How to Design a Centrifugal Compressor Stage and a Radial-Inflow Turbine Stage for a Supercritical CO2 Recompression with the Brayton Cycle?

The supercritical cycle which always operates above the critical pressure and the critical temperature of its working fluid was devised to overcome the disadvantages of Rankine cycle and recuperated Brayton cycle and retain their advantages by Feher in the 1960s.

Fig. 1. Layout of S-CO2 Recompression Brayton Cycle for a Nuclear Reactor.

It is found that the ideal gas assumption is not proper for the design of turbomachinery blades using supercritical CO2 (SCO2) as working fluid, especially near the critical point. Therefore, the inverse design method which has been successfully applied to the ideal gas is extended to applications for the real gas by using a real gas property lookup table. A fast interpolation lookup approach is implemented, which can be applied both in superheated and two-phase regimes. This method is applied to the design of a centrifugal compressor blade and a radial-inflow turbine blade for a S-CO2 recompression Brayton cycle.

The stage aerodynamic performance (volute included) of the compressor and turbine is validated numerically by using the commercial CFD code ANSYS CFX R162. The structural integrity of the designs is also confirmed by using ANSYS Workbench Mechanical R162.

Fig. 2. MC Impeller and Diffuser Flow Field near the Shroud.

In this paper, a design study of S-CO2 compressor and radial turbine used in a recompression Brayton cycle using 3D inverse design method is presented. For the first time, the real gas effect is implemented in the inverse design and is validated by comparing the blade loading (blade surface static pressure) from 3D inviscid inverse design and 3D viscous CFD simulation. The aerodynamic performance and flow field of the compressor and the turbine are investigated by CFD and their structural strength is evaluated by static structural analysis.