A detailed loss assessment of an axial turbine stage operating with a supercritical carbon dioxide (sCO2) based mixture, namely titanium tetrachloride (CO2-TiCl4 85-15%), is presented. To quantify aerodynamic losses, computational fluid dynamics (CFD) simulations are conducted using a geometry generated using mean-line design equations which is part of the work delivered to the SCARABEUS project [1]. The CFD simulations are 3D steady state using a number of turbulence models used to investigate various aerodynamic loss mechanisms. Two categories of turbulence models are used: Eddy Viscosity and Reynold’s Stress models (RSM). The Eddy Viscosity models are the k-e, k-e RNG, k-w, k-w SST and k- w Generalized while the RSM models are BSL, LRR, w-RSM and k-e EARSM. The comparison between different turbulence models showed minor deviations in mass-flow rate, power output and blade loading while significant deviations appear in the loss coefficients and the degree of reaction. It is noted that the k-e model gives the highest loss coefficients and the lowest isentropic efficiencies while most of the RSM models indicate higher efficiencies and low loss coefficients. At off-design conditions a sensitivity study showed a sharp drop in the isentropic efficiency using all turbulence models at very low mass-flow rates.

Comparison of Cfd Predictions of Supercritical Carbon Dioxide Axial Flow Turbines Using a Number of Turbulence Models

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2021/volume/84898

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