degree of such isotropic turbulence, namely "scale" and "intensity". 
[2 Generally, the intensity /@ is given as a percentage 
u 
where (ae is the root-mean-square of the velocity fluctuations, 
and U is the mean free-stream velocity. It has been found (1)* 
experimentally that the ratio U/¥ u* is practically independent 
of U, and that it increases behind a grid nearly linearly with the 
distance from the grid for values of X/M between 15 and 40. 
On the other hand, the scale, L, roughly defines the 
distance over which turbulent fluctuations are related. Strictly, 
it is a measure of the distance over which a correlation between 
velocity fluctuations exists. The correlation coefficient, R, is 
usually defined as R= U1 =3 where uj, and up are the velocity 
u 
u 
fluctuations at cee iL and 2,, In isotropic turbulence this may 
be written R = % since fu? =]u. The scale L is then defined as 
Cy u 
- Le fray, for measurements made in some direction y. Behind grids 
of various sizes, it has been found that L/M, where M is the mesh 
size is independent of U, but that it increases with the distance 
from the grid. 
In non-isotropic turbulence, such as the flow through a 
small pipe, the "intensity" and "scale" depend upon the direction 
under consideration and more independent parameters become necessary.. 
With these few remarks concerning parameters of turbulence 
we proceed to describe the several methods we have tried to use in 
measuring them. 
OIL INJECTION METHOD 
Several attempts have been made atthe Taylor Model 
Basin to devise methods of measuring L and ju? in water. The 
first was the photographic method reported in TMB Report C-13 
(2). In this test the flow of water through a lucite tube was 
photographed from two orthogonal planes, the flow being made 
visible by the injection of neutrally buoyant oil drops. Figure 
1 is an example of the record. The analysis of this non-isotropic 
turbulence consists in measuring the turbulence velocities. axially 
and radially, and statistically combining the results of at least 
500 drops. Since the tedium involved in analyzing the data 1s ex- 
cessive, the method is not recommendable. As yet, lack of time 
has prevented complete analysis of the records so obtained. 
* Numbers indicate references on page 8 of this report. 
Die 
