Effects of pressure gradient on two-dimensional separated and reattached turbulent flows
Bibliographic record
Abstract
An experimental program is designed to study the salient features of separated and reattached flows in pressure gradients generated in asymmetric diverging and converging channels. The channels comprised a straight flat floor and a curved roof that was preceded and followed by straight parallel walls. Reference measurements were also made in a parallel-wall channel to facilitate the interpretation of the pressure gradient flows. A transverse square rib located at the start of convergence/divergence was used to create separation inside the channels. In order to simplify the interpretation of the relatively complex separated and reattached flows in the asymmetric converging and diverging channels, measurements were made in the plain converging and diverging channel without the rib on the channel wall. All the measurements were obtained using a high resolution particle image velocimetry technique. The experiments without the ribs were conducted in the diverging channel at Reynolds number based on half channel depth (Reh) of 27050 and 12450 and in the converging channel at Reh = 19280. For each of these three test conditions, a high resolution particle image velocimetry technique (PIV) was used to conduct detailed velocity measurements in the upstream parallel section, within the converging and diverging section, and downstream of the converging and diverging sections. From these measurements, the boundary layer parameters and profiles of the mean velocities, turbulent quantities as well as terms in the transport equations for turbulent kinetic energy and Reynolds stresses were obtained to document the effects of pressure gradient on the flow. In the adverse pressure gradient case, the turbulent quantities were enhanced more significantly in the lower boundary layer than the upper boundary layer. On the other hand, favorable pressure gradient attenuated the turbulence levels and the effect was found to be similar on both the upper and the lower boundary layers. For the separated and reattached flows in the converging, diverging and parallel-wall channels at Reh = 19440, 12420 and 15350, respectively. The Reynolds number based on the approach velocity and rib height was Rek 2700. From these measurements, profiles of the mean velocities, turbulent quantities and the various terms in the transport equations for turbulent kinetic energy and Reynolds stresses were also obtained. The flow dynamics in the upper boundary layer in the separated region and the early stages of flow redevelopment were observed to be insensitive to the pressure gradients. In the lower boundary layer, however, the flow dynamics were entirely dominated by the separated shear layer in the separated region as well as the early region of flow redevelopment. The effects of the separated shear layer diminished in the redevelopment region so that the dynamics of the flow were dictated by the pressure gradients. The proper orthogonal decomposition (POD) was applied to educe the dominant large scale structures in the separated and reattached flows. These dominant scales were used to document structural differences between the canonical upstream flow and the flow field within the separated and redeveloping region. The contributions of these dominant structures to the dynamics of the Reynolds normal and shear stresses are also presented and discussed. It was observed that the POD recovers Reynolds shear stress more efficiently than the turbulent kinetic energy. The reconstruction reveals that large scales contribute more to the Reynolds shear stress than the turbulent kinetic energy.
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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) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.001 |
| 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".