Spectral energy cascade of body rotations and oscillations under turbulence.

The rotation of rigid bodies and oscillation of flexible structures under turbulence are described and characterized in the spectral domain. Laboratory experiments combined with theory are used to unravel and explain the characteristic power-law decay of the spectrum of rotation and oscillation of simple structures. It is shown that the energy-containing eddies and inertial subrange of the incoming velocity spectrum strongly modulate the unsteady motions of structures. The spectra of the rotation and oscillation of the structures exhibit distinctive power-law decays f^{+2} and f^{-5/3-2} in the comparatively low- and high-frequency regions. The range of these regions depends on the phenomenon triggering the motions, i.e., thrust or vortex-induced motions.