| Autor: |
Rolandi, Laura Victoria, Fontane, Jérôme, Gressier, Jérémie, Jardin, Thierry, Joly, Laurent |
| Přispěvatelé: |
Institut Supérieur de l'Aéronautique et de l'Espace - ISAE-SUPAERO (FRANCE) |
| Jazyk: |
angličtina |
| Rok vydání: |
2022 |
| Předmět: |
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| Popis: |
With a growing interest in low Reynolds numbers compressible flows, the aim of this work is to investigate compressibility effects on the wake dynamics of the circular cylinder. In particular, our focus is made on the so called Mode A and Mode B secondary instabilities, which are responsible of the transition from a two-dimensional periodic to a three-dimensional state. Mode A appears at Re=180−190 and is associated with an elliptic instability of the primary vortex cores with large scale transverse structures at a spanwise wavelength of λz~4D, where D indicates the cylinder diameter. Mode B, which arises at Re=230−260, is instead associated with a hyperbolic instability developing in the braid region and is related to the formation of finer scale structures of characteristic wavelength λz~1D. We address the influence of compressibility on these modes. The analysis has been conducted for Reynolds numbers Re in [200; 350] and Mach numbers up to M=0.5. The two-dimensional periodic base state is found to exhibit time-averaged properties that substantially vary within the range of Reynolds and Mach numbers considered. Specifically, three different types of time-averaged flow structure are identified when varying both Reynolds and Mach numbers for three representative cases. The two-dimensional periodic flow is used as base state for a global stability analysis performed by means of Floquet theory. The global modal stability solver is based on the Krylov–Schur algorithm with a time-stepping approach. A stabilizing (decreasing Floquet multiplier μ) or a destabilizing (increasing μ) effect of compressibility is observed on Mode A depending on the Reynolds number and the mode wavelength, while Mode B is found to be stabilized by compressibility. Interestingly, the characteristic length-scales of the time-averaged base flow recirculation region are found to be relevant for the normalisation of the instability wavelengths λz. The Mach number increase is also found to promote vorticity anisotropy on Mode A at largest wavelengths, which is not instead observed for Mode B. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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