490 



Wing 16-12 12 

 Elliptic , cambered 



dB re lO'" Pa 

 150 



Wing K7 



Trapezoidal , symmetric 



Tip shape ; 

 R(3unded K7 Vb 1 



End plate K7 Vp 3 



FIGURE 35. Wings' 



Results from the tests are given here for five 

 cavitation numbers, a = 3, 2.5, 2, 1.5, and 1. 

 The free stream velocity was 9 m/s and the gas 

 content ratio was 10^. Results are given as faired 

 curves for the noise levels from 1/3 octave band 

 analysis. 



For cavitation number a = 3 (Figure 36) only 

 the cambered wing 16-12.12 at a = 172° cavitates 

 with vortex cavitation. Noise levels for the wings 

 with no cavitation are of the same order as for the 

 empty tunnel. The vortex cavitation at a = 172° 

 gives an increase in noise levels of 15 to 20 dB 

 compared with non-cavitating conditions. 



At a = 2.5 the wing 16-12.12 has vortex cavita- 

 tion at a = 2° and a = 172°, Figure 36. It is of 

 interest to note that the vortex cavitation at 

 a = 2° is not attached to the wing tip but starts 

 behind the wing. This vortex can only be obtained 

 when the pressure in the tunnel is increased 

 (increasing cavitation number) . The increase in 

 noise level due to vortex cavitation here is also 

 15 to 20 dB. 



For the cavitation number a = 2 the wing 16-12. 

 12 has vortex cavitation at a = 172°, intermittent 

 vortex cavitation at a = 2° and sheet cavitation 

 at a = -2°. The vortex cavitation gives an increase 

 in noise level of the order of 15 dB. The sheet 

 cavitation at a = -2° increases the noise levels 

 at higher frequencies (f > 5 kHz), 10 to 15 dB 

 above the level for vortex cavitation, see Figure 

 37. 



At a = 1.5 it can be noted that in some cases 

 no pure types of cavitation can be obtained. Thus, 

 wing 16-12.12 gives sheet cavitation at a = -2°, 

 vortex cavitation at a = 2° and vortex and bubble 

 cavitation at a = 172°. Results in Figure 37 show 

 the largest increase of noise levels for sheet 

 cavitation. Note also the differences between 



Cav number 0- 3 



12.12 , a=172 ) 



4ff f(kHz) 



dB re 10'* Pa 

 150 r 



KO 



130 



120 



100 



Cav number (S- 2 5 



-Vortex cav. 116-12.12 , 

 -Vortex not V a=172°, a=2°) 



attached (a=2') 



No cavitation 



" ID fTkHz) 



FIGURE 36. Wings, cavitation noise (1/3 octave band). 

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



dB re 10'° Pa 

 150 



Cav. number CJ= 2 



Sheet cav. (16-12 12, a= -2 



Vortex cav (16-12 12, 



a = 172°, a=2°) 



40 f(kHz) 



dB re 10 ■" Pa 

 150 



Cav number <S - 1 5 



-Sheet cav (16 -12 12 , a= - 2") 



Vortex and bubble - 

 cav decreasmg . 

 116-12 12 , a=172' 



(16-12 12,a=172 

 (J increasing ,Ct= 2 ) 



40 f(kHz) 



FIGURE 37. Wings, cavitation noise (1/3 octave band). 

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



