Fig.1

Hundred-kilowatt-class CO2 energy storage system (a) and its turbine expander (b)"

Table 1

Design parameters of CO2 turbine"

Table 2

Main design results of CO2 turbine"

Fig.2

Verification of grid-independence"

Fig.3

Nozzle and impeller grid"

Table 3

Comparison of design results and simulation results"

Fig. 4

Flow field distribution inside the turbine"

Fig. 5

Impeller top clearance leakage flow"

Fig. 6

Distribution of static temperature (a) and static pressure (b) in the turbine under design conditions"

Fig. 7

Static pressure distribution at different blade heights for nozzle (a) and impeller (b)"

Fig. 8

Effect of inlet pressure on turbine performance"

Table 4

Effect of Inlet Pressure on Volumetric Flow Rate"

Fig. 9

Schematic diagram of impeller inlet angle, impeller outlet angle (a) and impller top clearance (b)"

Fig. 10

Relative Mach number distribution of the turbine with different number of blades"

Fig. 11

Effect of different impeller inlet angles on turbine performance"

Fig. 12

Turbine streamline distribution for different impeller inlet angles"

Table 5

Comparison of turbine performance under different impeller outlet angles"

Fig. 13

Turbine streamline at 20% blade height"

Fig. 14

Turbine streamline at 50% blade height"

Fig. 15

Turbine streamline at 80% blade height"

Fig. 16

Comparison of CO2 centripetal turbine efficiency before and after optimization"

Fig. 17

Effect of impeller top clearance on turbine performance"

Fig. 18

Streamline distribution of cross section with different impeller top clearances"

Fig. 19

Streamline distribution inside the impeller with different top clearances"

Table 6

Comparison between NLH simulation and steady simulation"

Fig. 20

Distribution of entropy at different moments of NLH simulation"

Table 7

Comparison between full three-dimensional viscous unsteady, NLH methodand steady simulation"

Fig. 21

Distribution of entropy at different moments of the full three-dimensional viscous unsteady simulation"