491 



decreasing and increasing cavitation number for 

 a = 172°. For decreasing a small cavitation bubbles 

 are obtained, which increase the noise level about 

 15 dB compared with increasing a. 



From the results at cavitation number a = 1.0 

 (see Figure 38) it is obvious that bubble cavitation 

 gives the largest increase in noise levels from 

 25 dB at low frequency (500 Hz) to 55 dB at high 

 frequency (40 kHz) . Sheet cavitation gives less 

 increase but depends on the intensity of the cavita- 

 tion. Thus for wing 16-12.12, a = -2°, the sheet 

 cavitation is extensive and gives an increase from 

 20 dB at low frequencies to 50 dB at high frequencies 

 compared with non-cavitating condition. For wing 

 K7 Vp3 the sheet cavitation is concentrated at the 

 leading edge and an increase in noise level is only 

 obtained for higher frequencies (> 2 kHz) and the 

 increase at 40 kHz is of the order of 25 dB. The 

 differences in noise level for wing K7 Vbl for 

 increasing and decreasing cavitation numbers can be 

 attributed to differences in cavitation patterns. 

 No pure vortex cavitation could be obtained at 

 cavitation number o = 1.0. 



noise level are obtained for higher frequencies 

 (f > 2 kHz) and for 40 kHz the increase is 25 dB. 

 Bubble cavitation gives the largest increases 

 in noise level. Levels are for this case 5 to 10 

 dB above the levels for sheet cavitation. 



ACKNOWLEDGMENT 



This work is part of the research program at the 

 Swedish State Shipbuilding Experimental Tank and 

 the authors are indebted to Dr. Hans Edstrand and 

 Mr. H. Lindgren for making this study possible. 

 Part of the work reported here has been carried 

 out with financial support from The Defence Material 

 Administration of Sweden. 



The authors would also like to express their 

 sincere thanks to those members of the staff at SSPA 

 who have taken part in the investigations and the 

 analysis of the material. 



Conclusions from Tests with Head Forms and Hydrofoils 



Tests with head forms are less suited as rather low 

 cavitation numbers are needed. This may cause 

 problems with high background levels due to undesired 

 cavitation on tunnel walls etc. Tests with hydrofoils 

 can be used to obtain effects on noise levels from 

 different types of cavitation. There may, however, 

 be some problems in obtaining pure cavitation types. 



Vortex cavitation gives an increase in noise 

 level of about 20 dB. It should be noted that 

 differences in vortex cavitation can be obtained 

 for increasing and decreasing pressure, which also 

 show as differences in noise level. Also a vortex 

 not attached to the wing causes increases in noise 

 level. The increase in noise level due to vortex 

 cavitation seems to be less for lower cavitation 

 numbers . 



Sheet cavitation gives siibstantially higher 

 levels than vortex cavitation. The extent of the 

 sheet has some influence on the noise level. For 

 a fairly large sheet increases in noise level of 

 20 dB at 500 Hz to 50 dB at 40 kHz are obtained. 

 For a small , leading edge sheet the increases in 



dB re 10'° Pa 

 150 



UO 



Cav number CJ"; 1 



130 



120 



110 



100 



Bubble and vortex 

 cav 116-12 12, a=172') 



Sheet cav. 

 (16-12.12, a= -2") 



Sheet cav. IK7 Vp 3 a=5 ) 

 Vortex and sheet cav. 

 increasing 0". 

 IK7 Vbl a = 5*l 



No cavitation 



05 



f UHz) 



FIGURE 38. Wings, cavitation noise (1/3 octave band). 

 (Free stream velocity 9 m/s , gas content 10%.) 



REFERENCES 



Baiter, J.-H. (1974). Aspects of Cavitation Noise. 

 Symposium on High Powered Propulsion of Large 

 Ships, Part 2, December 1974, Wageningen , The 

 Netherlands. Publication No. 490, Netherlands 

 Ship Model Basin, Wageningen, The Netherlands, 

 pp. XXV 1-39. 



Blake, W. K. , M. J. Wolpert, and F. E. Geib (1977). 

 Cavitation Noise and Inception as Influenced by 

 Boundary-Layer Development on a Hydrofoil. J. 

 Fluid Mech. 80, 4, pp. 617-640. 



Harrison, M. (1952). An Experimental Study of 



Single Bubble Cavitation Noise. J. Acoust. Soc . 

 Am. 24, 5; 776-782. 



Ito, T. (1962). An Experimental Investigation into 

 the Unsteady Cavitation of Marine Propellers. 

 Proceedings of lAHR- Symposium, Sendai, Japan, 

 1962, Cavitation and Hydraulic Machinery edited 

 by Numachi, F., Institute of High Speed Mechanics, 

 Tohoku University, Sendai, Japan, 439-459. 



Johnsson, C.-A. (1972). Cavitation Inception Tests 

 on Head Forms and Hydrofoils. Thirteenth Inter- 

 national Towing Tank Conference. Proceedings 

 Volume 1 edited by Schuster. S., and M. Schmiechen. 

 Versuchsanstalt fur Wasserbau und Schiffbau, 

 Berlin, Germany, 723-744. 



Lehman, A. F. (1966). Determination of Cavity 

 Volumes Forming on a Rotating Blade. Eleventh 

 International Towing Tank Conference, Tokyo 1966, 

 Proceedings edited by Kinoshita, M. , Yokoo, K. 

 The Society of Naval Architects of Japan, Tokyo, 

 Japan, 250-253. 



Levkovskii, Y. L. (1968). Modelling of Cavitation 

 Noise. Sov. Phys. -Acoust. 13, 3; 337-339. 



Rayleigh, Lord, (1917) . On the Pressure Developed 

 in a Liquid During the Collapse of a Spherical 

 Cavity. Phil. Mag. 34, 94-98. 



Ross, D. (1976). Mechanics of Underwater Noise. 

 Pergamon Press Inc., New York, USA, p. 218. 



Tanibayashi, H. , and N. Chiba (1977). Unsteady 



Cavitation of Oscillating Hydrofoil. Mitsubishi 

 Technical Bulletin 117. Mitsubishi Heavy 

 Industries, Ltd. Tokyo, Japan. 



