Johnson and Hsieh 



elliptic cylinders. For bodies having similar stagnation regions, we would 

 expect the screening effect to be less pronounced as c in is made more nega- 

 tive (for similar axial extent of the low-pressure region), because the larger 

 bubbles which are initially pushed out by the stagnation region are acted on by 

 the stronger negative pressure regions to return them. Clearly, Cp^^^ alone 

 is not adequate to define the magnitude of the screening effect; the entire pres- 

 sure distribution is necessary. 



Relative to suggestions as to how cavitation inception results from differ- 

 ent water tunnels may be compared, it is suggested that emphasis be given to 

 the development of instrumentation to determine the nuclei size spectrum in the 

 tunnel free-stream flow. Such information will contribute in a major way to the 

 definition of the true critical pressure for cavitation inception in a particular 

 facility and thus to corrections of the observed values of a-^ incipient to a value 

 based on some standardized critical pressure. 



182 



