Experimental study of the flow of the Tr-Francis turbine along the no-load curve
Bibliographic record
Abstract
Abstract Emergence of new renewable energies, such as solar or wind power, has introduced intermittency on the grid. Hydraulic turbines, initially designed to perform close to their best efficiency point, are more and more at off-design operating conditions, such as no-load regimes, when the runner rotates without energy extraction. These no-load regimes are characterized by complex flow phenomena inducing fluctuations of the blade loading and resulting in a reduced lifetime of the runner. Understanding the origins of pressure fluctuations in no-load conditions is consequently essential to prevent fatigue damage to the turbine. This paper presents the study, with experimental flow visualization, pressure measurements and numerical simulations, of the flow behavior at speed no-load in a medium head Francis turbine model. Evolution of the different flow structures along the no-load curve is then assessed. At speed-no-load, flow visualizations show the presence of a cavitating zone at the blade trailing edge. According to the results of the numerical simulations, this zone seems to correspond to the region where a backflow in the draft tube enters the runner. This interaction results in a backflow inside the runner and in a blockage of the upper part of the inter-blade channel. Sensitivity of this cavitating region to test parameters (discharge and rotation speed) is investigated for different no-load operating points with high-speed visualization at a constant cavitation number. Decrease of the energy coefficient tends to intensify the phenomena and increase the volume of cavitation.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".