Large-eddy Simulation of Realistic Gas Turbine Combustors

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y cold air influx through the dilution holes. This reduces the exit temperature considerably. The prediction of mass-splits through different components was shown to be within 5% of the experimental data for the cold and reacting flow simulations [1, 11] and are not repeated here. In addition, the average temperature in the measurement plane is within 2% of the experimental data. The comparison of the radial variation of the mean temperature is shown in Fig. (11) and was obtained by taking azimuthal average over the sector. This represents our first attempt to perform such large-scale simulations in realistic configurations and the results give considerable insight into the combustor spray-flame dynamics. This computation has been performed on 80 processors of ASC Frost (IBM SP3) and involved around 0.6M computational particles. It takes around 25-30 CPU-days on ASC Frost to obtain statistics over 40 time units (3-4 flow through times) starting from a statistically stationary solution. Significant advances in numerical algorithms resulting in efficient speedup of the solver are underway [26]. These new algorithms are expected to make possible such a multiphysics, multiphase computation of the full 18 injector combustor on 100M control volumes within 120- 150 CPU-hrs on the full ASC Frost machine (1024 processors). In addition, advanced models for prediction of pollutants and NOx are being developed and applied to compute their distributions within the combustion chamber. A variety of flow conditions including cruise, high power, takeoff etc. are also being simulated for multiple sectors of the combustor. 6 Summary & Future Work A non-dissipative, energy-conserving numerical solver for arbitrary-shaped unstructured grids is developed to simulate multiphase, multiscale turbulent reacting flows in realistic gas-turbine combustors. This numerical tool solves low-Mach number, variable density flow equations for the gas-phase. Advanced models to capture atomization & droplet breakup, droplet evaporation, droplet deformation & drag, and turbulent combustion have been developed to simulate complex multiphase reacting flows. In this paper, we emphasize the necessity of performing detailed validation and verification studies to assess the predictive capability of the numerical 22
solver as well as the models used. A series of validation cases in canonical configurations were selected to systematically evaluate each component of the numerical solver: particle-laden flows, evaporating droplets, gas-phase combustion, and droplet breakup. Results predicted show good agreement with the experimental data. Having verified the good predictive capability, a spray patternation study for PW injector and a multiphysics, multiscale simulation of reacting flow in one sector of the PW combustor were performed to give encouraging results and considerable insight into the unsteady flow development inside the combustor. Advanced numerical schemes handling primary atomization and liquid sheet breakup [29], finite-size effects of the droplets in the dense-spray regime [30], models for liquid-film formation [31], droplet dispersion [16], models based on concepts of micro-mixing for droplet flame interactions, advanced combustion models for premixed/partially premixed turbulent flames, soot and pollutant formation, and radiation are being developed. In addition, a highly accurate numerical scheme capturing acoustic waves without the stringent acoustic CFL-restriction in compressible flows has been developed to investigate combustion instabilities [32]. An extensive effort is ongoing to make this tool efficient (by using multigrid solvers, dynamic load-balancing techniques), modular, user-friendly and capable of solving relevant industrial problems with quick turn around time to suit the demands of combustor design cycle in aircraft industry. 7 Acknowledgement Support for this work was provided by the United States Department of Energy under the Accelerated Strategic Computing (ASC) program and NASA’s UEET program. The computations were performed on Blue Horizon at San Diego supercomputing center and ASC Frost at Lawrence Livermore National Laboratory. We are grateful to the Pratt & Whitney’s combustor group for providing important data for validation. The help provided by Prof. Krishnan Mahesh (University of Minnesota), Drs. Gianluca Iaccarino, Frank Ham, Prof. Heinz Pitsch (Stanford University), and Prof. George Constantinescu (University of Iowa) is highly appreciated. 23
Page 1 and 2: Large-eddy Simulation of Realistic
Page 3 and 4: flows. In LES, three-dimensional, u
Page 5 and 6: in the continuity, Ṡ m , mixture
Page 7 and 8: 2.4 Liquid-Phase Equations The drop
Page 9 and 10: more width than height with deforma
Page 11 and 12: mass, d p = (6m p /πρ p ) 1/3 . T
Page 13 and 14: 3 Numerical Method A co-located, fi
Page 15 and 16: with sudden expansion. The primary
Page 17 and 18: through times. A convective boundar
Page 19 and 20: correctly represent the injector fl
Page 21: 5 Validation of Multi-physics React
Page 25 and 26: [9] Apte, S. V., Mahesh, K., Moin,
Page 27 and 28: [30] Apte, S.V., Mahesh, K., and Lu
Page 29 and 30: 0.001 0.003 0.006 0.008 0.011 0.013
Page 31 and 32: 0.5 t=0.18 ms y, cm 0 -0.5 0 0.5 1
Page 33 and 34: y 6 4 2 0 (a) inlet wall outer swir
Page 35 and 36: Normalized Axial Mass Flowrate 8 6

Large-eddy Simulation of Realistic Gas Turbine Combustors

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