Accurate CFD Analysis of a Radial Compressor Operating with Supercritical CO2

by Rene Pecnik & Piero Colonna
Delft University of Technology

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High effciency of the compressor and the expander is the key to reach high overall conversion effciency in gas turbine power plants. While there has been enormous progress in the design of turbomachinery operated on steam and air, fluids behaving like ideal gases, there have been only a few studies covering the unconventional flow behavior of fluids whose thermodynamic properties are in the range of the vapor-liquid critical point [1, 2]. Often, the design of the turbomachinery components operating with supercritical fluids is based on one-dimensional models taking into account real gas effects by means of surrogate fluid models [3]. Fluid properties close to the critical point strongly deviate from the ideal gas law and, even more importantly, exhibit strong variations. Flows whose thermodynamic properties encompass the critical region are therefore highly unconventional and the gas dynamics of dense and supercritical fluids remain largely unexplored. The aerodynamic design of turbomachinery operating in the close-to-critical region can greatly benefit from high-fidelity flow simulations.

In this paper we present a three-dimensional CFD study of a centrifugal compressor operating with CO2 in the thermodynamic region slightly above the vapor-liquid critical point. The geometry investigated is based on the experimental compressor operating in the loop test facility running at Sandia National Laboratories, Albuquerque, New Mexico [3]. The CFD simulations are performed with a fully implicit parallel Reynolds-averaged Navier-Stokes code based on a finite volume formu-lation on arbitrary polyhedral mesh elements. The CFD code has been validated with test cases that are relevant for this study in [4]. In order to account for the real gas behavior of supercritical CO2 the CFD code is coupled with the FluidProp thermodynamic library [5], using an accurate equation of state model for CO2 [6, 7].

The CFD results will be evaluated with respect to the predicted compressor effciency compared to measurements performed at Sandia National Laboratories and to the results obtained with current state of the art 1-dimenional design tools reported in [3].

References

  1. Colonna, P., Harinck, J., Rebay, S. & Guardone, A. 2008 Real-gas effects in organic Rankine cycle turbine nozzles. J. Propul. Power, Vol. 24, pp. 282-294
  2. Takagi, K., Muto, Y., Isahizuka, T., Kikura, H. and Aritomi, M. 2010 Research on Flow Characteristics of Supercritical CO2 Axial Compressor Blades by CFD Analysis. J. Power and Energy Systems, Vol. 4(1)
  3. Wright, S.A., Radel, R.F., Vernon, M.E., Rochau, G.E. & Pickard, P.S. 2010 Operation and Analysis of a Supercritical CO2 Brayton Cycle. Sandia Report 2010-0171
  4. Pecnik, R., Witteveen, J., Iaccarino, G. 2011 Uncertainty Quantification for Laminar-Turbulent Transition Prediction in RANS Turbomachinery Applications AIAA-2011-660
  5. Colonna, P. and Van der Stelt, T. 2005 Fluidprop: A program for the estimation of thermophysical properties of fluids. Energy Technology section, Delft University of Technology, The Netherlands (www.fluidprop.com).
  6. Span, R. and Wagner, W. 2003 Equations of State for Technical Applications. I. Simultaneously Optimized Functional Forms for Nonpolar and Polar Fluids. Int. J. Thermophys. 24(1), pp. 1–39
  7. Span, R. and Wagner, W. 2003 Equations of State for Technical Applications. II. Results for Nonpolar Fluids. Int. J. Thermophys. 24(1), pp. 41–109