Turbulent jets in the presence of a turbulent ambient
Bibliographic record
Abstract
Turbulent mixing, which leads to dilution or chemical reactions (including combustion) at a molecular level, is studied using a passive scalar. Khorsandi (2013) and Perez-Alvarado (2016) studied the velocity and concentration fields of an axisymmetric turbulent jet in zero mean flow, respectively, in a quiescent and turbulent ambient. The aim of the present study is to extend this work observing a turbulent jet released into a nearly homogeneous isotropic turbulent background with negligible mean flow created with a random jet array. The characteristic of the jet in a turbulent background flow is compared to that released into a quiescent background. Planar laser induced fluorescence (PLIF) is used for flow visualization and to quantify concentrations in cross-sections of turbulent jets with Reynolds numbers of 5800 and 10600 at axial distances between x/D of 20 and 70. The data was post-processed using MATLAB codes. Flow visualisation shows that the jet cross-section has greater variation in position and shape when released into a turbulent ambient, due to the larger eddies of the turbulence distorting the jet path and the smaller eddies distorting the jet cross-section, until at some downstream distance the turbulence results in the breakup of the jet (zero mean jet velocity). The increased variability of the jet is seen in time traces of the centreline concentration. The jet cross-sections are spatially averaged to determine the rate of decrease of the concentration and increase of the jet half width with axial distance. Normalized centreline concentration varies with normalized axial distance as x-1 in a quiescent ambient and with x-1.7 for the jet with Re = 10600 and x-2.1 for the jet with Re = 5800 in the turbulent ambient. The normalized jet half width varies with normalized axial distance as x1 in a quiescent ambient and with x1.2 for jet Re = 10600 and x1.4 for jet Re = 5800 in the turbulent ambient. The position of the centre of mass of the jet cross-sections indicated a greater meandering of the jet path with downstream distance (Re = 10600). The radius of gyration of the jet was used to identify the growth in width of the cross-section independent of the meandering of the jet path. The normalized radius of gyration of the jet varied as x1.8 for the jet released in both quiescent and turbulent ambient, however the magnitude was greater in the turbulent ambient with a greater increase for the lower Reynolds number jet. The downstream evolution of the cross-sectional shape factor also indicated the greater disruption of the cross-section in the turbulent ambient. Lastly, the decay in the time averaged centreline concentration was compared to that of the centreline velocity and was found to decrease more gradually in the turbulent ambient. In summary, the turbulence in the ambient progressively breaks up the jet structure and distorts the jet path resulting in a faster rate of decay of the jet, which is greater for jets with lower Reynolds number.
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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 | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.002 |
| 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".