Comparison of Cavitation Phenomena in Transparent Scaled-up Single-Hole Diesel Nozzles

The structure and evolution of cavitation in a transparent scaled-up diesel nozzle having a hole inclined at 90, 85, 80 and 0 degree to the nozzle axis has been investigated using high-speed motion pictures, flash photography and stroboscopic visualization. Observations revealed that at the inception stage, cavitation bubbles were not seen at the same locations in all the four nozzles. Cavitation bubbles grew intensively and developed into cloud-like structures. Shedding of the cloud cavitation was observed. When the flow was increased further the cloud-like cavitation bubbles developed into a dense large-scale cavitation cloud extending downstream of the hole. Under this condition the cavitation started mainly as a glassy sheet at the entrance of the hole. Until this stage the spray appeared to be symmetric. When the flow was increased beyond this stage, a sheet of cavitation covered a significant part of the hole on one side, extending to the hole exit. This non-symmetric distribution of cavitation within the hole resulted in a jet, which atomized on the side where more cavitation was distributed and non-atomizing on the side with less cavitation. The distribution of cavitation in the hole was different for different nozzles.