A huge amount of energy is stored in the spin and orbital motions of any planet. Harmonic forcings such as libration, precession and tides are capable of conveying a portion of this energy to drive intense three-dimensional flows in liquid layers of planetary bodies. The generated flows remain largely unknown even if they are important to constraint model of planetary interior or to explain the presence of magnetic fields in some astrophysical bodies. In this thesis, we study the mechanisms induced by these forcings by combining theoretical, experimental and numerical approaches and we highlight the genericity of the observed phenomena. The study of a longitudinal libration forcing, corresponding to os- cillations of the rotation rate of a planet, shows the presence of a mean zonal flow generated by non-linear interactions in the viscous layers. We then study the instability which appears at the outer boundary at sufficiently large libration amplitude or small Ekman number and which can transfer energy to the bulk of the fluid. Finally, an experimental study of tidal forcing in a sphere shows that the nonlinear self-interaction of excited iner- tial waves may drive an intense and localised axisymmetric jet, which becomes unstable at low Ekman number following a shear instability, generating space-filling turbulence. To conclude, we consider the relevance of these results to geo-/astrophysical applica- tions, such as the subsurface oceans of the icy satellites Ganymede, Enceladus or Europa.
