Experimental Investigation of the Periodic Unsteady Transonic Flow Field Around a Compressor Blade by Means of Particle Image Velocimetry (PIV)
Bibliographic record
Abstract
In the present article, a study of the time‐dependent transonic flow field around an isolated airfoil in a Laval nozzle is presented. In order to obtain instantaneous flow field information all over the flow around the blade, the Particle Image Velocimetry (PIV) method has been employed allowing one to obtain velocity data in an illuminated light sheet with a high data acquisition rate and high spatial resolution. From these instantaneous PIV measurements the mean velocity field and turbulence quantities of the flow easily can be obtained by statistical means. A single compressor blade with a NACA 3506 profile and a chord length of 78 mm is centrally mounted in the test section. A vibration system driven by a hydraulic motor is externally attached to the blade. The rotational motion of the motor is translated to a plunging blade vibration perpendicular to the chord via an eccentric shaft and connecting arm. The vibration frequency can be varied between 0 and 100 Hz, and the average amplitude is approximately 0.4 mm. The entire blade‐motor assembly is mounted to the tunnel sidewall via a circular disc to allow easy adjustment of the inlet flow incidence angle. The exit pressure of the nozzle can be varied by a rotating flat plate (15 mm high, 39 mm wide, and 2 mm thick) that is mounted approximately 5 times the chord length downstream of the blade mid‐chord. The rotational frequency of this assembly can be varied between 0 and 100 Hz, producing upstream‐running waves at the doubled frequency (i.e., 0 to 200 Hz). The above excitation systems can be precisely synchronized and the phase lag between them can be freely varied. This allows for unsteady measurements to be conducted in the presence of only the downstream perturbation, only the blade vibration, or a combination of the two for different phase angles. For the first test series the existing PIV measurement system at Turbomachinery Institute (LTT) has been applied to measure the transonic steady flow field around the compressor blade. In another test series, measurements of the time‐dependent periodic flow field were conducted by means of PIV. This measurement series consisted of three subtasks: the measurement of the unsteady flow field with only back pressure variation, with only blade vibration, and finally with a combination of both back pressure variation and blade vibration. These results quantify not only the unsteady motion of the normal shock for each case on the suction side of the blade, but also give a detailed insight into the instantaneous transonic flow field around the compressor blade. Furthermore, the results of the set of unsteady measurements with both back pressure variation and blade vibration (3) is compared with the combination of the results of the sets of unsteady measurements of only back pressure variation (1) and only blade vibration (2) to validate the superposition principle. Finally, phase averaging of the instantaneous flowquantities produced a large database for statistical treatment (e.g., turbulence) and thus the ability to compare the averaged results with those from traditional measurement techniques.
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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) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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 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".