Visualization of cavitation flow field downstream from an orifice

In order to understand the relationship between structures of flow fields and cavitation induced erosion and vibration, we carried out visualization of cavitation flow fields using a high speed camera and particle image velocimetry (PIV) downstream from an orifice in a pipe. In PIV measurements, we confirmed that at all cavitation numbers the reattachment location of flow from the orifice was at about 1.5 - 2.0 D downstream from the orifice outlet (where D= inner diameter of a pipe), and the flow direction near the wall was negative in the region of x < 1.5 D. In visualization of cavitation flow fields while changing the cavitation number, cavitation bubbles developed according to the decrease in cavitation number, and below σ = 0.9 a large number of cavitation bubbles reached near the pipe wall. These results indicated that the cavitation bubbles reached near the pipe wall at about 1.5 - 2.0 D downstream and they were carried by reverse flow along the pipe inner surface. Change of the bubble density near the pipe wall was largest at 1.5 - 1.6 D where erosion rate and vibration on the pipe outer surface were the maximum. (author)