European High-Performance Infrastructures
in Turbulence

Inertial modes can be excited efficiently in a fluid-filled spherical shell with a differentially rotating inner sphere [1]. Previous experimental and analytic studies suggest that critical layers (i.e. corotation resonances) have a fundamental role in the excitation process [2], but so far there are no direct measurements of the shear flow exciting the inertial modes. We propose to use the Cottbus spherical shell facility to perform laser Doppler velocimetry (LDV) and Particle Image Velocimetry (PIV) measurements to study and characterize in detail the differential rotation profile of the fluid. This study is invaluable for further development and validation of the existing theoretical model involving corotation resonances. Critical layer phenomena, analogous to the one described here, play a key role in the excitation mechanism of both internal gravity waves [3] and gravito-inertial waves in stellar interiors. Moreover, for strong forcing the excited waves might transit to wave turbulence, a process not well understood for inertial waves but of great importance for geophysical flows. Thus, this study will appeal to both fluid dynamicists and stellar modelers as well.

References:

[1] Kelley, Triana, et al., Inertial waves driven by differential rotation in a planetary geometry. Geophysical and Astrophysical Fluid Dynamics, 101(5-6), 469-487 (2007)

[2] Rieutord, Triana, et al., Excitation of inertial modes in an experimental spherical-Couette flow. Physical Review E, 86, 026304 (2012)

[3] Alvan, Mathis & Decressin, The coupling between internal waves and shear-induced turbulence in stellar radiation zones: the critical layer. arXiv:1303.1715 [astro-ph.SR]