Theoretical supercritical fluid dynamics and mixing revealed in study on liquid rocket engines

Under certain pressure and temperature conditions, a material can exist in a supercritical fluidic state, where it exhibits both gas and liquid properties. This state has garnered recent attention for reaction engines that require higher pressure differences for more efficient operation, such as that described by the Brayton cycle of a constant pressure heat engine. Systems involving supercritical fluids, however, operate at extreme conditions and exhibit complex behaviors, requiring more in-depth explorations into the system dynamics to drive toward better optimization.

Research published in Physics of Fluids numerically details, for the first time, the flow structures and mixing dynamics under supercritical conditions for oxygen-rich, staged-combustion cycle engine operations. The nonlinear nature arising from the fluid compressibility and inertial variability complicates the behavior of these engine systems under supercritical conditions. The authors also considered effects of the system geometry for further optimization.

Calculations of the flow structures and fluid mixing showed that the recess length of the injector plays a critical role in the flow evolution characteristics. The recess length changed the flow type through the role of a fuel shield. The injector structure was shown to affect the vortex creation in kerosene/oxygen shear layer, which varies the mixing dynamics and, thus, the engine efficiency. Flow instabilities were caused primarily from unstable fluid injection and mixing.

According to the authors, they are the first to develop an integrated theoretical/numerical framework required for systemic studies of these supercritical fluid flows. The present work combines physics exploration with state-of-the-art parallel programming and data analytics, giving it the potential to impact a variety of fields involving supercritical fluids beyond reaction engines.

Source: “Supercritical fluid flow dynamics and mixing in gas-centered liquid-swirl coaxial injectors,” by Liwei Zhang, Xingjian Wang, Yixing Li, Shiang-Ting Yeh, and Vigor Yang, Phys. of Fluids (2018). The article can be accessed at https://doi.org/10.1063/1.5026786 .