Time-resolved topology of turbulent boundary layer separation over the trailing edge of an airfoil
Bibliographic record
Abstract
The unsteady organization of a separated turbulent boundary layer was investigated upstream from the trailing edge of a NACA 4418 airfoil. The angle of attack was in the pre-stall regime. Two particle image velocimetry fields of view were of interest: a streamwise–wall-normal plane at midspan of the airfoil and a streamwise–spanwise plane parallel to and near the surface of the airfoil. In the near-surface streamwise–spanwise plane, the mean velocity field revealed a saddle point near midspan and a pair of counter-rotating foci at the sides. This pattern is reminiscent of a stall cell, which has been traditionally associated with flow separation on thick airfoils at and slightly beyond the angle of attack of maximum lift. Isolating the low frequencies showed that the instantaneous separation front consisted of several smaller structures that also resembled a stall cell pattern, but they were an order of magnitude smaller than the one found in the mean pattern. These instantaneous stall cells were of two types: forward and backward. The forward stall cells were formed by strong high-speed streaks from upstream, while backward stall cells formed as a result of strong backflow just downstream from the separation front, resulting in a foci pair and a saddle point on their upstream side. In both cases, the foci pairs acted to mobilize high-speed momentum of the associated streak into a rotational motion, causing these streaks to dissipate. Finally, proper orthogonal decomposition revealed that low-order modes were associated with the movement and distortion of the separation front.
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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".