Favorable pressure gradient turbulent flow over straight and inclined ribs on both channel walls
Bibliographic record
Abstract
This paper reports on experimental study of turbulent flows over straight and inclined transverse ribs of square and triangular cross sections attached to the bottom and top walls of an asymmetric converging channel. The pitch-to-height ratio of the ribs was 10. A particle image velocimetry technique was used to conduct extensive velocity measurements at channel midspan and in planes close to the leading and trailing edges of the inclined ribs. From these measurements, spatial averaged profiles of the mean velocity and higher order statistics were obtained to study the effects of rib geometry, pressure gradient, spanwise plane, and rib inclination on the flow characteristics. The results show that rib geometry has no significant effects on the mean flow and turbulent quantities. The roughness effects produced by the straight ribs outweighed pressure gradient effects in the inner region of the flow. As a result, the skin friction coefficient is nearly independent of pressure gradient. The Reynolds shear stress and turbulent transport of the shear stress are also independent of pressure gradient. On the contrary, favorable pressure gradient decreased the Reynolds normal stresses in the outer region and increased the magnitudes of the triple velocity correlations and transport of turbulent kinetic energy (TKE). The three-dimensional secondary motion produced by the inclined ribs distorted the mean flow pattern and substantially diminished the ribs’ effectiveness to augment skin friction and turbulence. For example, the skin friction over the inclined ribs is only 50%–70% of the value measured over the straight ribs. Furthermore, the size of equivalent sand grain required to produce the same amount of drag is one-tenth to one-third of the rib height for the inclined ribs compared to two- to fourfold for the straight ribs. The inclined ribs also reduced the level of the Reynolds stresses, triple velocity correlations, and transport of both the turbulent kinetic energy and Reynolds shear stress compared to the straight ribs. The skewness factors showed that important structural differences exist between flows over straight and inclined ribs.
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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 | 0.001 |
| 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 | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".