Introduction

The supercritical CO₂ (S-CO₂) Brayton cycle is proposed for Generation IV reactor applications because of its simplicity, high efficiency, compactness and thus potential to cost reduction. To achieve an attractive cycle efficiency (~ 45%), highly efficient cycle components must be guaranteed. Hence the turbine, the main design objective is to achieve high efficiency while maintaining the turbine at a reasonable size. Due to the high power and high mass flow rate demands of the present application an axial-flow turbine was employed. Two NASA Glenn Research Center (GRC) developed codes (TURBAN and AXOD) were modified and implemented to perform the aerodynamic design. TURBAN is a preliminary axial-flow turbine design code. AXOD is a multi-stage turbine off-design performance code. Both codes were developed for airbreathing aircraft engine and ideal gas applications. Since CO2 exhibits significantly nonideal behavior under S-CO2 cycle operating conditions, both codes were modified to apply for real gas applications. The NIST pure fluid properties database was implemented into the codes for this purpose. TURBAN-MOD and AXOD-MOD are the modified versions respectively. TURBAN-MOD determines the stage velocity diagrams, stage and overall efficiencies and simple blade geometry at a design-point. AXOD-MOD calculates the off-design performance at optimum incidence angles based on the design-point and generates characteristic maps. The off-design performance maps can be used for cycle control analysis.