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Research Papers: Gas Turbines: Microturbines and Small Turbomachinery

# Computational Fluid Dynamics of a Radial Compressor Operating With Supercritical CO2

[+] Author and Article Information
Rene Pecnik

e-mail: r.pecnik@tudelft.nl

Piero Colonna

Process and Energy Department,
Delft University of Technology,
Leeghwaterstraat 44, 2628 CA Delft,
The Netherlands

1Corresponding author.

Contributed by International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 19, 2012; final manuscript received July 5, 2012; published online October 11, 2012. Editor: Dilip R. Ballal.

J. Eng. Gas Turbines Power 134(12), 122301 (Oct 11, 2012) (8 pages) doi:10.1115/1.4007196 History: Received June 19, 2012; Revised July 05, 2012

## Abstract

The merit of using supercritical $CO2(scCO2)$ as the working fluid of a closed Brayton cycle gas turbine is now widely recognized, and the development of this technology is now actively pursued. $scCO2$ gas turbine power plants are an attractive option for solar, geothermal, and nuclear energy conversion. Among the challenges that must be overcome in order to successfully bring the technology to the market is that the efficiency of the compressor and turbine operating with the supercritical fluid should be increased as much as possible. High efficiency can be reached by means of sophisticated aerodynamic design, which, compared to other overall efficiency improvements, like cycle maximum pressure and temperature increase, or increase of recuperator effectiveness, does not require an increase in equipment cost, but only an additional effort in research and development. This paper reports a three-dimensional computational fluid dynamics (CFD) study of a high-speed centrifugal compressor operating with CO2 in the thermodynamic region slightly above the vapor–liquid critical point. The investigated geometry is the compressor impeller tested in the Sandia $scCO2$ compression loop facility. The fluid dynamic simulations are performed with a fully implicit parallel Reynolds-averaged Navier–Stokes code based on a finite volume formulation on arbitrary polyhedral mesh elements. In order to account for the strongly nonlinear variation of the thermophysical properties of supercritical CO2, the CFD code is coupled with an extensive library for the computation of properties of fluids and mixtures. A specialized look-up table approach and a meshing technique suited for turbomachinery geometries are also among the novelties introduced in the developed methodology. A detailed evaluation of the CFD results highlights the challenges of numerical studies aimed at the simulation of technically relevant compressible flows occurring close to the liquid–vapor critical point. The data of the obtained flow field are used for a comparison with experiments performed at the Sandia $scCO2$ compression-loop facility.

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## Figures

Fig. 1

The tabulated region in the temperature-density plane and schematic of the interpolation; (a) the tabulated region in the temperature-density plane, with the two tables which are separated by the saturation lines; (b) schematic of the interpolation applied in the look-up table

Fig. 2

Look-up table convergence and interpolation error using the density ρ and the internal energy e. The number of intervals is the same for the two independent variables. Dashed line represents a bilinear interpolation scheme, while the solid line shows the convergence rate for the interpolation scheme using the gradients at each surrounding node.

Fig. 3

Centrifugal compressor geometry and computational mesh

Fig. 4

Simulation results for P2 = 90 bar and shaft speed = 50 krpm plotted in the T-s diagram. (a) Averaged states of the compression process. The starting and the end state (black squares) of the compression are obtained by averaging the inlet and the outlet plane of the computational domain. (b) The point could represents all control volumes in the computational domain plotted in the T-s plane.

Fig. 5

The red surfaces show the two phase regions at the blade tip and the blade trailing edges for P2 = 90 bar and shaft speed = 50 krpm

Fig. 6

Pressure contour plots in planes at different span locations for P2 = 90 bar and shaft speed = 50 krpm

Fig. 7

Impeller performance for 50 krpm shaft speed

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