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Numerical Modeling of Compressor and Combustor Flows

Numerical Modeling of Compressor and Combustor Flows. Suresh Menon, Lakshmi N. Sankar Won Wook Kim S. Pannala, S. Niazi, C. Rivera, A. Stein School of Aerospace Engineering Georgia Tech, Atlanta, GA 30332-0150.

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Numerical Modeling of Compressor and Combustor Flows

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  1. Numerical Modeling of Compressor and Combustor Flows Suresh Menon, Lakshmi N. Sankar Won Wook Kim S. Pannala, S. Niazi, C. Rivera, A. Stein School of Aerospace EngineeringGeorgia Tech, Atlanta, GA 30332-0150

  2. Develop first-principles based tools for modeling flow through axial and centrifugalcompressors. Develop first-principles based tools formodeling two-phase reacting flowwithin combustors. Use these tools to explore control strategiesfor stable operation of compressors and combustors. RESEARCH OBJECTIVES

  3. A two-dimensional rotor-stator Navier-Stokes code has been developed, and used to model rotating stall. A reduced order model based on 2-D simulations has been developed, and validated. 3-D Navier-Stokes simulations have beencompleted for a NASA centrifugal compressor configuration. Stable operation of the 3-D configuration has beenachieved at low mass flow rates using passive control devices. Compressor Modeling: Progress To Date

  4. Solves compressible Navier-Stokes equations for Rotor-Stator Configurations. Can model oscillating blades, inflowand downstream disturbances. Has been extensively validated. (Rivera, Ph. D. Dissertation, May 1998.) Some validation studies were presented last year. Forms the basis for the new Reduced Order Model. Two-Dimensional Flow Solver

  5. 7 4 8 1 5 2 9 6 3 REDUCED ORDER MODEL Flow Field is divided into Macro-zones. In each zone, there are 4 states - r, u, v and T

  6. Neighbor Zone Current Zone Neighbor Zone Neighbor Zone Neighbor Zone Reduced Order Model II In each zone, the governing equations are applied: A coupled system of ODEs result.

  7. Reduced Order Model III • This system of simultaneous nonlinear ordinary differential equations couples states from all the zones • Steady state solution yields performance map. • The unsteady solution may be used to analyze the nonlinear dynamics of the system.

  8. Compressor Performance Map

  9. 7 4 8 1 5 2 9 6 3 REDUCED ORDER MODEL Throttle effects may be inexpensively modeled, and system transients studied. Incoming Disturbances may be inexpensively modeled.

  10. NASA Low Speed Centrifugal Compressor SIMULATION SETUP • 20 Full Blades with 55° Backsweep • Inlet Diameter 0.87 m • Exit Diameter 1.52 m • Design Conditions: • Mass Flow Rate 30 kg/sec • 1862 RPM • Total Pressure Ratio 1.14

  11. Single Passage Grid Modeling 3-D SIMULATION SETUP Grid Size: 129x61x41 = 322,629 points

  12. 3-D SIMULATION SETUP Boundary Conditions Inlet: p0,T0,v,w specified; Characteristic equation solved to model acoustic waves leaving the domain. Diffuser Exit: pback specified; entropy and vorticity are extrapolated from Interior. Periodic Boundaries: Flow properties are periodic from blade to blade. Blade Surface: no-slip velocity conditions.

  13. Surface Pressure Distribution Computations Vs. Measurements

  14. Surface Pressure Distribution Computations Vs. Measurements

  15. CFD without bleeding Compressor Performance Characteristics

  16. Grid Sensitivity Impeller Performance Map for LSCC

  17. Velocity Field (Colored by Pressure) RESULTS (Design Conditions) Diffuser Region is Well BehavedNo Separation

  18. RESULTS (Off-Design Conditions) Velocity Field (Colored by Pressure) Diffuser Region Shows Small SeparationOnset of Instabilities

  19. Effects of Bleeding on Diffuser Performance With bleed Without bleed

  20. Compressor Simulations: Conclusions • A new CFD based reduced order model has been developed and validated. • A 3-D unsteady compressible flow solver for modeling centrifugal compressors has been developed and validated. • Good agreement with experiments have been obtained for a Low Speed Centrifugal Compressor (LSCC) tested at NASA Lewis Research Center. • For the LSCC, flow instabilities were found to originate in the diffuser region. • Stall control by the use of bleed valves on the diffuser walls has been computationally demonstrated.

  21. A stand-alone methodology for droplet convection,vaporization, turbulent mixing and chemical reaction has been developed, and was reported last year. During the current period, this methodology wassuccessfully coupled to gas-phase unsteady flow solvers. Incompressible and compressible versions of thetwo phase flow solvers have been developed. Ability of the methodology to track particles injected into a vortex has been verified. Validation against Ga Tech experiments are in progress. Combustor Modeling- Progress To Date

  22. Droplets below a cut-offradius are modeled in thesubgrid till vaporizationis complete. Energy, Mass Transferred to subgrid. Momentum transferredto the supergrid. Droplets see local flow properties(Temperature and Velocity). Droplet Trajectory

  23. Present subgrid approach is more efficient than other LES schemes where a very fine multi-dimensional subgrid is needed to model the droplets. In conventional Lagrangian schemes, all the coupling between the droplet and the gas phase is via the supergrid. In the present approach, only the momentum of gas and liquid phase is coupled via the supergrid. Conventional Lagrangian schemes assume droplets vaporize instantaneously, below a cut-off radius.This can give erroneous results. Features of the Present Approach

  24. Seed Particles Mixing Layer Simulations with Droplets 3-D Shear layer, on which diturbances corresponding to first unstable mode are imposed.

  25. Present Model Correctly ModelsLarge and Small Particles St=Stokes No.

  26. Simulation of a Mixing Layer, where the upper stream is laden with medium size particles (Stokes No. = 1). Experiment by Lazaros and Lasheras (1992)

  27. Conventional LES Scheme Vs. Present5 Micron Cut-Off Product mass Fraction

  28. Conventional LES Scheme Vs. Present5 Micron Cut-Off Temperature

  29. Conventional LES Results are sensitive to Droplet Cut-Off Size 4 to 5 times expensive than present approach

  30. Present Approach is less sensitive toDroplet Cut-Off Size

  31. Honeycomb Optical Access Measurement Planes Optical Access TurbulenceGenerator Experimental Set Up for LES/LEM Validation main Air Fuel Coflow Air Main Air

  32. Comparisons with GA Tech Experiments Measured inflow velocities, droplet distribution and turbulence levels are input into the code

  33. Comparisons with Ga Tech Experiments

  34. Incompressible and Compressible Two-Phase Reacting Flow Solvers have been developed. Droplet convection, evaporation, turbulent mixing and reaction are all modeled from first principles. Present approach is less expensive than conventional LES, but more accurate. Flow solver has been validated with experiments. Combustor Modeling- Conclusions

  35. Extend the new CFD based reduced order model to 3-D centrifugal configurations. Validate. Study stall and surge control of the Ga Tech centrifugal compressor configuration using CFD, and using the 3-D reduced order model. Perform further validations of the LES/LEM two-phase flow method with Georgia Tech data. Perform two-phase reacting flow simulations for a dump combustor configuration. Research Plans for Next Year

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