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Shock wave-boundary layer interactions in over-expanded rocket nozzles are responsible for large detached regions resulting in non-axisymetric forces called side-loads. The mechanism at stake is self-sustained and involves separation, shear layers and Mach disks. In such cases, an hybrid approach for turbulence is required. This thesis aims at investigating the potentially globally unstable nature of this unsteadiness by means of a Delayed Detached Eddy Simulations (DDES) on an over-expanded nozzle and comparing it with a fully-3D linear stability analysis. The geometry considered is a TIC nozzle, experiencing a FSS unsteadiness and operating at 3 different jet Mach number M_j=[1.83, 2.09, 2.27]. Nonlinear calculations confirm the experimental outcomes: energy in PSD spectra for wall perturbations is distributed over 2 peaks at intermediate frequency (St=0.2-0.3) and two humps at low-frequency $left(St

Shock wave-boundary layer interactions in over-expanded rocket nozzles are responsible for large detached regions resulting in non-axisymetric forces called side-loads. The mechanism at stake is self-sustained and involves separation, shear layers and Mach disks. In such cases, an hybrid approach for turbulence is required. This thesis aims at investigating the potentially globally unstable nature of this unsteadiness by means of a Delayed Detached Eddy Simulations (DDES) on an over-expanded nozzle and comparing it with a fully-3D linear stability analysis. The geometry considered is a TIC nozzle, experiencing a FSS unsteadiness and operating at 3 different jet Mach number M_j=[1.83, 2.09, 2.27]. Nonlinear calculations confirm the experimental outcomes: energy in PSD spectra for wall perturbations is distributed over 2 peaks at intermediate frequency (St=0.2-0.3) and two humps at low-frequency $left(St