph. No compensation 
for thermal lag was used. : 
Definite evidence of transition was detected on one of 
the two wires located at the midlength of the plane. A sample of 
the record is given in Figure 9. The record which may be expected 
from mixed or transitional flow is typified by Figure 9(c). At 
higher speeds it is seen that the flow was turbulent, being char- 
acterized by higher frequency and the expected smaller amplitude 
fluctuations resulting from lack of compensation. 
Similar experiments have been conducted on a ship model 
with equal success. The hot wire, therefore, can be used in this 
manner to distinguish qualitatively between laminar and turbulent 
flow. Measurement of scale and intensity of the turbulence in 
boundary layers in being considered, and such results should pro- 
vide significant information regarding the accuracy of present 
methods of artificially creating turbulent boundary layers by 
various size rods placed ahead of the model being towed. 
DYE DIFFUSION METHOD OF MEASURING TURBULENCE 
A third method of measuring turbulence intensity, which 
depends upon the diffusion by turbulence of a dye injected into 
the stream, has been tried in the model channel, A fine brass rod 
replacing one of the strands of a }-inch mesh, and bent in the 
form of an L extending 15 mesh lengths downstream was used as an 
injector of a water solution of red dye.. A similar rod attached 
to a pipette served as a sampler probe. With the channel operating 
at a speed of about 1 knot, cross-stream surveys by sampling the 
water were made at distances of 4, 3/4, and 1 inch from the nozzle 
of the injector. The concentration of the samples of each survey 
was compared with the original concentration of dye by means of an 
electrophotometer. The boundary of the diffusing dye wake, defined 
as the standard deviation of the cross-stream distribution of dye 
concentration was determined at the three stations. The slope of 
the boundary so determined was applied to determine the value of 
the turbulence intensity in the region of the dye injector nozzle. 
In Figure 8 the result of the experiment is seen to agree, in order 
of magnitude, with the hot wire results. Since the experiment was 
carried out in a rather crude fashion, better agreement was not 
expected. 
CONCLUSION 
Since the measurement of turbulence in water is still 
in its preliminary stages, it is impossible to discuss any real 
=~ 7 = 
