Cavitation (Influence of Free Gas Content) 
free stream turbulence, body boundary layer characteristics, and 
body pressure distribution are minimized. Specific studies were 
performed to evaluate the importance of headform surface nuclea- 
tion sources. Surface treatment procedures were designed to reduce 
the surface nucleation capability of the body. In this way the role of 
free stream nuclei could be more clearly defined. The actual gas bub- 
bles and solid particles just ahead of the headform were recorded 
by high speed holography. The path and stability of the bubbles as 
they passed over the body were determined analytically. These cal- 
culations were necessary to determine through what cross-sectional 
area upstream of the body all bubbles must pass if they are to con- 
tribute to the visually observed cavities on the body. The inception 
condition was measured acoustically and high speed movies were ta- 
ken to verify the type of cavitation present. The headforms tested 
consisted of several bodies each of plastic (Delrin)* and metal (copper 
and gold plated copper) materials, Cavitation tests on several bodies 
of the same material gives a check on the surface machining accura- 
cy and the material variety assists in evaluating the role of surface 
originating nuclei. The results of these water tunnel tests were com- 
pared with previous tests of the same bodies in the high speed towing 
basin. The significant aspects of the towing basin are that essential- 
ly no free gas bubbles are present and the turbulence levels are very 
low. From all of these studies the importance of free gas bubbles on 
acoustically measured cavitation inception can be evaluated for at 
least the headforms tested. 
In the interest of introducing into the cavitation literature re- 
cent research results from other disciplines pertinent to cavity nu- 
cleation, a review of this work will also be given. Specifically, these 
results demonstrate a mechanism by which stable hydrophobic parti- 
cles can be produced in water by the process of aeration, 
EXPERIMENTAL FACILITIES, INSTRUMENTATION, AND PROCE- 
DURE 
All of the experimental studies were carried out in the standard 
test facilities at NSRDC [6]. The cavitation inception studies to be 
reported here were performed in the 12-inch water tunnel using normal 
tap water filtered to remove particles larger than25 wm, Deaeration 
was accomplished by passing the water through a standard design pac- 
* Delrin, Acetal Resin, manufactured by E.I. Dupont de Nemours 
and Co., Wilmington, Delaware. 
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