Impact of semi-elliptical cracks on risk assessment for rocket nozzle structural integrity using a fluid-solid interaction

Rocket propulsion systems rely on efficient fluid dynamics within their nozzles to achieve optimal performance. However, rocket nozzles can be susceptible to various failure modes that significantly impact their performances. The aim of this study was to investigate the interaction between fluid flow and rocket nozzle structure to identify critical position prone to failure. It was performed in two steps. In the CFD section, Mach number, static pressure, wall Yplus and axial wall shear stress were predicted. In the FEA section, semi-elliptical cracks were intentionally created at the critical position where the maximum hoop stress was located, provided by the CFD analysis. To comprehensively analyze the nozzle’s failure potential, stress intensity factor was numerically carried out and Failure Assessment Diagram (FAD) was employed, as an analytical tool. Each defect depth ratio was evaluated based on its corresponding position within the assessment diagram, while considering factors such as material properties and operating conditions. The main results obtained show that the CFD analysis demonstrated good agreement with the experimental data, with a predicted separation location deviating by only 0.3%. The error between the numerical results and the local measurements on the nozzle wall is 3.84%, which is quite satisfactory. Additionally, the failure assessment indicated that crack depth ratios (a/t > 0.5) in the critical position of the nozzle lead to failure, while ratios (a/t < 0.5) remain within the safe region.