This paper presents a concept of a supercritical carbon dioxide (S-CO2) bi-directional Brayton cycle energy storage system

in which the turbomachinery needs to have bi-directional operation capability. In order to study the performance characteristics of the turbomachinery under bi-directional operation conditions

this paper takes the centrifugal compressor reversing as turbine as the research object

and carries out the research through the combination of theoretical derivation and numerical calculation method. Firstly

the optimal working conditions of the compressor reverse as turbine are theoretically deduced and analyzed. Secondly

the performance characteristics of the turbine under different inlet conditions are studied by numerical simulation

and the influence law of impeller geometric parameters on the performance of the turbine is discussed. The results show that reducing the inlet temperature and increasing the inlet pressure can broaden the efficient operation range of the turbine. With the increase of flow rate

the turbine efficiency first increases and then decreases. Compared with the compressor condition

the high efficiency operating range of the turbine condition shifts to the low flow rate condition and the range narrows. The maximum efficiency under turbine condition is higher than that under compressor condition. An increase in the number of blades and blade wrap angle can boost output power and expansion ratio

yet excessive increases will lead to a decline in efficiency. The blade tip clearance has a significant effect on efficiency

and the blade wrap angle has the greatest influence on output power and expansion ratio. The research results can provide a theoretical basis and reference for the optimal design of S-CO2 centrifugal compressor as turbine and the realization of reversible compressor.