• free separation shock [FSS]
• shock patterns
• fast Fourier transform [FFT]
• over-expanded nozzle
• fluid-structure interaction [FSI]
• start-up
• transient analysis
• side load
• finite element analysis [FEA]
• computational fluid dynamics [CFD]
• dynamic structural analysis
• boundary layer [BL]
• Vulcain II
• supersonic flow
• turbulent Interaction
• shock patterns
• restricted separation shock [RSS]
• FSS/RSS hysteresis

Overexpanded thrust-optimized contour “TOC” nozzles are suffering from significant side-load oscillations while operating at low exit pressure. This condition happens during start-up, shut-down and low-altitude atmospheric flight. All launch vehicle nozzles’ life and integrity are being affected by side-loads because These loads cause structure-degradation which affects performance and sometimes lead to severe structural damage, subsequently, a total loss of the launcher. The development in this topic is to a large extent motivated by the raised demand for high-performance nozzles in the rockets industry. For seeking a high-performance nozzle, the expansion ratio has to be as high as possible to ensure better conversion of the internally released energy from the combustion process into kinetic energy at the exit of the nozzle, however having a high expansion ratio increases the weight of the nozzle so that design-compromise must be studied with care. This thesis provides a fluid-structure interaction “FSI” investigation during the Vulcain II start-up phase. 1-way and 2-way transient FSI analysis had been implemented based on collected research data that were found for the start-up combustion pressure profiles and inlet time variant conditions of the Vulcain II. The implemented procedure correctly captured the oscillations of the side load which are generated due to the separation patterns and its highly transient transition between the captured free shock separation “FSS” and restricted shock separation “RSS”. Results showed a good agreement with a real start-up test record.