Flow prediction model for multi-stage labyrinth regulating valve based on supercritical CO2 energy dissipation mechanism

The multi-stage labyrinth regulating valve is capable of regulating the thermodynamic properties of the working medium at the inlet of the turbomachinery bypass system. However, the thermophysical properties of supercritical carbon dioxide (S-CO2) exhibit drastic nonlinear variations with pressure near the critical point, making the fluid energy dissipation process in the compressor inlet of the supercritical carbon dioxide Brayton cycle highly complex. It leads to inaccuracies in predicting the flow rate, causing deviations from the design operating conditions and potentially resulting in stall and surge. To address this gap, this study numerically investigated the fluid dynamics and energy loss mechanisms of S-CO2 with various channel geometric features, including decompression stages (n), expansion coefficient (γ), swing amplitude (w∗), channel spacing (λ∗), and aspect ratio (σ). The results indicate that n has the most significant impact on the decompression performance and flow velocity control. Only when the decompression stages are designed reasonably can the fluid velocity be effectively controlled. According to entropy production analysis, the primary mechanism of energy loss within labyrinth channels is viscous dissipation. The kinetic energy dissipated by viscous friction mainly occurs in three key regions: the boundary layer separation zone between the mainstream and low-speed vortices, the area of direct fluid impact on the wall, and the region of high-speed converging vortices. Finally, a flow prediction model is developed based on the inherent correlation between channel geometric features and Fluid energy dissipation behavior, with a prediction error of less than ±15%.