Numerical Investigation on Instability Flow Behaviors of Liquid Oxygen in a Feeding Pipeline with a Five-Way Spherical Cavity

The hydrodynamic information of liquid oxygen in the conveying pipeline of cryogenic launch vehicles directly determines the reliability of the operation of the turbopump. A 0.09 MPa anomalous pressure fall phenomenon in the feeding system has been observed during the flight and run test of a cryogenic rocket with four parallel engines. In previous work, we set up a full-scale experimental system with liquid oxygen as media. The anomalous pressure fall was successfully reproduced. Experimental studies of this phenomenon suggest that the problem might be associated with vortices into the five-way spherical cavity structure. The objective of this study was to determine the three-dimensional instability flow by computational methods to identify and better understand the anomalous pressure fall phenomenon. A numerical model developed by the turbulent conservation equations was validated by experimental data. The generation and evolution of vortices into the five-way spherical cavity of feeding pipelines was captured. It was found that the root cause of the instability flow causing the unusual pressure fall is the formation of a spindle-like vortex into the five-way spherical cavity due to disturbance of the inlet liquid oxygen. The results showed that there is a mirror-symmetrical four-vortices structure in the absence of disturbance, in which the liquid oxygen pressure fall with the rise of the Reynolds number is in good agreement with the predicting values calculated by a set of traditional empirical correlations. In the case of the specific operating conditions, it is also consistent with the experimental results. When the disturbance occurs at the inlet of the spherical cavity, the mirror-symmetrical four-vortices structure gradually evolves into the mirror-symmetrical two-vortices structure. When the disturbance is further enhanced, the mirror-symmetrical two-vortices structure merge with each other to form a spindle-like vortex, which is similar to the Rankine vortex structure. The pressure fall on the corresponding side of the spindle-like vortex core reduces abnormally, and is about 0.07 MPa, which is consistent with the experimental data under certain disturbance conditions. Moreover, it was found that the spindle-like vortex is a stable eddy structure, and would continue to exist once it is formed, which could also not disappear with the removal of the disturbance.