Publication detail

Experimental investigation of swirl number influence on spiral vortex structure dynamics

ŠTEFAN, D. HUDEC, M. URUBA, V. PROCHÁZKA, P. URBAN, O. RUDOLF, P.

Original Title

Experimental investigation of swirl number influence on spiral vortex structure dynamics

Type

conference paper

Language

English

Original Abstract

The hydraulic turbines are recently forced to operate far away from the optimal conditions in order to balance fluctuations in electricity generation. In case of Francis, pump and propeller turbines, using only single control component of guide vanes, it means that in regions where the high residual swirl enters the draft tube, the flow is decelerated and convenient conditions for the vortex rope development are created. Such flow conditions are considered to be the triggering mechanism for occurrence of different forms of vortex structures in the Francis turbine draft tube, e.g. spiral or straight vortex rope at part load or full load respectively. Independently on the vortex rope shape the unsteady pressure fields develop producing periodic stress on turbine components and possibly resulting in noise, blade cracks, runner lift, power swing, etc. To study and mimic such flow conditions, a simplified device of vortex generator apparatus is employed. Thanks to its design, the vortex generator enables to change the ratio between fluxes of axial momentum and tangential moment of momentum of generated swirl. Then, the behavior of vortex structure changes in a similar way as the flow rate variation in the draft tube of Francis turbine. For above mentioned reasons the unsteady cavitating spiral vortex is experimentally studied using both high speed video record and particle image velocimetry (PIV). The main focus is on change of vortex dynamics regarding to the swirl number variation. The proper orthogonal decomposition (POD) together with the classical fast Fourier transformation (FFT) are employed to extract dominant modes and frequencies from experimental data.

Keywords

vortex breakdown; vortex rope; PIV; swirling flow; swirl generator

Authors

ŠTEFAN, D.; HUDEC, M.; URUBA, V.; PROCHÁZKA, P.; URBAN, O.; RUDOLF, P.

Released

15. 6. 2021

Publisher

IOP Publishing

ISBN

1755-1307

Periodical

IOP Conference Series: Earth and Environmental Science

Year of study

774

Number

1

State

United Kingdom of Great Britain and Northern Ireland

Pages from

012085

Pages to

012085

Pages count

10

URL

https://iopscience.iop.org/article/10.1088/1755-1315/774/1/012085

Full text in the Digital Library

http://hdl.handle.net/11012/200962

BibTex

@inproceedings{BUT171994,
  author="David {Štefan} and Martin {Hudec} and Václav {Uruba} and pavel {procházka} and Ondřej {Urban} and Pavel {Rudolf}",
  title="Experimental investigation of swirl number influence on spiral vortex structure dynamics",
  booktitle="IOP Conference Series-Earth and Environmental Science",
  year="2021",
  journal="IOP Conference Series: Earth and Environmental Science",
  volume="774",
  number="1",
  pages="012085--012085",
  publisher="IOP Publishing",
  doi="10.1088/1755-1315/774/1/012085",
  issn="1755-1307",
  url="https://iopscience.iop.org/article/10.1088/1755-1315/774/1/012085"
}