**7.2.1 Cavitation condition**

Fig.14 shows the cavitation conditions of the normal valve. These photographs were taken under the condition that the acrylic tube for visualization was illuminated by a metal halide light source and with a zoom lens and a bellows were attached to the high speed camera. The upper photographs show the whole of the butterfly valve cavitation, and the lower photographs show individual cavitation bubbles. The flow direction is from left to right. The lower photographs were taken at the position of 1.5 dia to the downstream direction from the butterfly valve center. The size of the visual field had a length of 1.3mm, and width of 6mm.

Under the inception condition shown in Fig 14(a), some bubbles were observed. There is a large bubble in the upper left, however the number of cavitation bubbles is little, and the diameter is also small.

Under the growth condition in Fig.14(b), the cavitation region extends to the 1.5dia downstream and the number of cavitation bubbles increase remarkably. Cavitation bubbles with diameters are from 20*m* to 200*m* were observed.

except for the near wall.

494 Mechanical Engineering

Fig.12. However, the noise of the Type-B was smaller than that of the normal valve. The

Figure 13(b) shows the cavitation noise in the flow of the biased velocity distribution (B). In this case, the cavitation noise was relatively smaller than that in the biased velocity distribution (A), but much larger than that in the normal distribution. However, the noise of the Type-B was smaller than that of the normal valve. Therefore, it is clear that the effect of the semi-circular fins holds even in the biased velocity distribution and that the cavitation

Fig.14 shows the cavitation conditions of the normal valve. These photographs were taken under the condition that the acrylic tube for visualization was illuminated by a metal halide light source and with a zoom lens and a bellows were attached to the high speed camera. The upper photographs show the whole of the butterfly valve cavitation, and the lower photographs show individual cavitation bubbles. The flow direction is from left to right. The lower photographs were taken at the position of 1.5 dia to the downstream direction from the butterfly valve center. The size of the visual field had a length of 1.3mm, and width

Under the inception condition shown in Fig 14(a), some bubbles were observed. There is a large bubble in the upper left, however the number of cavitation bubbles is little, and the

Under the growth condition in Fig.14(b), the cavitation region extends to the 1.5dia downstream and the number of cavitation bubbles increase remarkably. Cavitation bubbles

*m* were observed.

**7.2 Diameters and numbers of cavitation bubbles around the butterfly valves** 

(b) Cavitation Noise under biased velocity

50 , 13 )

distribution (

(a) Cavitation Noise under biased velocity

50 , 17 )

Fig. 13. Cavitation Noise under biased velocity distribution.

effect of the fins remained in the biased velocity distribution.

noise is larger when the velocity distribution is biased.

*m* to 200

distribution (A) (

**7.2.1 Cavitation condition** 

of 6mm.

diameter is also small.

with diameters are from 20

).

Under the flashing condition as shown in Fig.14(c), a large cavity was formed behind the valve, therefore the individual cavitation bubbles were not be able to be photographed
