Research Papers

Design of an Annular-Radial Diffuser for Operation With a Supercritical CO2 Radial Inflow Turbine

[+] Author and Article Information
Joshua A. Keep

School of Mechanical and Mining Engineering,
The University of Queensland,
Brisbane, Queensland 4072, Australia
e-mail: j.keep@uq.edu.au

Ingo H. J. Jahn

School of Mechanical and Mining Engineering,
The University of Queensland,
Brisbane, Queensland 4072, Australia
e-mail: i.jahn@uq.edu.au

Manuscript received November 19, 2018; final manuscript received April 4, 2019; published online May 2, 2019. Assoc. Editor: David Sánchez.

J. Eng. Gas Turbines Power 141(8), 081020 (May 02, 2019) (12 pages) Paper No: GTP-18-1701; doi: 10.1115/1.4043431 History: Received November 19, 2018; Revised April 04, 2019

Radial inflow turbines are a relevant architecture for energy extraction from supercritical CO2 power cycles for scales less than 10 MW. To ensure stage and overall cycle efficiency, it is desirable to recover exhaust energy from the turbine stage through the inclusion of a suitable diffuser in the turbine exhaust stream. In supercritical CO2 Brayton cycles, the high turbine inlet pressure can lead to sealing challenges at small scale if the rotor is supported from the rotor rear side in the conventional manner. An alternative is a layout where the rotor exit faces the bearing system. While such a layout is attractive for the sealing system, it limits the axial space claim of the diffuser. Designs of a combined annular-radial diffuser are considered as a means to meet the aforementioned packaging challenges of this rotor layout. Diffuser performance is assessed numerically with the use of Reynolds-averaged Navier--Stokes (RANS) and unsteady Reynolds-averaged Navier--Stokes (URANS) calculations. To appropriately account for cross coupling with the stage, a single blade passage of the entire stage is modeled. Assessment of diffuser inlet conditions, and off-design performance analysis, reveals that the investigated diffuser designs are performance robust to high swirl, high inlet blockage, and highly nonuniform mass flux distribution. Diffuser component performance is dominated by the annular-radial bend. The incorporation of a constant sectional area bend is the key geometric feature in rendering the highly nonuniform turbine exit flow (dominated by tip clearance flows at the shroud) more uniform.

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Angelino, G. , 1967, “ Perspectives for the Liquid Phase Compression Gas Turbine,” ASME J. Eng. Power, 89(2), pp. 229–236. [CrossRef]
Feher, E. G. , 1968, “ The Supercritical Thermodynamic Power Cycle,” Energy Convers., 8(2), pp. 85–90. [CrossRef]
Dostal, V. , 2004, “ A Supercritical Carbon Dioxide Cycle for Next Generation Nuclear Reactors,” Ph.D. thesis, Massachusetts Institute of Technology, Cambridge, MA.
Moore, J. , Brun, K. , Evans, N. , and Kalra, C. , 2015, “ Development of 1 MWe Supercritical CO2 Test Loop,” ASME Paper No. GT2015-43771.
Wilkes, J. , Allison, T. , amd Schmidt, J. , Bennett, J. , Wyagant, K. , Pelton, R. , and Bosen, W. , 2016, “ Application of an Integrally Geared Compander to an sCO2 Recompression Brayton Cycle,” Fifth International Supercritical CO2 Power Cycles Symposium, San Antonio, TX, Mar. 28–31, Paper No. 055.
ASTRI, 2017, “ ASTRI Milestone 12 Report—For Public Dissemination,” Australian Solar Thermal Research Initiative (ASTRI), Newcastle, Australia, Report No. 1-SRI002.
Friedman, P. , and Dennis, R. , eds., 2017, Fundamentals and Applications of Supercritical Carbon Dioxide (sCO2) Based Power Cycles, 1st ed., Woodhead Publishing, Cambridge, UK.
Japikse, D. , and Baines, N. C. , 1998, Turbomachinery Diffuser Design Technology, Concepts Eti, Norwich, VT.
Wright, S. A. , Radel, R. F. , Vernon, M. E. , Rochau, G. E. , and Pickard, P. S. , 2010, “ Operation and Analysis of a Supercritical CO2 Brayton Cycle,” Sandia National Laboratories, Albuquerque, NM, Report No. SAND2010-0171.
Moustapha, H. , Zelesky, M. F. , Baines, N. C. , and Japikse, D. , 2003, Axial and Radial Turbines, Vol. 2, Concepts NREC, White River Junction, VT.
Sovran, G. , and Klomp, E. , 1965, “ Experimentally Determined Optimum Geometries for Rectilinear Diffusers With Rectangular, Conical or Annular Cross-Section,” Fluid Mechanics of Internal Flow—Proceedings of the Symposium of the Fluid Mechanics of Internal Flow, Elsevier, Hoboken, NJ.
Moller, P. S. , 1966, “ A Radial Diffuser Using Incompressible Flow Between Narrowly Spaced Disks,” ASME J. Basic Eng., 88(1), pp. 155–162. [CrossRef]
Keep, J. A. , Head, A. J. , and Jahn, I. H. , 2017, “ Design of an Efficient Space Constrained Diffuser for Supercritical CO2 Turbines,” J. Phys.: Conf. Ser., 821(1), p. 012026. [CrossRef]
Japikse, D. , and Pampreen, R. , 1979, “ Annular Diffuser Performance for an Automotive Gas Turbine,” ASME J. Eng. Gas Turbines Power, 101(3), pp. 358–372. [CrossRef]
Sovran, G. , and Klomp, E. , 1967, “ Experimentally Determined Optimum Geometries for Rectilinear Diffusers With Rectangular, Conical or Annular Cross Section,” Fluid Mechanics of Internal Flow, G. Sovran , ed., Elsevier, Amsterdam, The Netherlands.
Zhu, Y. , and Sjolander, S. A. , 1987, “ Effect of Geometry on the Performance of Radial Vaneless Diffusers,” ASME J. Turbomach., 109(4), pp. 550–556. [CrossRef]
Kluß, D. , Stoff, H. , and Wiedermann, A. , 2009, “ Effect of Wakes and Secondary Flow on Re-Attachment of Turbine Exit Annular Diffuser Flow,” ASME J. Turbomach., 131(4), p. 041012. [CrossRef]
Kuschel, M. , and Seume, J. , 2011, “ Influence of Unsteady Turbine Flow on the Performance of an Exhaust Diffuser,” ASME Paper No. GT2011-45673.
Hirschmann, A. , Volkmer, S. , Schatz, M. , Finzel, C. , Casey, M. , and Montgomery, M. , 2011, “ The Influence of the Total Pressure Profile on the Performance of Axial Gas Turbine Diffusers,” ASME J. Turbomach., 134(2), p. 021017. [CrossRef]
Volkmer, S. , Schatz, M. , Casey, M. , and Montgomery, M. , 2013, “ Prediction of Flow in an Exhaust Gas Turbine Diffuser With a Scale-Adaptive Simulation Model,” ASME Paper No. GT2013-94954.
Drechsel, B. , Mller, C. , Herbst, F. , and Seume, J. , 2015, “ Influence of Turbulent Flow Characteristics and Coherent Vortices on the Pressure Recovery of Annular Diffusers—Part B: Scale-Resolving Simulations,” ASME Paper No. GT2015-42477.
Keep, J. , and Jahn, I. , 2018, “ Numerical Loss Breakdown Study for a Small Scale, Low Specific Speed Supercritical CO2 Radial Inflow Turbine,” GPPS Montreal 18, Montreal, QC, Canada, May 7–9, Paper No. GPPS-NA-2018-0071.
Rohlik, H. E. , 1968, “ Analytical Determination of Radial Inflow Turbine Design Geometry for Maximum Efficiency,” National Aeronautics and Space Administration, Washington, DC, Report No. TN D-4384.
Qi, J. , Reddell, T. , Qin, K. , Hooman, K. , and Jahn, I. , 2017, “ Supercritical CO2 Radial Turbine Design Performance as a Function of Turbine Size Parameters,” ASME J. Turbomach., 139(8), p. 081008. [CrossRef]
Moor, J. , Brun, K. , Evans, N. , Bueno, P. , and Kalra, C. , 2014, “ Development of a 1 Mwe Supercritical CO2 Brayton Cycle Test Loop,” Fourth International Symposium—Supercritical CO2 Power Cycles, Pittsburg, PA, Sept. 9–10, Paper No. 047.
ANSYS, 2018, “CFX Solver Theory Guide 18.1,” Canonsburg, PA.
Menter, F. R. , 1994, “ Two-Equation Eddy-Viscosity Turbulence Models for Engineering Applications,” AIAA J., 32(8), pp. 1598–1605. [CrossRef]
Menter, F. , Kuntz, M. , and Bender, R. , 2003, “ A Scale-Adaptive Simulation Model for Turbulent Flow Predictions,” AIAA Paper No. 2003-0767.
Menter, F. , and Egorov, Y. , 2005, “ A Scale Adaptive Simulation Model Using Two-Equation Models,” AIAA Paper No. 2005-1095.
Simpson, A. , Spence, S. , and Watterson, J. , 2013, “ Numerical and Experimental Study of the Performance Effects of Varying Vaneless Space and Vane Solidity in Radial Turbine Stators,” ASME J. Turbomach., 135(3), p. 031001. [CrossRef]
White, M. , and Sayma, A. I. , 2015, “ The Application of Similitude Theory for the Performance Prediction of Radial Turbines Within Small-Scale Low-Temperature Organic Rankine Cycles,” ASME J. Eng. Gas Turbines Power, 137(12), p. 122605. [CrossRef]
Bell, I. H. , Wronski, J. , Quoilin, S. , and Lemort, V. , 2014, “ Pure and Pseudo-Pure Fluid Thermophysical Property Evaluation and the Open-Source Thermophysical Property Library Coolprop,” Ind. Eng. Chem. Res., 53(6), pp. 2498–2508. [CrossRef] [PubMed]
Jahn, I. , and Keep, J. , 2017, “ On the Off-Design Performance of Supercritical Carbon Dioxide Power Cycles,” Shanghai 2017 GPPF, Shanghai, China, Oct. 11–Nov. 1, Paper No. GPPS-2017-0049.


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Fig. 1

Cantilevered rotor layouts: (a) conventional arrangement and (b) the proposed arrangement

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Fig. 2

A diffuser with arbitrary annular geometry

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Fig. 3

Sectional view of proposed geometry for analysis

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Fig. 4

Section view of diffuser geometries

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Fig. 5

Section view of a typical diffuser mesh

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Fig. 6

Mass flow averaged diffuser inlet pressure versus number of blade passes for different time-step values

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Fig. 7

Average diffuser inlet pressure versus number of blade passes for the selected time-step value

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Fig. 8

Diffuser inlet streamwise velocity for selected geometries

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Fig. 9

Diffuser on-design performance as a function of geometry: (a) Cp versus a and (b) K versus a

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Fig. 10

Diffuser pressure rise coefficient (Cp) along diffuser passage for selected geometries: (a) a = 0.075, (b) a = 0.1, (c) a = 0.15, and (d) a = 0.175

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Fig. 11

Diffuser total pressure loss coefficient (K) along diffuser passage for selected geometries: (a) a = 0.075, (b) a = 0.1, (c) a = 0.15, and (d) a = 0.175

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Fig. 12

Diffuser streamwise velocity (hub to shroud) at inlet (A), start of radial section (B), and end (C) for selected geometries. Stations shown in Fig. 3: (a) a = 0.075, (b) a = 0.1, (c) a = 0.15, and (d) a = 0.175.

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Fig. 13

Diffuser off-design performance for geometry a =0.15. See Table 4 for conditions: (a) Cp and (b) K.

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Fig. 14

Turbine stage efficiency at nominal flow conditions as a function of geometry, measured at locations shown in Fig. 3

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Fig. 15

Diffuser performance comparison for geometry a =0.15 by simulation type. Performance calculated at inlet (A), start of radial section (B), and end (C): (a) diffuser streamwise velocity and (b) diffuser pressure rise coefficient (Cp).



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