Study of the similarity laws for supercritical CO2 turbine performance testing using high pressurized air

Closed regenerative Brayton cycle utilizing supercritical CO2 as working fluid has attracted more concern recently as it offers high cycle thermal efficiency and decreases size of turbomachinery. The performance testing of the CO2 turbine is very important for the supercritical CO2 cycle development. However, testing the turbine performance in a closed supercritical CO2 cycle is of difficulty and complication. This paper proposes a novel experimental method on CO2 turbine testing using high pressurized air as surrogate fluid. The performance similarity laws for the experimental method are studied, because traditional similarity criteria are not applicable since supercritical CO2 and high pressurized air are both non-ideal gases. A CO2 turbine is simulated by the CFD method under similar operating conditions with CO2 and high pressurized air, and turbine performance and flow field is analyzed. CFD analysis results show that turbine's overall performance matches up well, and difference of parameter in flow field is small. The proposed experimental method can be used for CO2 turbine performance testing without setting up the complex closed supercritical CO2 cycle test bench.