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research-article

Study of pressure shock caused by a vortex ring separated from a vortex rope in a draft tube model

[+] Author and Article Information
Sergey G. Skripkin

Kutateladze Institute of Thermophysics Lavrentiev avenue 1, 630090, Novosibirsk, Russia
skripkin.s.g@gmail.com

Mikhail A. Tsoy

Kutateladze Institute of Thermophysics Lavrentiev avenue 1, 630090, Novosibirsk, Russia
miketsoy@gmail.com

Pavel A. Kuibin

Kutateladze Institute of Thermophysics Lavrentiev avenue 1, 630090, Novosibirsk, Russia
kuibin@itp.nsc.ru

Sergey I. Shtork

Kutateladze Institute of Thermophysics Lavrentiev avenue 1, 630090, Novosibirsk, RussiaNovosibirsk State University Pirogova Str. 2, 630090, Novosibirsk, Russia
shtork@itp.nsc.ru

1Corresponding author.

ASME doi:10.1115/1.4036264 History: Received September 08, 2016; Revised February 28, 2017

Abstract

Operating hydraulic turbines under part- or over-load conditions leads to development of the precessing vortex rope downstream of the turbine runner. In a regime close to the best efficiency point, the vortex rope is very unstable because of the low residual swirl of the flow. However, strong pressure pulsations have been detected in such a regime. These oscillations can be caused by self-merging and reconnection of a vortex helix with the formation of a vortex ring. The vortex ring moves along the wall of the draft tube and generates a sharp pressure pulse that is registered by pressure transducer. This phenomenon was investigated on a simplified draft tube model using a swirl generator consisting of a stationary swirler and a freely rotating runner. The experiments were performed at Reynolds number (Re) = 10^5. The measurements involved a high-speed visualization technique synchronized with pressure measurements on the draft tube wall, which enables an analysis of the key stages of vortex ring formation by comparing it with the pressure on the draft tube wall. Quantitative information regarding the average velocity distribution was obtained via the LDA technique.

Copyright (c) 2017 by ASME
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