481 



p 125 Pa/su 



iy,„#y,#«w>»'»,«l«*< 



fAf 



K*"' 



*/ 



,/ 



A^"'^'*'''^: 



fosc=7H2 



m p 265 Pa/su 

 o 



W=10Hz 



A miH\<%. 



p 265 Pa/su A| 



fosc=l^ Hz 



10 



15 t (ms) 



FIGURE 14. Pressure signals during collapse. Expanded 

 signals from Figure 10. 



p 26 Pa/su 



cimax 



i# 



# 



,1 (Ijiwiiy 



««l* 



rt* 



50 su 



W = IHz 



ii'm0u., , 



v''H,i; 



^a:l 



IV*,*' 



-»- Time 



82 Pa/su n 



''•■''^'» 



fosc = 2 Hz 





■■■''iy':::::.:"r 



/m^. 



82 Pa/su 



^:'"-V 





82 Pa/su 



131 Pq/su 



131 Pa/su 



A 'S ;\ A A 



,' V V:^ V ^./ V 



fosc = 3 Hz 



fosr = 4 Hz 



fosc = 7 Hz 



fosc = 10 Hz 



groups seldom collapsed exactly simultaneously 

 or with the same violence. For example, in 

 the cases shown in Figures 18 and 21 a part 

 of the cavities was cut off from the leading 

 edge during the last millisecond of the 

 collapse. This resulted in violent collapse 

 of the cut-off parts. 



From these examples it is understood that 

 in a single oscillation period the character 

 of the pressure signal is very sensitive to 

 such things as simultaneousness and violence 

 of separate cavitation events. Over many 

 periods, normally used in measurements, the 

 quantities are smoothed out to a mean value , 

 which often is less sensitive to small dis- 

 turbances . 



5. In some cases small bubbles and irregular 

 parts separated from the main cavity and 

 collapsed rather fast. In the case shown 



in Figure 22 a group of small bubbles behind 

 the main cavity (cavity B) collapsed violently, 

 simultaneously with the main cavity, and it 

 is impossible to determine which of the 

 cavities generated the main pulse. Examples 

 of cavities that seemed rather fast, but 

 only generated small pulses are shown in 

 Figure 18 (B) and 19 (C) . 



6. The most extensive rebounds resulted from 

 cavities that were cut off from the leading 

 edge and then collapsed fairly symmetrically. 

 The cut-off normally occurred during the 

 last one or two milliseconds and it often 

 resulted in two cavities , one of which 

 remained attached to the leading edge. The 



265 Pa/su 



fosc = U Hz 



FIGURE 15. Pressure signals from non-cavitating hydro- 

 foil, a = 3° a = 4°. 



Radiated pressure 



FIGURE 16. Schematic behavior of cavity volume and 

 radiated pressure. 



