Numerical studies on vortex dynamics : helical vortices and two-phase vortices
We present numerical studies on the dynamics of homogeneous and two-phase vortices. In a first part, we study the structure of homogeneous helical vortices as can be found in the wake of propellers or turbines. Some properties of inviscid steady states are derived theoretically and confirmed numeric...
| Main Author: | |
|---|---|
| Other Authors: | , , , , |
| Format: | Doctoral or Postdoctoral Thesis |
| Language: | English |
| Published: |
HAL CCSD
2022
|
| Subjects: | |
| Online Access: | https://theses.hal.science/tel-03863645 https://theses.hal.science/tel-03863645/document https://theses.hal.science/tel-03863645/file/XU_Yonghui_these_2022.pdf |
| Summary: | We present numerical studies on the dynamics of homogeneous and two-phase vortices. In a first part, we study the structure of homogeneous helical vortices as can be found in the wake of propellers or turbines. Some properties of inviscid steady states are derived theoretically and confirmed numerically on quasi-equilibria using direct numerical simulations in the helical symmetry framework. Long- and short-wave instability modes growing on these states are then investigated and compared favourably to existing asymptotic theories. Axial jet intensity within the core has a prominent role, but the influence of other parameters such as helical vortex pitch and core size are also investigated. In a second part, we study two problems concerning the dynamics of two-phase vortices. On the one hand, we investigate the instabilities occurring in straight two-phase vortices using an original in-house instability code. In particular, the stabilizing effect of rotation on capillary instabilities in vortices with a gaseous core is evidenced. On the other hand, we study the generation of toroidal vortex bubbles as those produced by scuba divers, beluga whales or dolphins by direct two-phase simulations. Previous instability results are used to explain the remarkable robustness of such structures with respect to perturbations. Nous présentons des études numériques sur la dynamique des vortex homogènes et diphasiques. Dans une première partie, nous étudions la structure des vortex hélicoïdaux homogènes tels qu'on peut les trouver dans le sillage des hélices ou des turbines. Certaines propriétés des états d'équilibre non visqueux sont dérivées théoriquement et confirmées numériquement sur des états de quasi-équilibre en utilisant des simulations numériques directes dans le cadre de la symétrie hélicoïdale. Les modes d'instabilité de grandes et petites longueurs d'onde qui se développent sur ces états sont ensuite étudiés et comparés aux théories asymptotiques existantes, avec un bon accord. L'intensité du jet axial au cœur du ... |
|---|