Large-Eddy simulation of highly under-expanded hydrogen jets using a low dissipative solver
Bibliographic record
Abstract
Large-eddy simulation (LES) of H 2 jets is carried out at nozzle pressure ratios 5.8 ≤ NPR ≤ 10. A low-dissipative, localized flux formulation is proposed and validated using 1D–3D reference cases. In the present under-expanded jet studies, the following numerical observations are made. (1) The proposed low-dissipative approach resolves both shocks and turbulence simultaneously. The transition to turbulence is noted to start up to ≈ 10 D earlier for under-expanded jets with low-dissipative approach in comparison to the fully dissipative flux approach. (2) A comparison of H 2 , CH 4 , and N 2 jets indicates a delayed transition to turbulence for H 2 at NPR = 6.5. (3) At all NPRs, the H 2 jet turbulence transition is delayed, but the transition shifts towards the nozzle when the NPR increases. (4) The normalized peak vorticity ( ω z D / U 1 ) values for Görtler vortices around the barrel shock boundary of H 2 jet is observed to be ≈ 4 times lower compared to representative CH 4 and N 2 jets. (5) For H 2 , Mach disk oscillation is observed and linked to the global POD modes at a Strouhal number range of S t ≈ 0 . 063 − 0 . 078 . • Density-based low-dissipative finite volume solver implemented within OpenFOAM®. • Shock capturing KT scheme locally activated at the location of strong shocks. • Taylor–Görtler instabilities in the near nozzle region evolved slowly in H 2 jets. • H 2 jets exhibit delayed turbulent transition in comparison to CH 4 and N 2 . • POD analysis revealed distinct frequencies associated with Mach disk oscillation in H 2 jets.
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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 | 0.000 | 0.000 |
| 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 | 0.000 |
| 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 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".