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Operation and Modeling of Turbogenerators - Hsing-pang Liu - June 2010

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  • 1. 2010 ESRDC Team Meeting
    Operation and Modeling of Turbogenerators
    Hsing-Pang Liu
    Center for Electromechanics, University of Texas at Austin
    Ruixian Fang
    Department of Mechanical Engineering, University of South Carolina
    June 3, 2010
  • 2. Operation Basis and Modeling Goal
    Gas turbines are primarily used for jet aircraft propulsion and power generation.
    Operation of gas turbines is based on thermodynamics principles and constitutive relations of heat transfer and fluid mechanics.
    The goal of ESRDC gas turbine modeling effort is to perform transient dynamic modeling and simulation of generic gas turbines.
  • 3. Initial Effort
    Contact various UT ESRDC team personnel to find out what has been done on the gas turbine modeling in the past
    Obtain technical information on gas turbine design, modeling, simulation, and testing through literature search
    Search existing gas turbine modeling/simulation software for potential use in electric ship power generation application
    Download several identified gas turbine modeling software for free trial and evaluation
  • 4. Commercial Gas Turbine Software Identified
    • Gas Turbine Simulation Program “GSP”
    • 5. Developed by Netherlands National Aerospace Laboratory NLR
    • 6. Any gas turbine configuration
    • 7. Steady-state and transient off-design simulations
    • 8. GSP LE (Light Edition) downloaded for evaluation
    • 9. “GasTurb 11”
    • 10. Developed by Dr. Joachim Kurzke (retired from Germany’s aircraft engine manufacturer MTU Aero Engines)
    • 11. Simulates most common types of gas turbines for propulsion and for power generation
    • 12. Simulates transient operation of gas turbines
    • 13. Component maps offered in GasTurb are all taken from open literature
    • 14. Supports modeling of engines based on a limited amount of information
    • 15. Entry -level version downloaded for evaluation
    • 16. Numerical Propulsion System Simulation “NPSS”
    • 17. Originally developed by NASA Glenn Research Center and its industrial/government partners for military jet engine applications and space transportation
    • 18. A consortium was later created to ensure continued development and enhancement
    • 19. Latest version of NPSS 2.2.1 has been released for commercial distribution
    • 20. Steady-state and transient off-design performance prediction
    • 21. NIST (National Institute of Standards and Technology) compliant thermodynamic gas-properties package
    • 22. Evaluation edition with basic functionality downloaded for evaluation
  • Commercial Gas Turbine Software Identified(Continued)
    • “VisSim Gas Turbine Simulator”
    • 23. Developed by Visual Solutions Inc.
    • 24. Steady-state and transient behavior
    • 25. Downloaded for evaluation
    • 26. “GT PRO”
    • 27. Developed by THERMOFLOW
    • 28. Gas turbine combined cycle design program (mainly for gas turbine power plants)
    • 29. “GPAL Gas Turbine Simulators”
    • 30. Developed by Gas Path Analysis Limited
    • 31. Single-shaft gas turbine (used in power generator)
    • 32. Two-shaft gas turbine operating with a free power turbine (used in mechanical drive applications)
    • 33. “Flowmaster V7.7 Gas Turbine”
    • 34. Developed by Flowmaster
    • 35. Design and simulation of gas turbine thermo-fluid systems
  • Gas Turbine Simulation Program “GSP”
    History
    • Initiated at Aerospace Department of Delft Technical University (in 1986) where NASA's DYNGEN program was used for jet and turbofan engine simulations
    • 36. First version of GSP developed by inheriting features from DYNGEN, combined with improved stability and speed of numerical iteration processes
    • 37. Implemented in object-oriented Borland Delphi environment in 1996
    • 38. Now has an user-friendly drag&drop interface on Windows
    Modeling Approach
    • Zero-dimensional modeling of processes in different gas turbine components with aero-thermodynamic relations and steady state characteristics (component maps)
    • 39. Air and gas properties thermodynamically averaged over the flow cross-sectional areas at inlet and exit of each component module
    • 40. A pre-defined design point is calculated first from a set of design point data
    • 41. For “off-design” modeling, deviation from the design point is calculated by solving a set of non-linear differential equations, which include conservation of mass, momentum, and energy for all components
    • 42. For a transient simulation, the differential equations include time-derivatives; in each time step, dynamic effects are calculated and the solution represents a quasi-steady state operating point
  • Gas Turbine Engine Simulations Using “GSP”
    To date, GSP has been used for simulation of a large number of gas turbine engines including
    GE J85-GE-15 (afterburning turbojet)
    PW JT15D (turbofan)
    F100-PW-200 (afterburning turbofan)
    F100-PW-220 (afterburning turbofan)
    F100-PW-229 (afterburning turbofan)
    RR Avon (turbojet)
    RR TAY 620 (turbofan)
    Allison 250-C20B (turboshaft)
    JSF PW119 (afterburning turbofan with lift fan and clutch)
    JT15D4 (turbofan)
    T55 (turboshaft)
    T800 (turboshaft)
    CFM-56 (turbofan)
    CF6-50 (turbofan)
    CF6-80 (turbofan)
    GT10 (industrial turboshaft)
    LM2500 (industrial turboshaft)
    MTT Mk4 (micro turbine)
    PW4056 (turbofan)
    PW100 family (turboprop)
    RTM322 (turboshaft)
    Rover (turboshaft)
    Typhoon (turboshaft)
    RR Gem 40/42 (turboshaft)
    Turblow (air compressor / gas turbine)
    OPRA (recuperated turboshaft)
    AE3007 (turbofan)
    Siemens V64.3 (heavy duty)
    MS9001FA (heavy duty 'frame 9')
    Bio-mass gasifiers integrated with industrial gas turbine.
    These models have been developed at National Aerospace Laboratory NLR and some of them include proprietary data
  • 43. Another Thermodynamic Simulation Code (Cycle-Tempo)
    A thermodynamic simulation code developed by Delft University of Technology (Netherlands)
    A program for thermodynamic modeling and optimization of systems for production of electricity, heat, and refrigeration
    Capable of modeling steady-state behavior of generic gas turbine engines (NOT transient dynamic gas turbine simulation)
    Well-documented and relatively simple
    Used to build a gas turbine engine model to predict the steady-state performance at the engine’s design point
    Compare the steady-state results, at engine’s design point, predicted by “Cycle-Tempo” with those predicted by other commercial software
  • 44. Gas Turbine Engine Baseline Model (Used for Software Evaluation)
    Gas turbine engine chosen for evaluation
    • Rolls-Royce MT30 (MT stands for Marine Trent) gas turbine engine
    • 45. Selected by US Navy to power IPS EDM, DDG 1000, and Littoral Combat Ship (LCS)
    • 46. Selected by UK MOD to power Royal Navy’s future all-electric aircraft carrier
    • 47. A multi-spool engine and is composed of intermediate-pressure and high-pressure compressors (IPC and HPC) and high-pressure, intermediate-pressure, and free-power turbines (HPT, IPT, FPT)
    • 48. General engine description and engine performance characteristics, available in Rolls-Royce “Fact Sheet” and open literature, obtained from Holsonback’s thesis (UT-Austin, 2007) provided by Dr. Tom Kiehne
    Modeling and simulation
    • Predict steady-state performance at engine’s design point
    • 49. Compare results predicted by “Cycle-Tempo“ and “GSP”
    • 50. Once the steady-state results at the design point match well, transient dynamic off-design simulations will then be attempted by using “GSP”
    Difficulties encountered
    • Many required component input data (i.e., compression pressure ratios of IPC and HPC, expansion pressure ratios of HPT, IPT, and FPT, and isentropic efficiencies of IPC, HPC, HPT, IPT, and FPT) are not available from Rolls-Royce
    • 51. Educated guesses and multiple iterations required
  • Rolls-Royce MT30 Gas Turbine Engine
  • 52. MT30 Steady-State Performance at Design Point(Predicted by Cycle-Tempo)
  • 53. MT30 Steady-State Performance at Design Point(Predicted by GSP)
  • 54. Comparison of Predicted Component Parameters
    Intermediate-pressure compressor
    • Outlet air temperature = 231.05oC (Cycle-Tempo), 231.51oC (GSP)
    • 55. Outlet air pressure = 5.79 bar (Cycle-Tempo), 5.79 bar (GSP)
    • 56. Power input = 24448 kW (Cycle-Tempo), 24365 kW (GSP)
    High-pressure compressor
    • Outlet air temperature = 509.25oC (Cycle-Tempo), 510.46oC (GSP)
    • 57. Outlet air pressure = 24.32 bar (Cycle-Tempo), 24.32 bar (GSP)
    • 58. Power input = 32944 kW (Cycle-Tempo), 32857 kW (GSP)
    High-pressure turbine
    • Inlet air temperature = 1152.57oC (Cycle-Tempo), 1152.56oC (GSP)
    • 59. Inlet air pressure = 23.59 bar (Cycle-Tempo), 23.59 bar (GSP)
    • 60. Outlet air temperature = 916.43oC (Cycle-Tempo), 915.84oC (GSP)
    • 61. Outlet air pressure = 9.545 bar (Cycle-Tempo), 9.531 bar (GSP)
    • 62. Power output = 32954 kW (Cycle-Tempo), 32857 kW (GSP)
    Intermediate-pressure turbine
    • Outlet air temperature = 736.26oC (Cycle-Tempo), 735.28oC (GSP)
    • 63. Outlet air pressure = 4.301 bar (Cycle-Tempo), 4.290 bar (GSP)
    • 64. Power output = 24458 kW (Cycle-Tempo), 24365 kW (GSP)
    Free-power turbine
    • Outlet air temperature = 460.50oC (Cycle-Tempo), 459.74oC (GSP)
    • 65. Outlet air pressure = 1.013 bar (Cycle-Tempo), 1.014 bar (GSP)
    • 66. Power output = 35937 kW (Cycle-Tempo), 35660 kW (GSP)
    No difference as large as 1%
  • 67. Design-Point and Off-Design Operations in GSP
    Processes in gas turbine components
    • Determined by relations among parameters defined by component maps and thermodynamic equations
    • 68. Parameters include air or gas properties and engine operating parameters, such as rotor speeds and efficiencies
    Design-point operation
    • Calculated from user specified design point data
    • 69. Component maps are not used, but instead, scale factors are calculated for scaling of the maps during subsequent off-design calculations
    • 70. Is always necessary before off-design simulations
    Off-design operation
    • Includes steady state and transient calculations
    • 71. Uses the design point as a reference point
    • 72. Operating conditions specified in many ways, such as fuel flow or control-system power setting, compressor bleed variation, and turbine power or torque variation
    Steady-state operation
    • A fully stabilized condition of gas turbine at a specific off-design condition
    Transient operation
    • Represents engine responses to variations in time of one or more operating conditions
    • 73. Transient effects included in GSP are rotor inertia, volume, heat soakage, and control system dynamics effects
    • 74. Rotor inertia, directly affecting rotor speed acceleration rates, usually is the dominating factor
  • Gas Turbine Engine Component Maps
    Off-design component characteristics are stored in component maps, such as compressor and turbine maps.
    Component characteristics generally defined by the following five parameters:
    • corrected mass flow (Wc)
    • 75. corrected rotational speed (Nc)
    • 76. pressure ratio (PR)
    • 77. component efficiency (η)
    • 78. Reynolds index
    • 79. Component maps
    • 80. Off-design performance is defined relativeto the design point and scaled proportionally
    • 81. Pressure ratio and corrected mass flow are often used as map parameters
    • 82. Three map input parameters are used to define the map operating point
    • 83. Both steady state and transient simulation results can be plotted in component maps to assess component performance, such as compressor stall margin
    • 84. For small differences (<25%), scaling usually does not add large errors; however, scaling for large difference will introduce large error margins
    • 85. Component maps for specific engines are hard to obtain
    • 86. Generic component maps, obtained from geometrically similar components, are typically used in gas turbine engine modeling and simulation
  • Unscaled Generic Compressor Map(General Electric J85 Gas Turbine Engine)
    The red line represents the compressor surge line
  • 87. Unscaled Generic Turbine Map(General Electric J85 Gas Turbine Engine)
  • 88. “Beta” Parameter in Component Maps
    • The constant speedcurves in a compressor or turbine map can be nearly vertical or nearly horizontal, and this causesnumerical problems.
    A “beta”parameter is typically used In compressor and turbine maps
    • To avoid numerical convergence problems during iterations toward operating point solutions
    • 89. representing a relation between pressure ratio and corrected mass flow
    • 90. constantbeta lines are virtually perpendicular to the constant corrected speed curves in themaps
    • 91. are equidistant, ranging between 0 and 1
    Two input parameters (i.e. beta parameter and speed parameter) can be used to find three output parameters (i.e., efficiency, pressure ratio, and corrected mass flow).
  • 92. Unscaled Generic Compressor Map(Beta Parameter Included)
  • 93. Unscaled Generic Turbine Map(Beta Parameter Included)
  • 94. A Steady-State Series Off-Design Simulation
    For dynamic modeling, the mass moments of inertia (MOI) of the engine components determine how quickly the angular velocities of the spools change as the engine operating conditions are altered.
    The values of the mass moments of inertia for gas turbine spools are very rare in open literature, especially for turbines with multiple spools.
    The following MOIs were assumed (Holsonback’s thesis):
    • MOI of HP spool = 620 kg-m2
    • 95. MOI of IP spool = 550 kg-m2
    • 96. MOI of FPT spool = 650 kg-m2
    The following rotational speeds were assumed (Holsonback’s thesis):
    • nominal rotational speed of HP = 10,000 rpm
    • 97. nominal rotational speed of IP = 7,500 rpm
    • 98. nominal rotational speed of FPT = 3,600 rpm
    • 99. A testing steady-state series off-design simulation was performed by investigating the relation between engine performance and fuel flow.
    • 100. A manual fuel flow control was applied over a wide operating range by sweeping the fuel flow rate from the design-point value of 2.07 kg/s to a value of 0.6 kg/s.
    • 101. Generic component maps were used to define the off-design characteristics.
  • MT30 Operating Lines in Scaled Component Maps (during An Off-Design Decreasing Fuel Flow Sweep)
    IPC
    HPC
    HPT
    IPT
  • 102. MT30 Operating Lines in Scaled Free-Power Turbine Map (during An Off-Design Decreasing Fuel Flow Sweep)
  • 103. A Transient Off-Design Simulation
    Input parameters are specified as functions of time, and the engine response to that input changes is then calculated.
    A testing transient simulation was carried out by using a manual fuel flow control to input an assumed time-dependent fuel flow rate (shown in the following figure).
  • 104. Predicted MT30 Engine Transient Parameters
    Specific Fuel Consumption
    Airflow Rate
    High-Pressure Turbine Inlet Temperature
    Free-Power Turbine Output
  • 105. GPS Licensing
    • Light Edition (LE)
    - used for non-commercial or evaluation purposes
    • Standard license
    - commercial single-user use of GSP Standard (LE + supplementary
    component library + STOVL component library)
    • Professional license
    - standard license with NLR support
    • Component Developers Package (CDP) license
    - enables the licensee to develop their own component models or extend
    simulation capabilities by making new component models inheriting from
    existing component models
    - vast amount of source code (Delphi, object pascal) will be distributed
    - with NLR support
    • Application Programmer’s Interface (API) license
    - to run engine simulations from in-house development environment
    (i.e., Matlab Simulink)
    - with NLR support
  • 106. Real-Time Gas Turbine Simulation
    The following are excerpted from “TERTS, a generic real-time gas turbine
    simulation environment”, authored by W.P.J. Visser, M.J. Broomhead, and
    J. van der Vorst, National Aerospace Laboratory NLR, February 2002.
    Real-time thermodynamic models require sophisticated methods to efficiently solve model equations on a real-time basis with sufficient speed.
    NLR has developed “Turbine Engine Real-Time Simulator” (TERTS), which is a generic real-time engine simulation environment for thermodynamic simulation of various gas turbine engine configurations.
    TERTS
    • A real-time tool for analyzing effects of malfunctions of control systems and sub-systems on performance
    • 107. Allows rapid adaptation to various configurations, rather than being dedicated to a specific engine
    • 108. Implemented in Matlab-Simulink by using graphical user interface to reflect component-based architecture of the gas turbine model
    • 109. Input is provided in files listing input variables, off-design component maps, control schedules, etc, and these files are accessed by any text file editor
    • 110. Uses scalable maps, control functions and dimensionless parameters, for generic component models
    • 111. Calculations performed on component level, using relations between component entry and exit gas properties based on component maps and thermodynamic equations
    • 112. All components modeled using GSP algorithms, except for turbine, which employs:
    - a simplified efficiency model based on a parabolic function of the loading parameter ΔH/U2
    - a rotor speed independent flow capacity map (function of pressure ratio only)
    • Higher fidelity can be achieved at cost of execution speed
    • 113. Model inaccuracy of the current system is well within 5%
  • The following three slides summarize component-wise gas turbine modeling in Virtual Test Bed (VTB) and model validation
    carried out by University of South Carolina
  • 114. 29
    Component-wise Gas Turbine VTB Model
    Gas Turbine
    Gas Turbine
    Simple-cycle
    2-shaft
    2 Stage compressor
    Intercooler
    Combustor
    Power Turbine
    Power turbine shaft speed feedback regulates fuel flow
    Six-phase
    Synchronous
    Generator
    Fuel Supply
    Heat
    Exchanger
    Combustor
    Low
    Pressure
    Compressor
    High
    Pressure
    Compressor
    Thermal
    Sink
    Note : compressors and turbines are characteristic curve based model.
    Power
    Turbine
    Gas Generator
    Turbine
    Intercooler
    Inlet Air
    Controllable
    resistive Load
    Starter
    Motor
  • 115. Validation of VTB Gas Turbine Model
    Compare a single shaft VTB model results with GasTurb commercial simulation software
    Boundary conditions for the VTB model match those for GasTurb
    Compressor inlet conditions
    Air bleed
    Design point of shaft speed
    Etc.
    Results were compared
    Pressures and temperatures at the compressor exit port
    Turbine inlet/outlet ports
    Shaft power
    Compressor Map
    Turbine Map
    VTB
    Gasturb
    Fuel
    Combustor
    Component maps employed by GasTurb
    Bleeding
    design point (N = 11427rpm, Mass flow rate 21.018 kg/s).
    compressor
    Turbine
    inlet
    Note : Characteristic curves near design point were extracted and put into VTB model
  • 116. Validation Results Comparison
    Design Point
    Compressor
    Outlet pressure error 2%,
    Outlet temperature error 9%
    Error caused by the assumption of ideal compression.
    Turbine
    Outlet pressure error 4%
    Outlet temperature error 8%
    Shaft power error 4%
    Note: GasTurb uses Generic fuel, while VTB assumes methane for these comparisons, we adjust the methane flow rate to match the compressor exhaust temperature.
    Off-Design Point
    Off-design validation
    Same engine settings.
    Different operating point.
    N = 9999 rpm - 10% below design point.
    Compressor
    Outlet temperature consistent with GasTurb
    Outlet pressure error 42%
    Error caused by the modeling method of the characteristic curve
    Turbine
    Outlet temperature error 15%
    Outlet pressure error 9%
    Shaft power error 8%

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