Study on similitude method for turbine considering working fluid physical properties variation

New turbines using S-CO₂, organic matter, inert gas, and other working fluids have gradually become an important study field and are often used for clean energy generation. Turbine operating characteristics under working conditions can be obtained using similitude methods during air turbine tests at low temperatures. However, most of the existing similitude methods do not consider changes in the physical properties of the working fluid. Through theoretical analysis and numerical verification, the similarity criterion when the physical properties of the working fluid remain unchanged cannot guarantee the flow field similarity when the physical properties change. In this paper, a similitude method for turbine considering the physical properties of the working fluid is proposed. This method ensures the similarity of the flow field by ensuring that the Reynolds number, reduced speed, and reduced isentropic work are equal under different working conditions. The numerical simulation results show that this method can ensure similarities of turbine efficiency and ensure similarity of flow field approximately under various working conditions. When the physical properties of the working fluid change due to changes in the working fluid temperature, this method can still guarantee the similarity. In addition, this method can be applied to axial and radial turbines.