DNS of a High-Aspect-Ratio Elliptic Vortex and Its Generated Noise
Résumé
The aerodynamic evolution and the acoustic radiation of elliptic vortices with various aspect ratios are investigated by solving numerically the full compressible Navier-Stokes equations. Three behaviours are observed according to the aspect ratio σ = a/b where a and bare the major and minor semi-axes of the vortices. At the small aspect ratio σ = 1.2, the vortex rotates at a constant angular velocity and radiates like a rotating quadrupole. The acoustic radiation is in very good agreement with a reference analytical solution. At the moderate aspect ratio σ = 5, the vortex is initially unstable. However, its aspect ratio decreases due to an axisymmetrization process, which inhibites the growth of instabilities. The noise level then decreases and the radiation frequency increases. The far-tied is found to be in good agreement with the reference solution, which has been modified to take into account the evolution of the shape of the vortex. For vortices with larger aspect ratios σ ≥ 6, axisymmetrization does not occur quickly enough to stop the growth of instabilities, which splits the vortices. Then various mergings are found to occur. For instance in the case σ = 6, several successive switches between an elliptic state and a configuration of two co-rotating vortices are observed. The sound field remains weakly affected by the switches. The present results show that the initial value of the aspect ratio yields the relative weight of the axisymmetrization which stabilizes the vortex, and of the growth of instabilities which tends to split it.
Domaines
Sciences de l'ingénieur [physics]Origine | Fichiers produits par l'(les) auteur(s) |
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