Background

-Fluid structure interaction (FSI)

Hydraulic turbines include both stationary and rotating components. The interaction of the components, mainly between the runner blades and distributor vanes, is critical when the frequency of the rotor-stator interaction (RSI) approaches the runner natural frequency¹. In the recent years, several turbines have been exposed to heavy fatigue loading and development of crack in the turbine blades. The fatigue loading and the failures are associated with the hydrodynamic force and the response from the mechanical structure for the given condition. For safe and reliable design of the turbines, detailed understanding of fluid structure interaction (FSI) is essential. However, hydraulic turbine is a complex structure and extremely challenging to understand the behavior as mechanical response is dependent on the operating condition. While designing the turbine, factor of safety based on traditional design and experience is considered. However, it is not proved reliable all the time. The FSI is dependent on several parameters: (1) hydrodynamic damping, (2) nearby structure and submergence level, (3) mode-shape, (4) freestream velocity and vortex shedding, (5) damping during cavitation, (6) material properties, (7) rotational speed, (8) natural frequency of individual and combined structure, (9) flow compressibility, (10) wave propagation speed, etc.

Third Francis-99 workshop is the continuation of previous two workshops. The first workshop attempted to study the steady state operating conditions, and the second workshop attempted to study the transient operating conditions (load variation and start-stop). The third workshop will focus on FSI analysis under steady state operating conditions. Unlike the previous two workshops, the present workshop includes additional (simplified) test case of hydrofoil that allows simplified study of FSI to understand the mechanics behind the fluid structure coupling.

Acknowledgement

The experiments for the third Francis-99 workshop have been conducted under the HiFrancis project.

Scope of the workshop

Scope of the third workshop is fluid structure analysis under steady state operating conditions. More specifically, parameters such as study of mode-shape, nodal-diameter, deformation, fatigue loading, estimation of fatigue life, individual/combined natural frequencies, hydrodynamic damping, harmonic response, etc. will be investigated².

The Hydrofoil test case focuses on fluid structure analysis (one-way or two-way) and to study one/many of the above parameters. Basic/fundamental research is the main objective and how the approach (applied on hydrofoil) can be useful for the complex structure such as turbine blades. CFD analysis of the hydrofoil will be welcomed if sophisticated turbulence modeling approaches such as, detached eddy simulation, large eddy simulation (LES), hybrid RANS/LES, and direct numerical simulation (DNS), are used that will help to understand the mechanics of vortex shedding and the resonance. In addition to the harmonic response, modal analysis, acoustic model, two-way FSI is also encouraged.
The turbine test case focuses on fluid structure analysis (one-way and/or two-way) and to study one/many of the above parameters. CFD analysis in turbine is NOT the focus as it is already covered under the previous Francis-99 workshops.

Workhop committee

Disclaimer: The provided data, geometry and mesh under Francis-99 workshop series are free for research and education. Upon the usage of the data and the geometry, acknowledgement must be given. “We/I used the test-case provided by NTNU – Norwegian University of Science and Technology under the Francis-99 workshop series.”

¹Trivedi, C., Cervantes, M.J., 2017. Fluid structure interaction in hydraulic turbines: a perspective review. Renewable & Sustainable Energy Reviews 68, 87–101. https://doi.org/10.1016/j.rser.2016.09.121.