Simulation of the turbulent dense gas flow through the nozzle of an organic rankine cycle turbine

This paper presents the numerical investigation of real-gas effects occurring in the nozzle of an existing axial organic Rankine cycle turbine. Two-dimensional Reynolds-Averaged Navier- Stokes simulations are carried out using a computational fluid dynamics code which employs accurate models for the computation of the thermodynamic and transport properties of the working fluid. Two cases have been analyzed: The expansions starting from the subcritical conditions corresponding to the nozzle design point, and an expansion starting from supercritical conditions. The computations have been performed with two different thermodynamic models, the simple polytropic ideal gas equation of state (EoS) and a state-of-the-art multiparameter Span-Wagner EoS. For the computation of transport properties, two models have been employed, namely, a simple power law in the temperature and the more accurate (and complex) Chung model. The influence of the different fluid models on the computed flow field are discussed.