Vortex Evolution and Turbulence Dissipation During Leakage Flow in the Scallop Bionic Seal of Supercritical CO2 Turbomachinery Unit

Abstract

Abstract. The supercritical carbon dioxide (SCO2) Brayton cycle system is considered one of the most representative energy conversion systems of the future. Current seal solutions used in the SCO2 turbomachinery have difficulties in suppressing leakage of SCO2 with variable thermophysical properties in the gap between the rotor and the stator. The scallop bionic seal (SBS) is an innovative sealing solution for the SCO2 turbomachinery. The bionic cavities of the SBS promote vortex development and turbulence dissipation in the SCO2 leakage flow, improving the SBS’s sealing performance. However, the transient turbulence dissipation of the leakage flow inside the SBS subjected to rotor shear makes the experimental result deviate from its design objective. This research developed a high-order flow solver to analyze the transient behaviors of leakage flow inside SBS. The mechanism of vortex development on leakage flow turbulence dissipation is elucidated, and a novel correlation between the variation frequency in turbulence dissipation and the rotor’s rotational frequency is discovered. The results indicate that the spatial development of vortices under the rotor’s shearing action is the primary factor affecting turbulent dissipation. The helicity of leakage flow suggests that the vortices undergo merging, splitting, and shedding processes. There is a correlation between the change frequency in the leakage flow turbulent dissipation and the rotor rotation frequency, resulting in the frequency of periodic changes in the leakage rate of SBS being one-half of the rotor rotation frequency. This study supports the application of the SBS operating in the SCO2 turbomachinery unit.