Renewable energy sources (RES) have reached 23.7% of the worldwide electrical generation production in 2015. The hydraulic energy contribution amounts to 16.6% and comes mainly form large-scale hydropower plants, where Francis turbines represents 60% of the generating units. However, the future massive development of RES will require more advanced grid regulation strategies that may be achieved by increasing the operation flexibility of the Francis generating units. Part load operating condition of these turbines is hindered by pressure fluctuations in the draft tube of the machine. A precessing helical vortex rope develops in this condition, which imperils the mechanical structure and limits the operation flexibility of these turbines. A thorough description of the physical mechanism leading to the vortex rope is a prerequisite to develop relevant flow control strategies. This work, based on a linear global stability analysis of the time-averaged flow field, including a turbulent eddy viscosity, interprets the vortex rope as a global unstable eigenmode. In close resemblance to spiral vortex breakdown, a single-helix disturbance develops around the time-averaged flow field and growths in time to finally form the vortex rope. The frequency and the structure of this unstable linear disturbance are found in good agreement with respect to the three-dimensional (3D) numerical flow simulations.
Skip Nav Destination
Article navigation
Research-Article
Part Load Vortex Rope as a Global Unstable Mode
Simon Pasche,
Simon Pasche
Department of Mechanical Engineering,
Laboratory for Hydraulic Machines,
Swiss Federal Institute of Technology (EPFL),
Avenue de Cour 33bis,
Lausanne CH-1007, Switzerland
e-mail: simon.pasche@alumni.epfl.ch
Laboratory for Hydraulic Machines,
Swiss Federal Institute of Technology (EPFL),
Avenue de Cour 33bis,
Lausanne CH-1007, Switzerland
e-mail: simon.pasche@alumni.epfl.ch
Search for other works by this author on:
François Avellan,
François Avellan
Professor
Department of Mechanical Engineering,
Laboratory for Hydraulic Machines,
Swiss Federal Institute of Technology (EPFL),
Avenue de Cour 33bis,
Lausanne CH-1007, Switzerland
e-mail: francois.avellan@epfl.ch
Department of Mechanical Engineering,
Laboratory for Hydraulic Machines,
Swiss Federal Institute of Technology (EPFL),
Avenue de Cour 33bis,
Lausanne CH-1007, Switzerland
e-mail: francois.avellan@epfl.ch
Search for other works by this author on:
François Gallaire
François Gallaire
Professor
Department of Mechanical Engineering,
Laboratory of Fluid Mechanics and Instabilities,
Swiss Federal Institute of Technology (EPFL),
Lausanne CH-1015, Switzerland
e-mail: francois.gallaire@epfl.ch
Department of Mechanical Engineering,
Laboratory of Fluid Mechanics and Instabilities,
Swiss Federal Institute of Technology (EPFL),
Lausanne CH-1015, Switzerland
e-mail: francois.gallaire@epfl.ch
Search for other works by this author on:
Simon Pasche
Department of Mechanical Engineering,
Laboratory for Hydraulic Machines,
Swiss Federal Institute of Technology (EPFL),
Avenue de Cour 33bis,
Lausanne CH-1007, Switzerland
e-mail: simon.pasche@alumni.epfl.ch
Laboratory for Hydraulic Machines,
Swiss Federal Institute of Technology (EPFL),
Avenue de Cour 33bis,
Lausanne CH-1007, Switzerland
e-mail: simon.pasche@alumni.epfl.ch
François Avellan
Professor
Department of Mechanical Engineering,
Laboratory for Hydraulic Machines,
Swiss Federal Institute of Technology (EPFL),
Avenue de Cour 33bis,
Lausanne CH-1007, Switzerland
e-mail: francois.avellan@epfl.ch
Department of Mechanical Engineering,
Laboratory for Hydraulic Machines,
Swiss Federal Institute of Technology (EPFL),
Avenue de Cour 33bis,
Lausanne CH-1007, Switzerland
e-mail: francois.avellan@epfl.ch
François Gallaire
Professor
Department of Mechanical Engineering,
Laboratory of Fluid Mechanics and Instabilities,
Swiss Federal Institute of Technology (EPFL),
Lausanne CH-1015, Switzerland
e-mail: francois.gallaire@epfl.ch
Department of Mechanical Engineering,
Laboratory of Fluid Mechanics and Instabilities,
Swiss Federal Institute of Technology (EPFL),
Lausanne CH-1015, Switzerland
e-mail: francois.gallaire@epfl.ch
Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received March 11, 2016; final manuscript received December 22, 2016; published online March 16, 2017. Assoc. Editor: Kwang-Yong Kim.
J. Fluids Eng. May 2017, 139(5): 051102 (11 pages)
Published Online: March 16, 2017
Article history
Received:
March 11, 2016
Revised:
December 22, 2016
Citation
Pasche, S., Avellan, F., and Gallaire, F. (March 16, 2017). "Part Load Vortex Rope as a Global Unstable Mode." ASME. J. Fluids Eng. May 2017; 139(5): 051102. https://doi.org/10.1115/1.4035640
Download citation file:
Get Email Alerts
Boundary-Layer Agitator for Advanced Convective Mixing
J. Fluids Eng (July 2024)
Passively Enhanced Vortex-Induced Vibration Response of Side-by-Side Cylinders in Turbulent Flow
J. Fluids Eng (July 2024)
Morphological Features of a Splashing Drop Extracted Using Explainable AI
J. Fluids Eng (July 2024)
Related Articles
Vortex Rope Formation in a High Head Model Francis Turbine
J. Fluids Eng (April,2017)
Proper Orthogonal Decomposition of Self-Induced Instabilities in Decelerated Swirling Flows and Their Mitigation Through Axial Water Injection
J. Fluids Eng (August,2017)
URANS Models for the Simulation of Full Load Pressure Surge in Francis Turbines Validated by Particle Image Velocimetry
J. Fluids Eng (December,2017)
Related Chapters
Cavitating Structures at Inception in Turbulent Shear Flow
Proceedings of the 10th International Symposium on Cavitation (CAV2018)
Antilock-Braking System Using Fuzzy Logic
International Conference on Mechanical and Electrical Technology, 3rd, (ICMET-China 2011), Volumes 1–3
Assessment of Flow Aggressiveness at an Ultrasonic Horn Cavitation Erosion Test Device by PVDF Pressure Measurements and 3D Flow Simulations
Proceedings of the 10th International Symposium on Cavitation (CAV2018)