**5. References**

Akmanov, A. G., Ben'kovskii, V. G., Golubnichii, P. I., Maslennikov, S. I., and Shemanin, V. G. (1974). Laser sonoluminescence in a liquid, *Soviet Physics Acoustics*, 19, pp.417-418.

Fig. 15. Images of the process of bubble collapse at γ = 1; the peak strength of the pressure wave is 520 kPa; the image time interval is 1/4000 second. The size of each individual frame

This study utilized a U-shape platform device to generate a single cavitation bubble and sequential images of the bubble collapse flow are recorded by a high speed camera for the detail analysis of the flow field characteristics and the cause of the counter jet during the process of bubble collapse induced by pressure wave. A series of bubble collapse flows induced by pressure waves of different strengths are investigated by positioning the cavitation bubble at different stand-off distances to the solid boundary. It is found that the Kelvin-Helmholtz vortices are formed when the liquid jet induced by the pressure wave penetrates the bubble surface. If the bubble center to the solid boundary is within one to three times the bubble's radius, a stagnation ring will form on the boundary when impacted by the penetrated jet. The liquid inside the stagnation ring is squeezed toward the center of the ring to form a counter jet after the bubble collapses. At the critical position, where the bubble center from the solid boundary is about three times the bubble's radius, the bubble collapse flows will vary. Depending on the strengths of the pressure waves applied, either just the Kelvin-Helmholtz vortices form around the penetrated jet or the penetrated jet impacts the boundary directly to generate the stagnation ring and the counter jet flow. This phenomenon used the particle image velocimetry method can be clearly revealed the flow field variation of the counter jet. If the bubble surface is in contact with the solid boundary, the liquid jet can only splash radially

For all the experiments performed in this study, the strength of the pressure wave adopted to induce the bubble collapse flow was kept as low as possible so that the bubble collapsed in a longer period of time. The characteristics of the bubble collapse flows at different standoff distances can thus be clearly manifested. However, different strengths of the pressure waves are needed to induce the bubble collapse flow at different γ locations. A lower

Akmanov, A. G., Ben'kovskii, V. G., Golubnichii, P. I., Maslennikov, S. I., and Shemanin, V. G. (1974). Laser sonoluminescence in a liquid, *Soviet Physics Acoustics*, 19, pp.417-418.

strength of the pressure wave is needed for an increasing γ value and vice versa.

is 6.2 mm 3.1 mm. Rmax is 2.25 mm. Lower Part: sketch of the liquid jet position.

without producing the stagnation ring and the counter jet.

**4. Conclusions** 

**5. References** 


**21** 

*Japan* 

Kazuhiko Ogawa *Osaka Sangyo University,* 

**Noise Reduction in Butterfly Valve** 

 **Visualization of Cavitation Flow** 

 **Cavitation by Semicircular Fins and** 

Butterfly valves have the advantage of being very compact and simple to install compared with other types of valves, and so they are widely used in industry. However, depending on the conditions, cavitation may occur around a butterfly valve. When severe noise and vibration occur because of cavitation around a butterfly valve, the valve body and pipe wall

Butterfly valves are sometimes used inside the piping of air-conditioning facilities and the noise and vibration caused by cavitation can, in addition to making users uncomfortable, be mistaken for mechanical trouble. The need to prevent such noise and vibration is increasing from an environmental standpoint, and the prevention or suppression of cavitation itself is very important. Accordingly, many products have been proposed to prevent or control cavitation around many types of valves (Baumann,1991; Tullis,1989). As for research on the prevention of cavitation, the characteristics of a control valve with tortuous paths and an orifice with a multi-perforated cone to prevent cavitation from occurring around the orifice

These methods have already been applied to actual products, and those products have proved very successful in reducing noise. However, tortuous path valves, for example, are applicable only to cases wherein the fluids are clean and the shapes of the piping arrangements around the valves are complicated. Moreover, the air injection method that is very effective in reducing cavitation is limited to cases wherein the effect of air can be ignored. Hence, the authors proposed the sudden enlargement of a pipe downstream of a butterfly valve (Ogawa & Uchida,2005). This method was much simpler than the conventional methods. However, the sudden enlargement of the pipe is not adequate for flows containing particles because the

The author has already proposed the attachment of fins to the valve body in order to further reduce cavitation noise around the butterfly valve (Ogawa & Uchida,2005, Ogawa,2008). This method can be used for flows containing particles because of the simple shape of the valve body. Cavitation occurs intensely around the butterfly valve because of the interference of the flow from the nozzle side with the flow from the orifice side (Itoh et

**1. Introduction** 

are subjected to erosion.

were reported.(Rahmaeyer et al.,1995; Kugou,1996)

particles accumulate in the enlarged section of the pipe.

