498 



IdB 



- Bodel-tcMt dmta 



o o - full-seal* tast data 



FIGURE 6. Comparison of noise levels extrapolated 

 from model with measured full-scale data in a wide 

 band of frequencies. 



and T - L. The table below shows extrapolators for 

 scaling the square of the acoustic pressure during 

 cavitation from model to full-size with reference 

 to the assumptions of constant and variable coeffi- 

 cients of cavity energy transformation into noise, 

 Tif and to fit the cases of constant Froude number 

 and constant absolute pressure. 



That the frequencies vary inversely in proportion 

 to linear dimensions in modelling at a constant 

 pressure may turn out to be a significant advantage, 

 so the acoustic wave lengths change in proportion 

 to linear dimensions of the model and wave inter- 

 ference patterns remain unchanged. In modelling by 

 the Froude method wave lengths on the model are 



IdB 



O model-test and full-scale results for the wide 



frequency band 

 • model-test and full-scale results for the 1/3- 



octave noise frequency band of the model - 80 kHz 



instant of visual detection of vortex cavitation 

 on the model 



FIGURE 7. Comparison of noise levels extrapolated 

 from model with measured full-scale data. 



TABLE 1. Cavitation Noise Levels Scaling 

 Extrapolator 



P P 



_ o _ o 



n = — n 



n = const L T 



F = const 



T 



P = const 

 o 



lV2 

 1 



lV2 

 1/L 



L^ 

 1/L 



known to be v'L times larger than the model linear 

 dimensions. 



Figure 6 shows the comparison between the model- 

 test data (solid line) scaled the comparison between 

 the model-test scale data (dotted line) for the 

 noise level in a wide band of frequencies. Figure 

 7 gives a similar comparison with another prototype. 

 Curves of cavitation noise increase are also compared 

 in a 1/3-octact band for the model at the frequency 

 of 80 kHz. In Figure 7 the moment of visual detec- 

 tion of cavitation is marked on the general level 

 curve with an asterisk. Full-scale data are given 

 here for individual rates of speed. 



The scaling extrapolator (8) needs to be verified 

 under full-scale conditions and is likely to be 

 refined. However, the need for stability of the 

 coefficient of cavity energy transformation into 

 cavitation noise appears to be an indisputable 

 argument for cavitation noisiness scaling with the 

 full-scale pressure retained. 



CONCLUSION 



The two major conclusions can be formulated as 

 follows : 



- Scaling for cavitation noise measurements with 

 the full-scale pressure retained gives a high value 

 coefficient of cavity energy transformation into 

 noise and substantial advantages in respect to: 



a) obtaining high levels of cavitation noise; 



b) similarity of sound waves to the model. 



- Large-scale modelling with the full-scale 

 pressure retained confirmed the possibility brought 

 out by the analysis of an elementary cavitation 

 process of acoustic detection of cavitation long 

 before the cavity reaches the size that can be 

 detected visually. 



REFERENCES 



Beniaminovich, M. B., K. A. Kondratovich, and I. V. 

 ICrutetsky (1975) . On experimental determination 

 of acoustic radiation energy during cavitation 

 bubble collapse. (in Russian) . Symposium on 

 Physics of Acoustics-Hydrodynamics Phenomena, 

 Reports, Izd. "Nauka" , Moscow. 



Goncharov, 0. N. , A. S. Gorshkoff, and V. J. Vaniu- 

 khin (1977) . Cavitation and its noise radiation 

 in steady and unsteady flows. 9th All-Union 



