TR No, 22 
3, The composite energy spectrum is of the form predicted by 
the Kolmogoroff hypothesis within the range of wave numbers from 
0.01 em™! to 0.026 cm™ ; at wave numbers greater than 0,026 cm” the 
energy spectrum decreases more rapidly than predicted because of at- 
tenuation of the higher wave number velocity variations, At wave 
numbers less than 0.01 cm7/ the turbulence is assumed anisotropic 
and inhomogeneous. The maxima in the individual energy spectra are 
located at wave numbers less than 0.003 cm. 
4, The average rate of energy dissipation by viscosity is estimated 
=-3 
as 0.84 cm*=sec ° 
5. The energy spectra are subject to a high noise level -- of the 
order of 20 cm3-sec™? -- resulting from random error in the digitized 
velocity data. The sources of error are an insufficiently high analog-to- 
digital conversion rate and insufficient sensitivity of the current meter 
combined with a large towing velocity compared to the variations in 
velocity. 
PLANNED RESEARCH 
Two much improved versions of the ducted impeller current meter are 
presently being considered for making additional turbulence measurements. 
The first is a Braincon Corporation Type 430 ducted impeller current meter, 
shown in figures 31 and 32. It is similar to the current meter used herein 
except that it is manufactured of type 316 stainless steel instead of brass, 
has a lighter weight impeller resulting in a smaller response distance, and 
has imporved bearings and hence increased sensitivity. The Type 430 current 
meter has approximately the same dimensions as the current meter used herein, 
and thus the high wave number response is similarly limited; the estimated 
useful wave number range is from 0 cm™~ to 0.04 cm ~, The primary advantage 
of the Type 430 current meter is its sensitivity, which is expected to result 
in a very low noise level. 
The second version is a Cox Instruments Model 12-SCRX turbine flow 
meter which was modified by machining off the pipe threads from the body 
(figures 33 and 34). The modified flow meter is 1.8 cm dia and 8.3 cm 
long. The advantages of the Cox unit are its small size, sensitivity 
(0.1% of mean flow), and simple disassembly for ball bearing replacement. 
o ° sll - 
The estimated wave number response range is 0 cm™~ to 0.1cm . 
27 
