A novel scenario of aperiodical impacts appearance in the turbine draft tube

28th IAHR symposium on Hydraulic Machinery and Systems

Alekseenko, S.V.^1 ; Kuibin, P.A.^1 ; Shtork, S.I.^1 ; Skripkin, S.G.^1 ; Sonin, V.I.^2 ; Tsoy, M.A.^1 ; Ustimenko, A.S.^2

Kutateladze Institute of Thermophysics SB RAS, 1 Lavrentyev Ave., Novosibirsk

630090, Russia^1

Branch of Power Machines - JSC Leningradsky Metallichesky Zavod, Sverdlovskaya nab. 18, St.-Petersburg

195009, Russia^2

关键词: Best efficiency point;    Cavity collapse;    Experimental research;    Helical vortices;    High-speed video;    Hydroturbines;    Low frequency pressure;    Pressure impact;   

Others  :  https://iopscience.iop.org/article/10.1088/1755-1315/49/8/082025/pdf
DOI  :  10.1088/1755-1315/49/8/082025

来源: IOP

【 摘 要 】

The swirling flow in the discharge cone of hydroturbine is characterized by various self-induced instabilities and associated low frequency phenomena when the turbine is operated far from the best efficiency point. In particular, the precessing vortex rope develops at part-load regimes in the draft tube. This rope can serve a reason of the periodical low- frequency pressure oscillations in the whole hydrodynamical system. During the experimental research of flow structure in the discharge cone in a regime of free runner new interesting phenomenon was discovered. Due to instability some coils of helical vortex close to each other and reconnection appears with generation of a vortex ring. The experiments were fulfilled at the cavitational conditions when a cavity arises in the vortex core. So the phenomenon was registered with help of visualization by the high speed video recording. The vortex ring after the reconnection moves apart from the main vortex rope toward the wall and downstream. When it reaches the area with high pressure the cavity collapses with generation of pressure impact. The mechanism of cavitational vortex rings generation and their further collapse can serve as a prototype of the aperiodical pressure impacts inside the turbine draft tube.