Large scale dynamics in a turbulent compressible rotor/stator cavity flow at high Reynolds number
Résumé
This paper reports an experimental investigation of a turbulent flow confined within a rotor/stator cavity of aspect ratio close to unity at high Reynolds number. The experiments have been driven by changing both the rotation rate of the disk and the thermodynamical properties of the working fluid. This fluid is sulfur hexafluoride (SF 6) whose physical properties are adjusted by imposing the operating temperature and the absolute pressure in the pressurized vessel, especially near the critical point of SF 6 reached for T c = 45.58 • C, P c = 37.55 bar. This original setup allows to obtain Reynolds numbers as high as 2 10 7 together with compressibility effects as the Mach number can reach 0.5. Pressure measurements reveal that the resulting fully turbulent flow shows both a direct and an inverse cascade as observed in rotating turbulence and in accordance with Kraichnan conjecture for 2D-turbulence. The spectra are however dominated by low-frequency peaks, which are subharmonics of the rotating disk frequency, involving large scale structures at small azimuthal wavenumbers. These modes appear for a Reynolds number around 10 5 and experience a transition at a critical Reynolds number Re c ≈ 10 6. Moreover they show an unexpected non linear behavior that we understand with the help of a low dimensional amplitude equations.
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