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

Abstract

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 assess 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 and employ a number of turbulence models 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-ε, k-ε RNG, k-ω, k-ω SST and k-ω Generalized while the RSM models are BSL, LRR, w-RSM and k-ε 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-ε model gives the highest loss coefficients and the lowest isentropic efficiencies while most of the RSM models indicate higher efficiencies and lower loss coefficients. At off-design conditions a sensitivity study revealed that the k-ε RNG model records the sharpest drop in the isentropic efficiency of 8.24% at low mass flowrate reaching 30% off-design. The efficiency sensitivity is found to be less for the other tested models getting 3.1% drop in efficiency for the LRR RSM model.

Design of a 130 MW Axial Turbine Operating with a Supercritical Carbon Dioxide Mixture for the SCARABEUS Project

“…A 3D steady-state multi-stage CFD model is set up for a single flow passage, as shown in Figure 3. The turbulence model is k-ω SST, which is widely considered for turbomachinery simulations [31]. Near the walls, a scalable wall function model is used, which employs equilibrium wall functions for high Reynold's number flow.…”

Efficient aerodynamic optimization of turbine blade profiles: an integrated approach with novel HDSPSO algorithm

“…The study employs the Euranus solver within the software for CFD simulations, using the finite volume method to solve the steady compressible RANS equation. The Shear-Stress Transport (SST) turbulence model accurately predicts flow separation, making it suitable for high-speed compressible turbomachinery problems (AbdElDayem et al ., 2021). The second-order accurate central-difference format is used for spatial discretization and the fourth-order Runge-Kutta method for temporal discretization.…”

Integrated Aerodynamic and Structural Blade Shape Optimization of Axial Turbines Operating With Supercritical Carbon Dioxide Blended With Dopants

“…The model definition of the proposed blends is presented in GTP-22-1269 Abdeldayem 7 List of tables Table 1. The model uses shear stress transport (k-ω SST) turbulence model as it has been found that this is the most suitable model for turbomachinery applications [30]. The interface between the stator and rotor domains is treated as a mixing plane which has proven to give high quality results with the least numerical instabilities compared to the frozen rotor approach [31].…”

“…Some deviations between the MLD and CFD model results are expected due to the inherent simplicity of the mean-line approach, and the limitations of the mean-line model in evaluating aerodynamic losses by using loss correlations developed for traditional working fluids. However, these have been investigated and quantified by the authors [30]. Absolute efficiency increase of 2.54 pp, 2.06 pp, and 1.76 pp is achieved for the sCO2-SO2, sCO2-C6F6, and sCO2-TiCl4 designs, respectively.…”