Comment on "Large-Eddy Simulation of a Turbulent Compressible Round Jet" vis-a`-vis Lighthill's Theory of Jet Noise
Bibliographic record
Abstract
HE study of Ref. 1 appears to be an advance in the use of computational e uid dynamics for the prediction of the properties of a turbulent jet. It yields details of the instantaneous e ow patterns and, in addition, two-point space-time correlations of velocity components. These components govern the sources of sound in Lighthill’ s 2 theory of jet noise (and in its extension 3 to dealwith waveconvection,hencerefraction);further,theircorrelationsarerequired in theintegralforthespectraand mean squareradiatedsound pressure.(Thisis amplie edfurtherinthefollowing.)Itappearsfrom the Abstract and presentation that the present work is motivated by these considerations in the context of Lighthill’ s theory. Although rms properties of a round jet must be axisymmetric, instantaneous values are not. These large-eddy simulation (LES) computations of the instantaneous velocity e eld show striking deviations from axisymmetry. The deviations are consistent with those found in the radiated sound e eld by Maestrello 4 in 1976. He measured electronically the correlations between the signals of a pair of microphones, say, A and B, at a e xed distance from the nozzle, separated in angle. For A and B in a plane at the nozzle normal to the axis, the correlation decayed with separation in azimuth angle to zero at 90 deg and then increased again to about 0.1 at 180 deg, that is, when A and B were on opposite sides of the jet. In other examples, correlations showed similar, but less extreme, decay as one microphone was moved away from the other along a circle of latitude. The low A:B correlations signify, of course, a marked departure from instantaneous sound e eld axisymmetry. The Lighthill theory can be extended to these two-microphone correlations as well: such an extension (involving approximation) showed general— in some cases striking— agreement with Maestrello’ s experimental curves: in broadband 5 and in narrow frequency bands. 6 The dominant feature governing all of the correlations is the difference in acoustic travel times to microphones A and B from a noncentral source eddy in the jet turbulence. In the e rst-discussed case of the last paragraph, the peculiar variation with azimuth angle is accounted for by the source directivity.
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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) | 0.000 | 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".