Peterson 
ked column desorber. The test body used throughout the work was 
from the series tested by Rouse and McNown igah This is the same 
series from which the headform used for the ITTC comparative tests 
was selected [8]. The bodies tested had a minimum pressure coeffi- 
cient, ss Fe » equal to 0. 82, a diameter of 5 cm, and were installed 
in the water tunnel as shown in Figure 1. An axisymmetric headform 
was selected as the test body for several reasons, First, inception 
measurements are relatively straight-forward, because the body is 
stationary and it is easy to manufacture with a high degree of accu- 
racy. Secondly, vortex cavitation is not present. 
Cavitation inception was detected acoustically for all of the 
results presented here. The measurements were made by locating 
a hydrophone inside the headform on its axis. Details of the equip- 
ment and operational characteristics can be found in references [9] 
and fi O}. The noise level of the facility was determined for a tunnel 
pressure slightly above that corresponding to a cavitation inception 
number, g; , equal to “oe, . The associated electronics were then 
adjusted so that all cavitation noise exceeding the tunnel background 
level would be indicated. The cavitation inception number gj, is 
defined as 
Po 
a CER 
Ta 
-P 
g| = 
where P,, and Vg, are the upstream pressure and velocity respecti- 
vely, p is the density, and P,, the water vapor pressure. The cri- 
teria for the actual inception was selected to be one acoustic event 
per second. The technique of acoustic detection of inception will be 
considered in more detail later in this paper. 
The test procedure used in the water tunnel studies was to in- 
stall the headform and then deaerate the water to the desired total 
dissolved gas content. This dissolved gas content was measured with 
a standard van Slyke apparatus. All tests were run ata free stream 
velocity of 9.1 meters per second. The test section pressure was 
adjusted in stages to produce a range of cavitation conditions as mea- 
sured acoustically. When the cavitation inception pressure was rea- 
ched, a series of holograms were made of the bubbles and solid 
particles in the water just upstream of the body. High speed photo- 
graphy at 10,000 frames per second and 20 microsecond exposure 
time were also taken for selected runs at the inception conditions. 
1134 
