The nozzle coefficient for the high velocity (0.569 foot per second) was 
then calculated to be 0.99. This set of measurements was repeated for 
a low flow rate. The results of these measurements are shown in Figure 
21(b). The nozzle coefficient for the low velocity (0.072 foot per sec- 
ond) was calculated'to be 0.98. The nozzle coefficient for intermediate 
velocities was assumed to be a linear interpolation between the two above 
values. 
c. Flume Measurements of Turbulent Velocity Distributions. The 
velocity, which is of significance in attempting to describe the sus- 
pension of sediment in an oscillating flow, is the vertical component of 
velocity fluctuations due to turbulence, v'. When the swing flume is 
operating, the only velocities which exist in the fluid are: (a) the 
three directional components of velocity fluctuations caused by turbu- 
lence, and (b) the oscillating flow contained in the boundary layer. 
The boundary layer extends only a few millimeters above the bed of the 
flume. Sediment is in suspension at an elevation considerably above 
the upper limit of the boundary layer. Therefore, the flow regime of 
interest has no measurable mean or periodic velocities, only the random 
motions caused by the turbulence diffusing upward from the bed. The 
problem, then, is to determine only the vertical component of the veloc- 
ity fluctuations. 
Das (1968) developed a method of measuring v' in a still body of 
water with an oscillating rough bed. This method involved imparting an 
oscillating motion to the sensor in the vertical direction. If only 
measurements made during the peak velocity of the sensor are considered, 
then the total velocity affecting heat transfer from the sensor is: 
v2 = (V + vt)? + ut? + wi2 - (16) 
where 
Ve = total velocity affecting heat transfer 
Vv = peak velocity of the sensor; known from the period and 
amplitude of oscillation 
Vie = vertical component of the turbulent velocity fluctuations 
u' and w' = turbulent velocity fluctuations in the remaining two 
directions 
Dividing this equation by v2 yields: 
CES We GNM ee ICON Ca De. (a7) 
If the sensor oscillation is such that V >> v', u', and w', then the 
above equation can be approximated by: 
CENA Osean” (18) 
53 
