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Research Papers: Flows in Complex Systems

Study of Pressure Shock Caused by a Vortex Ring Separated From a Vortex Rope in a Draft Tube Model

[+] Author and Article Information
S. G. Skripkin

Department of Heat Power Engineering,
Kutateladze Institute of Thermophysics,
Lavrentiev Avenue 1,
Novosibirsk 630090, Russia
e-mail: skripkin.s.g@gmail.com

M. A. Tsoy

Department of Heat Power Engineering,
Kutateladze Institute of Thermophysics,
Lavrentiev Avenue 1,
Novosibirsk 630090, Russia
e-mail: miketsoy@gmail.com

P. A. Kuibin

Department of Physical Hydrodynamics,
Kutateladze Institute of Thermophysics,
Lavrentiev Avenue 1,
Novosibirsk 630090, Russia
e-mail: kuibin@itp.nsc.ru

S. I. Shtork

Department of Heat Power Engineering,
Kutateladze Institute of Thermophysics,
Lavrentiev Avenue 1,
Novosibirsk 630090, Russia;
Laboratory for Simulations of Processes
in Energy Engineering,
Novosibirsk State University,
Pirogova Street 2,
Novosibirsk 630090, Russia
e-mail: shtork@itp.nsc.ru

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received September 8, 2016; final manuscript received February 28, 2017; published online May 18, 2017. Assoc. Editor: Riccardo Mereu.

J. Fluids Eng 139(8), 081103 (May 18, 2017) (7 pages) Paper No: FE-16-1587; doi: 10.1115/1.4036264 History: Received September 08, 2016; Revised February 28, 2017

Operating hydraulic turbines under part- or over-load conditions leads to the development of the precessing vortex rope downstream of the turbine runner. In a regime close to the best efficiency point (BEP), the vortex rope is very unstable because of the low residual swirl of the flow. However, strong pressure pulsations have been detected in the 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) = 105. 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 laser Doppler anemometer (LDA) technique.

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Figures

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Fig. 1

Schematic view of experimental closed-loop test rig (a), scheme (b), and sketch (c) of the working area

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Fig. 2

Dimensionless аxial and tangential mean velocity, Q = 0.018 m3 s−1, dashed line denotes zero velocity

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Fig. 3

Dimensionless pulsations of axial and tangential velocities, Q = 0.018 m3 s−1

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Fig. 4

Process of vortex ring formation and synchronized fluctuation of wall pressure; additional evacuation 20 kPa, Q = 0.042 m3 s−1

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Fig. 5

Another pattern of vortex ring formation; additional evacuation 7 kPa, Q = 0.042 m3 s−1

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Fig. 6

Two scenarios of vortex ring formation: the isolated vortex ring (left) and the linked vortex ring (right)

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Fig. 7

Geometrical parameters of a vortex rope in a basic state

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