Effects of free-stream turbulence intensity on transition within a laminar separation bubble
Bibliographic record
Abstract
The laminar separation bubble formed over the suction side of a NACA 0018 airfoil was studied experimentally for increasing levels of free-stream turbulence intensity. Experiments were performed in a wind tunnel facility at a chord Reynolds number of 80000 and an angle of attack of 4 degrees. The spatio-temporal flow development was characterized by means of time-resolved Particle Image Velocimetry. The results show that the height and streamwise extent of the separation bubble are reduced as the level of turbulence intensity is increased. The decrease in separation bubble length is the result of downstream and upstream shifts in the locations of mean separation and reattachment, respectively, with the later caused by an upstream shift in the location of mean transition. Velocity fluctuations in the shear layer reach significant magnitudes earlier upstream as the level of turbulence intensity is increased, leading to the upstream shift in mean transition. At the highest level of turbulence intensity investigated, significant changes occur in the flow topology and dynamics, suggesting an alteration of the transition process. Maximum spatial amplification rates of disturbances are shown to decrease as the bubble size decreases, indicating that the upstream shift in mean transition is attributed to the increase in the initial amplitude of disturbances upstream of the separation bubble. Spectra of the wall-normal velocity fluctuations show that, as the bubble size is reduced, the central frequency of disturbances remains approximately constant, but that the detectable band of unstable frequencies broadens as a result of the broader range of disturbances present in the free-stream.
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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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| 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".