60 



for the solution of the hydrodynamical equations when the critical cavitation 

 numbers are specified. 



The cavitation method for developing forms having specified critical 

 cavitation numbers is based on the approximation of the minimum-pressure coef- 

 ficient as the negative of the critical cavitation number: 



/ P - P \ 



critical 



In this method, which was evidently first used by Reichardt 54 for designing 

 body shapes with essentially constant pressure surfaces for high speed air- 

 flight, the shape of a cavity formed behind an obstacle is used as the body 

 (see Figure 21a). It is clear that the method gives a restricted class of 

 forms — those having essentially constant pressures. The method has since been 

 used at the Taylor Model Basin for designing bodies with specified critical 

 cavitation numbers. 101 In the experiments of Reference 101 only axisymmetric 

 bodies were developed, but it is clear that other three- as well as two- 

 dimensional shapes may be developed depending upon the shape of the obstacles. 

 In actual design, the desired volume, length-diameter ratio, and general shape 

 will govern the selection of the obstacle. For example, the body shape de- 

 rived from cavities formed behind discs have larger length-diameter ratios 

 than those derived from hemispheres at the same cavitation number. 



A cavity with cavitation number 0.11 6 formed behind a disc is shown 

 in Figure 35 > a nd the body conforming to the cavity shape is shown in Figure 

 36, which was taken from Reference 101 . The pressure distribution on the re- 

 sulting body is shown in Figure 37- A discussion of the method of "closing" 

 the cavity to obtain the solid body, as well as the precautions which must be 



Figure. 35 - Cavity Formed Behind a Disc at Cavitation Number 0.11 6 



