INSTRUMENTATION FOR THE MEASUREMENT OF HYDRODYNAMIC 
FLOW-NOISE 
by CHESTER L. WAKAMO, Associate Research Engineer, 
and ROBERT C, FITZPATRICK, Research Associate 
Institute of Science and Technology, The University of Michigan, 
Ann Arbor, Michigan 
ABSTRACT 
An experimental study of the generation of 
acoustic energy by fluid turbulence near an ex- 
tended solid boundary was performed. For this 
study, a free-falling self-contained missile was 
conceived. Parameters affecting the design of 
the vehicle were stability, velocity, recovery of 
the vehicle, skin vibration or "Self noise" fac- 
tor, and the effects of acceleration and decel- 
eration on equipment performance. An inboard 
magnetic tape data recording system stores the 
acoustic signals for subsequent analysis. De- 
tailed information on the depth-measurement cir- 
cuitry, automatic recovery mechanism, calibration 
procedure and check-out for a typical launching 
and recovery are presented. 
INTRODUCTION 
The study of acoustics is primarily con- 
cerned with the generation, transmission, and re- 
ception of energy in the form of pressure and 
velocity fluctuations. One particular aspect of 
this study is the process of generation of acous- 
tic energy by fluid turbulence near an extended 
solid boundary. Effects of boundary-layer tur- 
bulence are of special importance in high speed 
aircraft and missiles; torpedos, submarines, and 
surface ships. 
To measure the acoustic noise generated by 
boundary-layer turbulence the use of a missile 
type vehicle moving through water was considered. 
It was decided that a free-falling finless body 
with a self-contained electronic system to re- 
cord noise data was the best approach. Such a 
missile was designed, fabricated, and tested. 
The electronic system consisted of hydrophone 
transducers, a suitable magnetic-tape recorder, 
batteries for power, a pressure transducer to 
determine pressure and depth, and pressure-op- 
erated control switches. The vehicle was re- 
leased from a launching rack suspended just be- 
low the surface of the water. It would fall 
freely, with no ropes or cables attached, to a 
depth of no more than 500 ft. At some control- 
lable predetermined distance its descent was 
checked when the pressure-controlled switches 
caused the release of drag fins at the sides of 
the missile. As the deceleration produced by 
the drag fins occurred, switches shut off the 
recording system and released a bouyant tail sec- 
tion from the main body; this section rose to the 
surface, pulling with it a nylon recovery line 
which was unreeled from a spool secured to the 
main body. Figure 1 shows the missile in its 
launchirg frame. 
Preliminary tests were conducted at Orchard 
Lake, Michigan, a semi-private lake 40 miles 
northeast from Ann Arbor, chosen for its depth 
and relatively low background noise. A launch- 
ing platform was moored in 110 ft of water, per- 
mitting about 5 sec of flow-noise data from each 
drop of the missile. Provision was made to re- 
cord the depth during the missile descent by 
utilizing a pressure transducer and associated 
electronics. The depth record was later used to 
calculate the velocity. 
VEHICLE DESCRIPTION 
Parameters affecting the design of the 
vehicle were stability, velocity, recovery of 
vehicle, skin vibration or "self-noise" factor, 
and the effects of acceleration and deceleration 
on equipment performance. 
The vehicle consisted of 3 sections: a 
cast-aluminum nose, an extruded, tubular, alu- 
minum midsection, and a cast-aluminum tail 
(Fig. 2 and 3). 
The nose section was an ellipsoid of re- 
volution with the radius ratio a/b = 1.3, and 
dimensions of 7 in. and 10-3/4 in. A 100-1b 
lead ballast plug was bolted into the nose dur- 
