Spectral proper orthogonal decomposition of time-resolved three-dimensional flow measurements in the turbulent wake of the Ahmed body
Bibliographic record
Abstract
This study investigated the turbulent wake flow behind a flat-back Ahmed body using a combination of time-resolved tomographic particle image velocimetry measurements and spectral proper orthogonal decomposition (SPOD). The experiments were conducted at a Reynolds number of Re H = 10 000, which is defined as U ∞ H / ν , where U ∞ represents the free-stream velocity, H is the height of the body and ν represents the viscosity. The SPOD analysis revealed four distinct flow motions present in the wake of the Ahmed body, each occupying a specific range of Strouhal number, St H . Here, St H is defined as f × H / U ∞ , where f is the frequency of the motion. At the lowest resolved St H of 0.007, the system exhibited a bi-stability mode, in which the wake switched between asymmetric states consisting of a tilted toroidal vortex and a streamwise vortex. In the next St H range of 0.014 to 0.123, the flow demonstrated swinging/flapping motions, characterized by small spanwise and vertical movements of the wake barycentre. These movements were attributed to the tilting of the toroidal vortex. The third category included the vortex-shedding motions and consisted of quasi-streamwise vortices. These vortices advected in the downstream direction, causing oblique displacements of the barycentre in the streamwise-vertical plane. The peak energy of the vortex shedding was observed at St H = 0.164. Finally, shear layer instabilities induced small vertical and spanwise velocity fluctuations along the shear layers at a high St H of 1.147.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 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 source (direct Gemma or distilled Codex), 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".