THE INFLUENCE OF REAL GAS EFFECTS ON ICE-ORC TURBINE FLOW FIELDS

This paper presents a quantitative comparison of the flow fields of a radial turbine between real gas and perfect gas models for the internal combustion engine (ICE) organic Rankine Cycle (ORC) application. Three-dimensional turbulent Navier-Stokes simulations are carried out using CFD code NUMECA FINE (TM)/TURBO, which is linked to an accurate thermodynamic model for organic working fluid R123 in the form of thermodynamic tables. Four turbine operating conditions including the design point and three part-load points, the inlet compressibility factors of which are 0.82-0.89, are analyzed to discuss the differences of flow fields. Obvious derivations of thermodynamic parameters are investigated in the turbine flow fields. The derivations of speed of sound and density at the nozzle inlet are about 15-20%. There exist about 10m/s value differences in the nozzle outlet velocity evaluation, and furthermore a difference of 10 degrees in the rotor inlet incidence angle comparison. The derivations of relative Mach number are about 20-35% in the rotor outlet near the shroud surface. More than 30% differences are shown in the comparison of turbine total temperature drops. Other thermodynamic parameters show much smaller derivations. The differences of thermodynamic parameters lead to a 1-3% larger in mas flow rate, 1-2% larger in isentropic efficiency and 6-8% smaller in specific power comparison. However, there do not exist obvious differences on thermodynamic parameters distributions in the flow fields. The similar flow fields provide a suggestion that perfect gas model may be an acceptable model for turbine preliminary design and one-dimensional analysis in this gas thermodynamic region, and also the real gas flow fields simulated can be used as a start point to refine the turbine design.