VORTEX STRUCTURES AND CAVITATION ASPECTS AROUND A HOLLOW-JET VALVE

摘要

avitating vortex behaviors in the separated flow region behind the needle of a hollow-jet are investigated by both numerical and experimental methods. The moment aspects of the cavitating vortices in different cavitation conditions are observed by high-speed photographs. Unsteady viscous flows around the valve are simulated numerically by using an implicit SMAC scheme. It is found that the generations of cavitating vortices is related to the vortex motion in shear layer flow region of the separated flow. With a vortex formating, the pressure in the region decreases. In cavitation conditions, there are some cavitation bubbles occurred in the vortex formation area. A vortex forms a cavitating vortex by containing some bubbles. Typical cavitating vortices appear as circular bubble chains around the valve needle. However, in different cavitation conditions, the cavitating vortices in the separated flow region exhibit different aspects, namely, bubble chains, bubble cloud, and supercavitation, since the bubble number contained in a vortex is increased with the decreasing of the cavitation number. In splitter area, the typical cavitating vortices exhibit bubble masses which imping to the surfaces of splitters and collapse on it.