Numerical investigation of the flame suppression mechanism of porous muzzle brake

Hopf bifurcation, a prevalent phenomenon in solid rocket motors (SRMs), signifies a critical transition from a fixed point to a limit cycle. The detection of early warning signals (EWSs) for Hopf bifurcation is significant for preventing or mitigating potentially dangerous self-excited states. However, conventional data-driven EWSs are hindered by the lack of a consistent threshold, yielding mainly qualitative judgments when solely pre-bifurcation data are available. In this study, we introduce a transfer learning (TL) framework designed to estimate the system growth rate as an EWS utilizing pre-bifurcation data. The framework is initially trained on the correlation between dynamical features and growth rate within a source domain, generated by a reduced-order model proposed by Culick. Subsequently, it is applied to the target domain from the SRM system. This TL-based EWS exhibits remarkable sensitivity when applied to the SRM system, providing consistent threshold values for quantitative predictions based on pre-bifurcation data exclusively. Our findings present a promising path for detecting the EWSs of Hopf bifurcations in SRMs and affirm the feasibility and tremendous potential of utilizing TL in scenarios where real data are limited.

Early detection of Hopf bifurcation in a solid rocket motor via transfer learning

Xu,

Wang,

Guan

et al. 2023

Phase behavior of gas condensate in fractured-vuggy porous media based on microfluidic technology and real-time computed tomography scanning

Jing,

Zhang,

Zhang

et al. 2023

With the development of gas-condensate reservoirs, the phase behavior of gas condensate undergoes continuous changes. The phase behavior of gas condensate in PVT cylinders is different from that in fractured-vuggy gas-condensate reservoirs because multiscale pore structures can affect the phase behavior. By vuggy, we mean the formation of a reservoir contains cavity structures. To elucidate the influence of fractured-vuggy porous media on phase behavior of gas condensate, a microfluidic chip and a fractured-vuggy carbonate sample were prepared for pressure depletion experiments. The phase behavior of gas condensate in the chip during depressurization was observed via brightfield optical microscopy. The real-time computed tomography scanning was used to analyze pore structure of the sample and to obtain the phase behavior of gas condensate under different pressures. The results showed that the dew point pressure of the gas condensate was increased from 12.0 MPa in PVT cylinders to 14.8 MPa in nanochannels of the chip. The condensate liquid appeared in micropores at 14.4 MPa. The change of the average radius, coordination number, and tortuosity of condensate liquid ganglia were calculated and analyzed using pore network models. The shape factor and the Euler number were used to classify the condensate liquid into four types including clustered, branched, membranous, and droplets ganglia. The condensate liquid was generally distributed as clustered ganglia. This study provided evidence of the effect of fractured-vuggy porous media on phase behavior of gas condensate and clarified that the phase behavior of gas condensate varies in multi-scale pores.

Influence of embedded structure on two-phase reactive flow characteristics for a small combustion chamber with a moving boundary

Wang,

Zhang

2024

In special launch scenarios such as armament and aerospace, the scale of the launch system is severely restricted, which causes unstable combustion of propellant. An embedded structure for the small propulsion system driven by solid propellant is proposed to overcome this problem. This study aims to demonstrate the two-phase flow behaviors and launch safety of the combustion chamber with an embedded structure. A two-dimensional two-phase flow model based on the modified two-fluid theory is developed to describe the detailed two-phase flow behaviors in the combustion chamber during launching. Different from most of the existing studies, the constitutive equations determined from actual physical conditions are used to close the system of continuity equations. The numerical results are compared with that of the experiment to verify the accuracy of the numerical model. On this basis, the launch performance of the embedded structure is investigated. The numerical results indicate that the embedded structure facilitates the ignition process and reduces the risk of excessive pressure, but decreases the muzzle velocity at the same time. In addition, the effect of design parameters on launch safety is further investigated. Design parameters directly affect the launch safety, and the selection of reasonable parameters is a useful method for enhancing the launch performance.