Measurement of the wavenumber-frequency spectrum of wall pressure fluctuations: spiral-shaped rotative arrays with pinhole-mounted quarter inch microphones
Bibliographic record
Abstract
This paper concerns the direct measurement of wavenumber-frequency spectra beneath a two-dimensional Turbulent Boundary Layer. The main contribution of this work is the proposed setup that should help achieving a compromise between a small sensor diameter (to avoid spatial averaging) and small sensor spacing (to gain high spatial resolution). The effect of different pinhole sizes on quarter inch microphones is first studied using an acoustical coupler to perform relative calibrations. Single-point measurements of wall pressure fluctuations in a wind-tunnel confirm that a 0.5 mm pinhole quarter inch microphone correctly captures wall pressure statistics up to a frequency of 5 kHz. Under the assumption of stationnary pressure fields, it is then suggested how rotative Archimedean spirals mainly composed of pinhole microphones can provide a uniform coverage of pressure measurements on a disc, or high resolution measurements in selected directions. Using 57 of these pinhole pressure sensors, a probe microphone as a central sensor reference and 3 Knowles pressure sensor, one of the suggested designs of spiral-shaped rotative arrays was instrumented. Measurements have been performed at low Mach numbers (M < 0:1) in a closed-loop wind-tunnel, with the array flush mounted on a side of the wind tunnel. The TBL is characterized with velocity measurements, and 2D wavenumber spectra of the wall pressure fluctuations are obtained which reveal the convective peak at low frequencies. Even preliminary and still contaminated by a strong background noise, these first results indicate that the experimental setup behaves as expected but needs additional refinements. The next steps of this on-going work are finally detailed.
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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".