E. J. Skudrzyk 201 
20 
PATCH DIAMETER (ft) 
Fig. 12.3. Patch diameter vs depth. 
PATCH DIAMETER = 2 x DEPTH 
(Urick —Searfoss data) 
Ke) 2 4 6 810 20 40 6080100 200 400 6001000 
DEPTH (ft) 
there is consolation in the factthata similar result has been obtained for patches 
of turbulence. The classical mixing length, which is equivalent to the radii of 
the turbulent patches, has been found to be 0.4 times the distance from the wall. 
The classical theory of turbulence did not satisfactorily explain this strange 
relationship, and this is probably the main reason for the rejection of this theory 
in recent years. The measurements of the temperature structure of water in- 
dicate that the classical mixing length is not just a mathematical artifice; it has 
physical significance and can be determined experimentally. 
The next important step in the study of the temperature structure of water 
is to determine the average temperature deviation between two points as a func- 
tion of their distance. This has been determined by L.C. Pharo [2] (Ordnance 
Research Laboratory), who used the thermistor bar shown in Fig. 12.4 to meas- 
ure temperature fluctuations. This bar, which is equipped with thermistors at 
distances of 1, 2, 4, 8, 16, 32, 64, and 128 in., led to impressive results. The - 
temperature fluctuation increases very little with the spacing between the ther- 
mistors. A closer study reveals that the rms temperature fluctuation increases 
with the cube root of the spacing (Fig. 12.5). If, for instance, the fluctuation is 
0.001° for a spacing of 10 cm, the rms temperature fluctuation increases to only 
1° for a spacing of 100 km. Again, a law that is similar to a well-known law in 
the theory of homogeneous turbulence has been confirmed. The rms fluctuation 
