A semi-analytical model for Mach reflection in axisymmetric steady overexpanded jets
Bibliographic record
Abstract
A semi-analytical model for solving Mach reflection in axisymmetric overexpanded jets, just downstream from the exit of a nozzle, is developed.The flow considered is a steady, inviscid flow of an ideal gas.The model consists of incident and reflected flowfields solved using the method of characteristics and a Mach stream flowfield solved by quasi-one-dimensional relations.When certain cases occur, the model is able to produce additional flowfields.These are calculated to either refine the calculations around the axis of symmetry for small Mach stems, or to model the expansion fan and its interaction with the Mach stream.The results for Mach disk radius are compared with the inviscid numerical simulations using an in-house adaptive unstructured finite-volume flow solver.Two methods are detailed and applied to verify assumptions used in the model.Furthermore, the model is also compared to CFD simulations and experimental data found in the literature.Special attention is given to the cases with small Mach disks which are difficult to resolve in experiments with optical flow visualization.The high computational efficiency of the model allows for parametric studies to be performed on various aspects of the jet flow.The impact of nozzle pressure ratio and exit Mach number is analyzed in relation to the Mach stem height, jet boundary, and Mach stream.The limitations and influences of the expansion fan interaction with the Mach stream are then investigated.Comparison with experimental data is made where applicable.To begin, I would like to express my sincere gratitude to Professor Evgeny Timofeev, whose support has been constant throughout this research endeavor.His continuous guidance and mentorship have been crucial to the completion of this research.My appreciation also goes out to Ben Shoesmith for his generous availability and assistance with the MATLAB code, a contribution that significantly enhanced the technical aspects of the study, as well as the invaluable discussions on the subject.I would like to also thank Rabi Tahir and his expertise in providing timely
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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) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
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".