  We report an experimental study of the decay of grid-generated turbulence in
a confined geometry submitted to a global rotation. Turbulence is generated by
rapidly towing a grid in a parallelepipedic water tank. The velocity fields of
a large number of independent decays are measured in a vertical plane parallel
to the rotation axis using a corotating Particle Image Velocimetry system. We
first show that, when a "simple" grid is used, a significant amount of the
kinetic energy (typically 50%) is stored in a reproducible flow composed of
resonant inertial modes. The spatial structure of those inertial modes,
extracted by band-pass filtering, is found compatible with the numerical
results of Maas [Fluid Dyn. Res. 33, 373 (2003)]. The possible coupling between
these modes and turbulence suggests that turbulence cannot be considered as
freely decaying in this configuration. Finally, we demonstrate that these
inertial modes may be significantly reduced (down to 15% of the total energy)
by adding a set of inner tanks attached to the grid. This suggests that it is
possible to produce an effectively freely decaying rotating turbulence in a
confined geometry.
