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This paper presents a comprehensive study on the stagnation properties namely the total pressure and total temperature for supercritical CO2 flows including the methodology, applications and detailed analysis. Due to the high nonlinear real gas effect, it is practically impossible to have explicit expressions between static and its corresponding stagnation properties. The equations of obtaining the real gas stagnation properties as well as their physical meanings related to fluid dynamics need to be reconsidered. In this paper, the stagnation pressure and temperature for sCO2 flows are accurately calculated in a way that implicitly iterated from stagnation enthalpy and entropy without any addendum assumptions. Accordingly, this approach is applied to typical applications that essentially exert stagnation properties. The total pressure and total temperature of typical sCO2 flows in which contain significant real gas characteristics are numerically studied by using our in-house CFD code coupled with real gas models. It is found that the real gas tends to preserve more internal energy than the ideal gas during irreversible flow process especially with the presence of shockwaves. Finally, as a regular indicator of viscous flow loss, the total pressure loss for a sCO2 compressor cascade is evaluated. NOMENCLATURE U Velocity in x-direction m/s V Velocity in y-direction m/s W Velocity in z-direction m/s T Static temperate K P Static pressure Pa h Static enthalpy J kg−1 K−1 s Static entropy J kg−1 K−1 u Magnitude of flow velocity m/s ρ Density Kg/m3 Tc Critical temperature 304.13K Pc Critical pressure 7.3773MPa Non-dimensional parameters Z Compression factor ns Isentropic exponent[6] T v p s v P c c P v n          ms Isentropic exponent[6] s s v p p v m           Symbols t Stagnation condition s Static condition 1 Inflow measurement station 2 Outflow measurement station INTRODUCTION The merit of using supercritical CO2 (sCO2) as the working fluid of closed Brayton Cycle gas turbine is now widely recognized as it offers alternatives for solar, geo-thermal, and nuclear energy conversion. This technique relies on the reduced compression work of the working fluid performing close to the critical point while maintains a compact configuration compared with conventional cycles [1] which results in a strong real gas effect difficulties to be analyzed. The stagnation quantities (i.e. total properties) are the sum of the static and dynamic properties of flow, which are essential throughout the whole design, testing and simulating processes. They maintain important physical meanings in terms of fluid dynamics, namely an effective measure of total head of the flow. The first example could be the sCO2 compressor aerodynamic performance, in which the compression ratio is characterized by the total pressure ratio. The deviation on corrected mass flow or total pressure ratio will possibly degrade the whole design. The second example is the Pitot probe, which provides flow velocity from the measured total and static pressures. The third example appears in CFD solvers. Imposing the total temperature and total pressure as the inlet boundary conditions is a common practice in most turbomachinery simulation, yet it becomes non-trivial in real gas simulation as opposed to ideal gas cases because the static pressure and temperature cannot be specified explicitly. The fourth typical example could be the flow loss evaluation by total pressure during the turbomachinery aerodynamic design or analysis. Design methods or loss models need to be modified on a basis of real gas concept in case of misleading in design. Thus, there has been significant interest in understanding the real gas stagnation properties. However, the total-to-static relationships acquired for ideal gas cannot be directly applied to sCO2 flows due to the presence of real gas effect. The flow thermal parameters rapidly change when it International Journal of Gas Turbine, Propulsion and Power Systems April 2020, Volume 11, Number 2 Copyright © 2020 Gas Turbine Society of Japan Presented at International Gas Turbine Congress 2019 Tokyo, November 17-22, Tokyo, Japan Review Completed on February 25, 2020

The Real Gas Effect on the Stagnation Properties for Supercritical Carbon Dioxide Flows