Physical Mechanisms Leading to Large Unsteady Pressure Fluctuations in a Gas Turbine Testing Facility
Bibliographic record
Abstract
Abstract This paper is a detailed computational study of the flow within a scale model of a gas turbine engine testing facility. At mass flows representative of tests for large, high bypass ratio turbofans, large amplitude low-frequency pressure fluctuations have been observed experimentally at full- and model-scale. These can be so large as to have deleterious effects on downstream facility components. Improved, delayed, detached eddy simulations (IDDES) of the scale model facility are carried out two operating points using OpenFOAM: one where the high amplitude fluctuations occur, and another where they do not. By comparing detailed assessments of the unsteady flow fields for both conditions, the underlying physical mechanism responsible for the problematic pressure fluctuations is identified. The first key finding is that the shape of the chamber housing the engine being tested can result in excitation of a cut-on mode leading to high-pressure amplitudes and propagation. The second key outcome is that the shear layer shedding frequency will only lead to high amplitudes of pressure fluctuation if the excited mode causes periods of high/low pressure that are synchronized around the circular shear layer. An analytical model is derived for predicting whether tonal propagation occurs. Finally, it is found that far downstream flow behavior is mostly determined by the excitation in the test chamber, with minimal downstream dissipation.
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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 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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".