Numerical Investigation of Flow Characteristics in a Supercritical Carbon Dioxide Turbine for 20 Megawatt Brayton Cycle

Efficient and clean utilization of energy has become one of the themes of sustainable development. The closed Brayton cycle with supercritical carbon dioxide(SCO₂) as working fluid has the advantages of compact structure, high efficiency and environmental friendliness, so it is widely concerned by scholars around the world. As the carrier of thermal power conversion in cycle system, the aerodynamic performance of CO₂ turbines affects the cycle efficiency crucially. However, the research work about this topic is still relatively rare in open literature. In this paper, the flow characteristics and aerodynamic performance of a SCO₂ axial-flow turbine are investigated by numerical method, and the enthalpy drop for each stage is optimized. The differences of flow characteristics under design conditions before and after optimization are compared. Finally, the off-design flow characteristics of the turbine are analyzed. The results show that compared with that before optimization, the total-to-total efficiency is increased by 0.79%, and the flow rate is increased by 4.30%. The leakage of clapboard seal and blade tip seal in the first stage is also significantly reduced. The leakage rate of the clapboard seal in the first stage reaches 3.13% of the total flow rate. The total-to-total efficiency of the turbine also decreases by 4.04% compared with that without seal clearance. In this paper, the flow characteristics of the main passage and the seal clearance of a SCO₂ turbine are deeply analyzed. The reasons for the large leakage are revealed, and the relevant factors that have a negative impact on its efficiency are summarized. The research results can provide reference for the design of SCO₂ axial flow turbines.