This work investigates the unsteady pressure fluctuations and inception of vortical flow in a hydraulic turbine during speed-no-load conditions. At speed-no-load (SNL), the available hydraulic energy dissipates to the blades without producing an effective torque. This results in high-amplitude pressure loading and fatigue development, which take a toll on a machine's operating life. The focus of the present study is to experimentally measure and numerically characterize time-dependent pressure amplitudes in the vaneless space, runner and draft tube of a model Francis turbine. To this end, ten pressure sensors, including four miniature sensors mounted in the runner, were integrated into a turbine. The numerical model consists of the entire turbine including Labyrinth seals. Compressible flow was considered for the numerical study to account for the effect of flow compressibility and the reflection of pressure waves. The results clearly showed that the vortical flow in the blade passages induces high-amplitude stochastic fluctuations. A distinct flow pattern in the turbine runner was found. The flow near the blade suction side close to the crown was more chaotic and reversible (pumping), whereas the flow on the blade pressure side close to the band was accelerating (turbine) and directed toward the outlet. Flow separation from the blade leading edge created a vortical flow, which broke up into four parts as it traveled further downstream and created high-energy turbulent eddies. The source of reversible flow was found at the draft tube elbow, where the flow in the center core region moves toward the runner cone. The vortical region located at the inner radius of the elbow gives momentum to the wall-attached flow and is pushed toward the outlet, whereas the flow at the outer radius is pushed toward the runner. The cycle repeats at a frequency of 22.3 Hz, which is four times the runner rotational speed.
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November 2018
Research-Article
Compressible Large Eddy Simulation of a Francis Turbine During Speed-No-Load: Rotor Stator Interaction and Inception of a Vortical Flow
Chirag Trivedi
Chirag Trivedi
Mem. ASME
Waterpower Laboratory,
Faculty of Engineering,
Department of Energy and Process Engineering,
NTNU—Norwegian University of
Science and Technology,
Trondheim 7491, Norway
e-mail: chirag.trivedi@ntnu.no
Waterpower Laboratory,
Faculty of Engineering,
Department of Energy and Process Engineering,
NTNU—Norwegian University of
Science and Technology,
Trondheim 7491, Norway
e-mail: chirag.trivedi@ntnu.no
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Chirag Trivedi
Mem. ASME
Waterpower Laboratory,
Faculty of Engineering,
Department of Energy and Process Engineering,
NTNU—Norwegian University of
Science and Technology,
Trondheim 7491, Norway
e-mail: chirag.trivedi@ntnu.no
Waterpower Laboratory,
Faculty of Engineering,
Department of Energy and Process Engineering,
NTNU—Norwegian University of
Science and Technology,
Trondheim 7491, Norway
e-mail: chirag.trivedi@ntnu.no
Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 17, 2017; final manuscript received January 18, 2018; published online June 27, 2018. Assoc. Editor: Riccardo Da Soghe.
J. Eng. Gas Turbines Power. Nov 2018, 140(11): 112601 (18 pages)
Published Online: June 27, 2018
Article history
Received:
July 17, 2017
Revised:
January 18, 2018
Citation
Trivedi, C. (June 27, 2018). "Compressible Large Eddy Simulation of a Francis Turbine During Speed-No-Load: Rotor Stator Interaction and Inception of a Vortical Flow." ASME. J. Eng. Gas Turbines Power. November 2018; 140(11): 112601. https://doi.org/10.1115/1.4039423
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