부산대학교 도서관

The flow dynamics of the cavitating jet through poppet valves inevitably suffers from the influence of varying openness, but the relevant mechanism remains unclear. Hence, the present study conducts a numerical study on the cavitating flow phenomenon inside poppet valves with two valve seat structures, in order to examine the flow mechanisms underlying varying cavitation phenomenon at different openness. According to the results, the overall cavitation distribution as well as the morphology feature follows a similar pattern due to the same inception mechanism irrelevant of the openness amount. However, examination of the dynamic behaviors confirms discernable variation in 2 coupling effects between flow instability and cavitation. The flow separation at the poppet trailing edge produces non-cavitation flow instability at 0.4 mm openness and attached cavitation at 0.8 mm, which amalgamate with upstream-shed vortex cavitation. The stably attached cavitation within the chamfered groove at 0.4 mm, as the source of non-cavitation flow instability, and the detached cavitation at 0.6 and 0.8 mm openness produce vortex cavitation at the free shearing side. The substantial variation in these two coupling effects contributes sensibly to the increase in the overall cavitation intensity. Meanwhile, the weakened coupling effect between the free shearing vortex and wall shearing vortex, as a consequence of increased potential core thickness at larger openness, leads to the attenuated vortex cavitation at the wall poppet side. Additionally, the vortex cavitation at free shearing side has a larger size in the chamfered valve seat case, due to the coupling of shed flow instability with the Kelvin-Helmholtz instability. As a conclusion, the inception mechanism for the cavitation remains unchanged with openness, while the difference in flow instabilities as well as the associated coupling effects with cavitation contributes to the variation in cavitation intensity.