Notice bibliographique
Résumé
Relatively few studies have been carried out on the turbulent wake structure of a finite circular cylinder and a stack partially immersed in a flat-plate turbulent boundary layer. There is a need to develop a better understanding of the wakes of these structures, since they have many important engineering applications. This thesis investigates the influence of the aspect ratio on the wake of a finite circular cylinder and the effects of the ratio of jet flow velocity to crossflow velocity (velocity ratio, R) on the wake of a stack in a cross-flow. The wake characteristics of flows over a finite circular cylinder at four different aspect ratios (AR = 3, 5, 7 and 9) were investigated experimentally at a Reynolds number of ReD = 6⨯10⁴ using two-component thermal anemometry. Each cylinder was mounted normal to a ground plane and was either completely or partially immersed in a flat-plate turbulent boundary layer. The ratio of boundary layer thickness to the cylinder diameter was 3. A similar turbulent wake structure (time-averaged velocity, turbulence intensity, and Reynolds shear stress distributions) was found for the cylinders with AR = 5, 7, and 9, while a distinctly different turbulent wake structure was found for the cylinder with AR = 3. This was consistent with the results of a previous study that focused on the time-averaged streamwise vortex structures in the wake. In addition, irrespective of the value of AR, high values were observed for the skewness and flatness factors around the free end of the cylinders, which may be attributed to the interaction of the tip vortex structures and downwash flow that dominates this region of the cylinder. The wake characteristics of a stack of aspect ratio AR = 9 were investigated using both the seven-hole pressure probe and thermal anemometry. The seven-hole probe was used to measure the three components of the time-averaged velocity field, while the thermal anemometry was used to measure two components of the turbulent velocity field at various downstream locations from the stack. The stack was mounted normal to the ground plane and was partially immersed in a flat-plate turbulent boundary layer, for which the ratio of boundary layer thickness to the stack diameter was 4.5. In addition, measurements of the vortex shedding frequency were made with a single-component hot-wire probe. The cross-flow Reynolds number was ReD = 2.3 x 10⁴, the jet Reynolds number ranged from Red = 7.6 x 10³ to 4.7 x 10⁴, and R was varied from 0 to 3. In the stack study, three flow regimes were identified depending on the value of R: the downwash (R < 0.7), cross-wind-dominated (0.7 < R < 1.5), and jet-dominated (R ≥ 1.5) flow regimes. Each flow regime had a distinct structure for the time-averaged velocity and streamwise vorticity fields, and turbulence characteristics, as well as the variation of the Strouhal number and the power spectrum of the streamwise velocity fluctuations along the stack height. The turbulence structure is complex and changes in the streamwise and wall-normal directions within the near and intermediate stack and jet wakes. In the downwash and crosswind-dominated flow regimes, two pairs of counter-rotating streamwise vortex structures were identified within the stack wake. The tip-vortex pair and base-vortex pair were similar to those found in the wake of a finite circular cylinder, located close to the free end and the base of the stack (ground plane), respectively. In the jet-dominated flow regime, a third pair of streamwise vortex structures was observed, referred to as the jet-wake vortex pair, which occurred within the jet-wake region above the free end of the stack. The jet-wake vortex pair has the same orientation as the base vortex pair and is associated with the jet rise.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,001 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,001 | 0,000 |
| Bibliométrie | 0,001 | 0,000 |
| Études des sciences et des technologies | 0,003 | 0,001 |
| Communication savante | 0,001 | 0,001 |
| Science ouverte | 0,000 | 0,002 |
| Intégrité de la recherche | 0,002 | 0,002 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,004 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».