Experimental investigation of nozzle geometry effect on the characteristics and structure of submerged twin jets
Bibliographic record
Abstract
The effects of nozzle geometry on the mean and turbulent characteristics of submerged twin jets were experimentally investigated. The experiments were conducted at fixed Reynolds number and offset height ratio of 4,400 and h⁄d=2, respectively. The jets were produced from three nozzle geometries: round, square, and rectangle, with the rectangular nozzle geometry oriented in the minor (rect_min) and major (rect_maj) planes. The twin nozzles of each geometry type were aligned parallel to the free surface, and the separation ratio between the twin jets was fixed at G⁄d=2.3 for all cases. Velocity measurements were obtained using a particle image velocimetry (PIV) technique, and analyses of various quantities such as the instantaneous, mean, and surface velocities, as well as the turbulent statistics were performed. The jet-free surface interaction was examined using mean and turbulent surface velocities at the free surface, velocity defect, and vorticity thickness. Two-point velocity correlation and joint probability density function revealed the dynamics of the turbulent structures. Results from the velocity contours showed that the shear layer expansion was most rapid in twin jets produced from the rect_min nozzle geometry, which resulted in the shortest attachment length to the free surface. The instantaneous velocity field showed the most prograde and retrograde vortices in the rect_min nozzle geometry, accounting for the fastest shear layer expansion. Surface-normal profiles of the Reynolds stress ratio showed an enhancement of about 60% at the free surface and that the Townsend structure parameter was dependent on nozzle geometry. The mean surface velocity revealed that the free surface was in a state of strain due to alternating velocity gradient and was most intense in the rect_min jet. Large-scale structures produced along the centreline of the jet father away from the free surface (jet B) showed a larger streamwise extent compared to those along the centreline of the jet closer to the free surface (jet A) and were independent of nozzle geometry. Analysis of the joint probability density function of the streamwise and surface-normal velocity fluctuations showed that within the shear layer, the Reynolds shear stress producing events were dominated by slow entrainment and fast ejection events, and the damping effect of the free surface was least on the rect_min jets.
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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 | 0.001 | 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 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| 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".