Investigation of nozzle failure in solid rocket motor

A study has been carried out to diagnose the nozzle failure which burned through the front divergent section in middle and later stage of combustion during ground firing test of a solid rocket motor. Firstly, the derivative of radius with respect to axis of nozzle contour was analyzed, thinking that the discontinuous derivative at turning point on the contour may be the direct reason for burning through the front divergent section of nozzle. Then, comparative simulation tests showed that serious ablation occurred after the turning point for the nozzle with turning point on the contour of its divergent section, while no ablation occurred for the nozzle without turning point on the contour of its divergent section. Calculations based on the Navier-Stokes equation for prototype nozzle have proved that an eddy system exists around the turning point on the contour of divergent section, and this result coincides with the analysis on abrupt velocity change. Therefore, the reason of failure was pinpointed and proposals to improve contour design were put forward: substituting the circular arc with cosine curve to achieve continuous derivative at the turning point on the contour of divergent section, thus to alleviate rush and ablation effect and avoid burning through failure.