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1 2Z[ JK0 ¢£ S¤0 %+,-LM0 a¥¦2 §¨bp¡B0! ©ª«5ab#$¬ ae3¯°5±b 5 ! "²³%& x´µ} 2 ae 9!"#$%& ¶· *+ $ù RST%&26 \b *+ 7Ö î ×H288 789 7Ö î *+ 9:7 8C& ,;<=>2 8 9 a c? 0*+ 9:78C& @642789 7Ö09 \ 78 ABó x789 CD} ÞE5FGH/Na93ab a`p¡' "$1 9789ìí7/CD0EÞ*0N`9 78C& 9ab 0`3 I02J S¤0c f 134K0Ra93789L ¹# ì aeMN O;P5±b 8 8 9 a cd 5 H bS¤0QRóô078\bp¡¬ ae1W b010Sb Abstract Cavitation due to a suction vortex (vortex cavitation) is an important problem in some fluid machinery fields, such as fast reactors. In this study, a water experiment on vortex cavitation is carried out using a simple cylindrical vessel with a suction nozzle. In order to understand the fundamental behavior of vortex cavitation, its instantaneous occurrence behavior is grasped by visualization using high speed camera. Velocity distribution around vortex, which causes cavitation, is also quantitatively grasped by means of Particle Image Velocimetry. From visualization measurements, vortex cavitation is considered to be triggered by a wall nuclei and the cavity develops immediately toward the suction nozzle once triggering occurs on the bottom wall. In addition, distribution of pressure decrease along vortex center estimated based on Burgers model and measured velocity distribution shows monotone increase from the bottom wall toward the suction nozzle. As the results, the cavity is thought to develop toward the suction nozzle intake immediately, if some triggering of cavitation occur on the bottom wall.

Cavitation is a highly important issue in various fluid machineries. In the design of an advanced loop-type sodium-cooled fast reactor in Japan, vortex cavitation is also a significant issue for the integrity of the reactor structure. Thus, an evaluation method for vortex cavitation is required. In this study, vortex cavitation at a single suction pipe inlet was studied under several different viscosity conditions including its transient behavior. The intermittent occurrence behaviors of vortex cavitation were grasped by visualization measurements. The experimental results showed that the influence of the kinematic viscosity was obvious under a high kinematic viscosity. However, the influence became smaller with decreasing kinematic viscosity. From these results, the non-dimensional circulation, which was defined as the ratio of the local circulation to the kinematic viscosity, was deduced as an evaluation parameter to estimate the influence of the kinematic viscosity. Cavitation factors at transition points from continuous occurrence to intermittent occurrences were also evaluated as representative points where vortex cavitation occurs. Then, the occurrences of vortex cavitation were expressed as a relation between the cavitation factor at transition points and the non-dimensional circulation. As a result, it was clarified that the cavitation factor at transition points increased linearly in relatively small non-dimensional circulation, while it was nearly constant in relatively large non-dimensional circulation.