Pseudo-phase transition behaviors of supercritical CO₂ leakage flow in scallop bionic seal of turbomachinery

Sealing performance in supercritical CO₂ (SCO₂) turbomachinery is strongly influenced by pronounced variations in thermophysical properties across rotor–stator clearances, posing challenges to conventional sealing approaches. The scallop bionic seal (SBS) has been proposed to enhance leakage suppression by promoting turbulent energy dissipation. However, its performance is highly sensitive to inlet thermodynamic conditions, particularly near pseudo-critical regions. In this work, a real-gas flow solver is developed to investigate pseudo-phase transition and transcritical behaviors of SCO₂ leakage flows within SBS. The analysis focuses on the coupling between real-fluid effects, vortex evolution, and turbulence dissipation under varying inlet states. Results show that, under an identical pressure differential of 5.0 MPa, leakage flow rates vary significantly depending on inlet conditions. Specifically, under the same inlet density of ρ = 600.0 kg/m³, leakage flow rate of SBS within the supercritical pseudo-gas state (0.381 kg/s) is greater than that in the pseudo-liquid state (0.328 kg/s). When the inlet condition is in subcritical state, the leakage flow rate can be reduced to 0.119 kg/s. Pseudo-phase transition is found to substantially alter vortex structures within sealing cavities, inducing vortex splitting, interaction, and coalescence, which modulate turbulence dissipation. Transcritical behavior further leads to pronounced variations in normalized helicity and turbulence dissipation rate, thereby governing sealing performance. These findings provide physical insight into the coupled thermodynamic–fluid dynamic mechanisms of SCO₂ leakage in SBS and offer quantitative guidance for seal design and optimization under varying thermodynamic conditions.