The limit to drag reduction by elastic reconfiguration due to dynamicalinstability
Bibliographic record
Abstract
Flexible structures in nature, namely plants, can have large deformations when they are subjected to wind and can cause various problems that have an impact on society and economy. For example, windthrow can lead to damage to houses or electrical installation destruction. Plants are flexible and bend with the flow which leads to a drag reduction, this structure's deformation and change of shape is called reconfiguration. Here we consider a flexible, thin, rectangular plate clamped in the middle and set normal to an airflow, as an idealized representation of plants. The flexibility of the structure is considered as an advantage at moderate flow speed because it allows reconfiguration and drag reduction, but it can also be at the origin of several flow-induced vibration phenomena at higher flow speeds. An experimental wind tunnel campaign is proposed in this study to define the limitation to elastic reconfiguration that dynamic instability imposes. Here we show by increasing the flow speed that the flexibility permits a considerable reduction of drag by reconfiguration, compared to the rigid case. However, beyond the stability limit, vibrations occur and limit the reconfiguration. This limit is represented by two dimensionless numbers: the mass number defined as the ratio between the mass of the solid and the fluid, and the Cauchy number written as the ratio of the aerodynamic load to the stiffness of the structure. Our results reveal the existence of a Critical Cauchy number below which static reconfiguration with drag reduction is possible and above which a dynamic instability with fluctuating loads is present. This critical Cauchy number is dependent on the mass number. Therefore, we examine a trend between the flexibility and the critical Cauchy number, relevant to identify an optimal flexibility for the structure that leads to a drag reduction by reconfiguration while avoiding dynamic instability. These results will be a starting point to understand the impact of reconfiguration on the occurrence of instability phenomena in the flexible structure's wake and to identify the type of vibrations that appear. Because the system we consider is bluff yet aligned with the flow, it is unclear whether the vibrations are due to a flutter instability or vortex-induced vibration.
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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 | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".