Conferences - Seminars

31JAN
2017
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  Tuesday 31 January 2017 14:15 - 15:15 ME D2 2423

Instability of the flow above a rotating disk

By Eunok Yim

The rotating disk is an important classical problem, due to the similarities between the 3D boundary layers on a disk and a swept aircraft wing. It is nowadays admitted that a direct transition to turbulence may exist through a steep-fronted nonlinear global mode located at the boundary between the locally connectively and absolutely unstable regions (Lingwood 1995, 1997; Pier 2003; Viaud et al. 2008, 2011; Imayama et al. 2014). However, recent studies (Healey 2010; Harris et al. 2012; Imayama et al. 2013) suggest that there may be an alternative route starting at lower critical Reynolds number, based on convective travelling waves but this scenario is still not fully validated and proven.
 
To better characterize such transition, direct numerical simulations are performed in a closed cylindrical rotor-stator cavity (without hub) up to Re~105. All boundaries are no slip and for the stable region around the rotation axis prevents the disturbances coming from the very unstable stator boundary to disturb the rotor boundary layer. Different transition scenarii to turbulence are investigated when the rotor boundary layer is forced at different positions and forcing amplitude. The associated dynamics of coherent structures in various flow regions are also investigated when increasing Re. Finally, the linear global stability of the mean-flow is investigated in order to characterize the location of the front and compare to the previous local stability analyses of a single disk.

Organization François Gallaire

Contact François Gallaire

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