Fluid–structure interaction mechanisms leading to dangerous power swings in Francis turbines at full load

A. Müller, Arthur Tristan Favrel, C. Landry, F. Avellan

Research output: Contribution to journalArticle

26 Citations (Scopus)

Abstract

Hydropower plants play an important regulatory role in the large scale integration of volatile renewable energy sources into the existing power grid. This duty however requires a continuous extension of their operating range, provoking the emergence of complex flow patterns featuring cavitation inside the turbine runner and the draft tube. When the power output is maximized at full load, self-excited pressure oscillations in the hydraulic system may occur, which translate into significant electrical power swings and thus pose a serious threat to the grid stability as well as to the operational safety of the machine. Today's understanding of the underlying fluid–structure interaction mechanisms is incomplete, yet crucial to the development of reliable numerical flow models for stability analysis, and for the design of potential countermeasures. This study therefore reveals how the unsteady flow inside the machine forces periodic mechanical loads onto the runner shaft. For this purpose, the two-phase flow field at the runner exit is investigated by Laser Doppler Velocimetry and high-speed visualizations, which are then compared to the simultaneously measured wall pressure oscillations in the draft tube cone and the mechanical torque on the runner shaft. The results are presented in the form of a comprehensive, mean phase averaged evolution of the relevant hydro-mechanical data over one period of the instability. They show that the flow in the runner, and thus the resulting torque applied to the shaft, is critically altered by a cyclic growth, shedding and complete collapse of cavitation on the suction side of the runner blades. This is accompanied by a significant flow swirl variation in the draft tube cone, governing the characteristic breathing motion of the cavitation vortex rope.

Original languageEnglish
Pages (from-to)56-71
Number of pages16
JournalJournal of Fluids and Structures
Volume69
DOIs
Publication statusPublished - 2017 Feb 1
Externally publishedYes

Fingerprint

Francis turbines
Cavitation
Cones
Torque
LSI circuits
Unsteady flow
Two phase flow
Velocity measurement
Flow patterns
Turbomachine blades
Flow fields
Vortex flow
Turbines
Visualization
Hydraulics
Lasers

Keywords

  • Cavitation
  • Francis turbines
  • Full load
  • Laser Doppler Velocimetry (LDV)
  • Pressure surge
  • Self-oscillation
  • Swirling flows

ASJC Scopus subject areas

  • Mechanical Engineering

Cite this

Fluid–structure interaction mechanisms leading to dangerous power swings in Francis turbines at full load. / Müller, A.; Favrel, Arthur Tristan; Landry, C.; Avellan, F.

In: Journal of Fluids and Structures, Vol. 69, 01.02.2017, p. 56-71.

Research output: Contribution to journalArticle

@article{1c8677a0a28c42c598f5c56e811cc9d4,
title = "Fluid–structure interaction mechanisms leading to dangerous power swings in Francis turbines at full load",
abstract = "Hydropower plants play an important regulatory role in the large scale integration of volatile renewable energy sources into the existing power grid. This duty however requires a continuous extension of their operating range, provoking the emergence of complex flow patterns featuring cavitation inside the turbine runner and the draft tube. When the power output is maximized at full load, self-excited pressure oscillations in the hydraulic system may occur, which translate into significant electrical power swings and thus pose a serious threat to the grid stability as well as to the operational safety of the machine. Today's understanding of the underlying fluid–structure interaction mechanisms is incomplete, yet crucial to the development of reliable numerical flow models for stability analysis, and for the design of potential countermeasures. This study therefore reveals how the unsteady flow inside the machine forces periodic mechanical loads onto the runner shaft. For this purpose, the two-phase flow field at the runner exit is investigated by Laser Doppler Velocimetry and high-speed visualizations, which are then compared to the simultaneously measured wall pressure oscillations in the draft tube cone and the mechanical torque on the runner shaft. The results are presented in the form of a comprehensive, mean phase averaged evolution of the relevant hydro-mechanical data over one period of the instability. They show that the flow in the runner, and thus the resulting torque applied to the shaft, is critically altered by a cyclic growth, shedding and complete collapse of cavitation on the suction side of the runner blades. This is accompanied by a significant flow swirl variation in the draft tube cone, governing the characteristic breathing motion of the cavitation vortex rope.",
keywords = "Cavitation, Francis turbines, Full load, Laser Doppler Velocimetry (LDV), Pressure surge, Self-oscillation, Swirling flows",
author = "A. M{\"u}ller and Favrel, {Arthur Tristan} and C. Landry and F. Avellan",
year = "2017",
month = "2",
day = "1",
doi = "10.1016/j.jfluidstructs.2016.11.018",
language = "English",
volume = "69",
pages = "56--71",
journal = "Journal of Fluids and Structures",
issn = "0889-9746",
publisher = "Academic Press Inc.",

}

TY - JOUR

T1 - Fluid–structure interaction mechanisms leading to dangerous power swings in Francis turbines at full load

AU - Müller, A.

AU - Favrel, Arthur Tristan

AU - Landry, C.

AU - Avellan, F.

PY - 2017/2/1

Y1 - 2017/2/1

N2 - Hydropower plants play an important regulatory role in the large scale integration of volatile renewable energy sources into the existing power grid. This duty however requires a continuous extension of their operating range, provoking the emergence of complex flow patterns featuring cavitation inside the turbine runner and the draft tube. When the power output is maximized at full load, self-excited pressure oscillations in the hydraulic system may occur, which translate into significant electrical power swings and thus pose a serious threat to the grid stability as well as to the operational safety of the machine. Today's understanding of the underlying fluid–structure interaction mechanisms is incomplete, yet crucial to the development of reliable numerical flow models for stability analysis, and for the design of potential countermeasures. This study therefore reveals how the unsteady flow inside the machine forces periodic mechanical loads onto the runner shaft. For this purpose, the two-phase flow field at the runner exit is investigated by Laser Doppler Velocimetry and high-speed visualizations, which are then compared to the simultaneously measured wall pressure oscillations in the draft tube cone and the mechanical torque on the runner shaft. The results are presented in the form of a comprehensive, mean phase averaged evolution of the relevant hydro-mechanical data over one period of the instability. They show that the flow in the runner, and thus the resulting torque applied to the shaft, is critically altered by a cyclic growth, shedding and complete collapse of cavitation on the suction side of the runner blades. This is accompanied by a significant flow swirl variation in the draft tube cone, governing the characteristic breathing motion of the cavitation vortex rope.

AB - Hydropower plants play an important regulatory role in the large scale integration of volatile renewable energy sources into the existing power grid. This duty however requires a continuous extension of their operating range, provoking the emergence of complex flow patterns featuring cavitation inside the turbine runner and the draft tube. When the power output is maximized at full load, self-excited pressure oscillations in the hydraulic system may occur, which translate into significant electrical power swings and thus pose a serious threat to the grid stability as well as to the operational safety of the machine. Today's understanding of the underlying fluid–structure interaction mechanisms is incomplete, yet crucial to the development of reliable numerical flow models for stability analysis, and for the design of potential countermeasures. This study therefore reveals how the unsteady flow inside the machine forces periodic mechanical loads onto the runner shaft. For this purpose, the two-phase flow field at the runner exit is investigated by Laser Doppler Velocimetry and high-speed visualizations, which are then compared to the simultaneously measured wall pressure oscillations in the draft tube cone and the mechanical torque on the runner shaft. The results are presented in the form of a comprehensive, mean phase averaged evolution of the relevant hydro-mechanical data over one period of the instability. They show that the flow in the runner, and thus the resulting torque applied to the shaft, is critically altered by a cyclic growth, shedding and complete collapse of cavitation on the suction side of the runner blades. This is accompanied by a significant flow swirl variation in the draft tube cone, governing the characteristic breathing motion of the cavitation vortex rope.

KW - Cavitation

KW - Francis turbines

KW - Full load

KW - Laser Doppler Velocimetry (LDV)

KW - Pressure surge

KW - Self-oscillation

KW - Swirling flows

UR - http://www.scopus.com/inward/record.url?scp=85007247643&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85007247643&partnerID=8YFLogxK

U2 - 10.1016/j.jfluidstructs.2016.11.018

DO - 10.1016/j.jfluidstructs.2016.11.018

M3 - Article

AN - SCOPUS:85007247643

VL - 69

SP - 56

EP - 71

JO - Journal of Fluids and Structures

JF - Journal of Fluids and Structures

SN - 0889-9746

ER -