Two codes have been developed for use in the preliminary aerodynamic design of radial inflow turbines. Both use a one-dimensional approximation for the flow through the machine along with empirical correlations for estimating the losses. This is known as meanline analysis. The first code, known as RITMLD (for Radial Inflow Turbine Meanline Design Operating Point), is used to obtain the main geometric parameters of the turbine based on the required performance at the design operating point. The

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... econd code, RITMLO (for Radial Inflow Turbine Meanline Off-Design Operating Point), is then used to predict the performance at off-design values of mass flow rate and rotational speed. The codes were intended for use in designing the turbines for closed-cycle gas turbine engines employing super-critical carbon dioxide (S-CO 2 ) as the working fluid. Since S-CO 2 behaves as a non-ideal gas, the codes use real gas properties throughout the analysis. The codes can be used for any other ideal or non-ideal gas by substituting calls to the appropriate fluid property subroutines from the National Institute for Standards and Technology (NIST). After a specific turbine was designed using RITMLD, the flow was analyzed in detail using ANSYS-CFX, a three-dimensional Computational Fluid Dynamics (CFD) code. The goal was to assess how accurately the performance is predicted by the simple meanline analysis. Furthermore, since it is novel to predict the full off-design characteristics using the meanline approach, CFX was also used to calculate the off-design performance. The comparison of results between meanline and CFD analyses show that the general trends of full turbine characteristics are similar for both prediction methods. ii