Curvature-driven energy distribution and vortex-entropy coupling characteristics of jet fuel in curved pipes

Heated, curved pipes are critical components for fluid transport and heat transfer in fields such as nuclear energy, thermal power, and aerospace. Complex vortex structures and multi-field coupling can lead to deteriorated heat transfer and energy loss. This study focused on a heated U-bend by combining third-generation vortex identification methods, entropy generation, and correlation analyses to systematically investigate the mechanisms of energy transmission, transformation, and redistribution in curved pipes. Centrifugal forces led to a Dean vortex and flow separation in the curved section, which began to emerge at bending angles of 60°–70° and fully developed at 80°–90°. Under the combined influence of mainstream and secondary flows, energy was redistributed, and part of the kinetic energy was transformed into turbulent pulsation, vortex, or thermal energy, thereby generating irreversible entropy generation. Increasing the flow rate enhanced the conversion of the flow kinetic energy into turbulent dissipation. When the heat flux density increased from 0.25q0 to 1.5q0, the thermal entropy generation increased 5.38 times. Higher flow rates were conducive to dominant shear enstrophy, whereas increased heat flux suppressed shear motion and strengthened the rotational characteristics of the flow. The shear effect exhibited stronger correlations with different entropy generation. At high flow rates, the correlation coefficient between the shear vorticity transport intensity and direct entropy generation increased from 0.17 to 0.72. Overall, this study reveals the coupled mechanisms among vortex structures and energy dissipation, identifying the core inducement of irreversible energy loss. This study provides theoretical support for optimizing pipe design.