TM No. 377 



During all of the towing experiments, the tank was filled with standard 

 tap water at a temperature of about l6°C and having a density of 0.99^9 gm cm""^, 



Calibration of Individual Ducted Meters. The first towing tests were 

 conducted to determine the response of the individual ducted meter to fluid 

 flow simulated by various steady towing speeds. Of particular interest is 

 the difference in impeller response for forward and backward motion through 

 the cylinder, and also the differences in calibration between the two meters. 



The individual ducted meter was mounted on the tow carriage as shown in 

 figure II-18. The meter was mounted on a brass pipe (shown in the inverted 

 position) upon which was fixed a circular disc inscribed with angular marks 

 at 5-degree increments. The pillbox containing the potted induction coil 

 was locked with screws into the center hole of the angle-measuring disc. The 

 cylinder and disc could be rotated about 36O with respect to t he towing 

 direction marker fixed rigidly to the suspension column. This column was 

 braced to a heavy plywood support, which in turn was bolted to the towing 

 carriage. The two Mecca connector cables were led from the pillbox into 

 the support column and out through a hole near the base. During the towing 

 these signal leads were connected to a 20-meter length of "shielded pair" 

 which led to the recorder. This long connecting lead was then strung the 

 length of the tank so that it could easily follow as the carriage was driven 

 back and forth. 



The first series of tests involved the towing of each meter (mounted 

 individually) at various steady speeds. The cylinder axis was parallel 

 to the towing axis of the tank. Runs of the carriage were made in both 

 directions along the tank, simulating positive and negative flows. 



The results of the steady towing tests are depicted in figure 11-21 , 

 The curve (dots) shows the frequency of voltage pulses f, in cps versus the 

 towing speed in cm sec" 1 for the individually mounted meters. The range of 

 tow speeds was from 6.7 cm sec" 1 through 210.8 cm sec" 1 (not shown in figure 

 11-21). A complete tabulation of the experimental data is given in appendix B. 



In figure 11-21 it is difficult, if not impossible, to distinguish between 

 points derived from "down tank" runs and those derived from "up tank" runs. 

 It is also difficult to distinguish between points from each of the two meters. 

 The tightness and linearity of the curve establish the similarity in response 

 of the two meters. 



An attempt was made to determine the minimum tow speed at which the 

 impeller responds. This threshold speed was found to be between 6,6 and 

 7.5 cm sec" 1 (in either direction) for both meters. 



In the upper range of speeds, the impellers appeared to respond in the 

 same linear fashion. 'There was no indication of an abrupt change in the 

 shape of the curve (even for speeds as high as 140-160 cm sec" 1 ), indicating 

 a marked stability over the range of speeds tested. At the extreme high 

 speeds, the meter produced visible surface "bow" waves as it was towed 



35 



