Performance analysis of radial-inflow turbine of ORC: New combined approach of preliminary design and 3D CFD study

Abstract

A new methodology for the aerothermodynamic design of radial-inflow turbines used in organic Rankine cycles is presented. Initially, a fully detailed one-dimensional analysis was performed, where the real gas properties of R123 are calculated using the REFPROP© software. The developed model was validated against the most recent studies. Next, a 3D CFD analysis of the nozzle and the rotor was carried out using ANSYS-CFX® software. The 3D CFD method considered the influence of the rotor shroud curvature, which strongly influences the performance characteristics. The variations of this parameter allowed us to obtain uniform velocity contours, better blade loading and avoided the flow separation observed in the first attempt geometry. A comparison between the 1D mean-line and 3D CFD approach showed good agreement, validating the reliability of the two approaches. Also, an analysis of the 3D flowfield for different pressure ratios was performed to verify the quality of the method. The developed methodology has proven to be an appropriate tool for the radial-inflow ORC turbines design, which integrates uni- and three-dimensional models, for the prediction and improvement of the performance characteristics. The integration of these two approaches results in a novel procedure, since some phenomena associated with the three-dimensional characteristics of flow cannot be analyzed in detail in the one-dimensional analysis and are only possible to detect by a complete 3D CFD study.