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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
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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.
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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
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Originally developed by NASA Glenn Research Center and its industrial/government partners for military jet engine applications and space transportation
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A consortium was later created to ensure continued development and enhancement
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Latest version of NPSS 2.2.1 has been released for commercial distribution
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Steady-state and transient off-design performance prediction
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NIST (National Institute of Standards and Technology) compliant thermodynamic gas-properties package
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Evaluation edition with basic functionality downloaded for evaluation
Commercial Gas Turbine Software Identified(Continued)
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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
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First version of GSP developed by inheriting features from DYNGEN, combined with improved stability and speed of numerical iteration processes
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Implemented in object-oriented Borland Delphi environment in 1996
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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)
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Air and gas properties thermodynamically averaged over the flow cross-sectional areas at inlet and exit of each component module
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A pre-defined design point is calculated first from a set of design point data
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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
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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
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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
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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
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Selected by US Navy to power IPS EDM, DDG 1000, and Littoral Combat Ship (LCS)
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Selected by UK MOD to power Royal Navy’s future all-electric aircraft carrier
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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)
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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
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Compare results predicted by “Cycle-Tempo“ and “GSP”
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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
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Educated guesses and multiple iterations required
Rolls-Royce MT30 Gas Turbine Engine
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MT30 Steady-State Performance at Design Point(Predicted by Cycle-Tempo)
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MT30 Steady-State Performance at Design Point(Predicted by GSP)
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Comparison of Predicted Component Parameters Intermediate-pressure compressor
Outlet air temperature = 231.05oC (Cycle-Tempo), 231.51oC (GSP)
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Outlet air pressure = 5.79 bar (Cycle-Tempo), 5.79 bar (GSP)
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Power input = 24448 kW (Cycle-Tempo), 24365 kW (GSP)
High-pressure compressor
Outlet air temperature = 509.25oC (Cycle-Tempo), 510.46oC (GSP)
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Outlet air pressure = 24.32 bar (Cycle-Tempo), 24.32 bar (GSP)
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Power input = 32944 kW (Cycle-Tempo), 32857 kW (GSP)
High-pressure turbine
Inlet air temperature = 1152.57oC (Cycle-Tempo), 1152.56oC (GSP)
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Inlet air pressure = 23.59 bar (Cycle-Tempo), 23.59 bar (GSP)
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Outlet air temperature = 916.43oC (Cycle-Tempo), 915.84oC (GSP)
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Outlet air pressure = 9.545 bar (Cycle-Tempo), 9.531 bar (GSP)
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Power output = 32954 kW (Cycle-Tempo), 32857 kW (GSP)
Intermediate-pressure turbine
Outlet air temperature = 736.26oC (Cycle-Tempo), 735.28oC (GSP)
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Outlet air pressure = 4.301 bar (Cycle-Tempo), 4.290 bar (GSP)
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Power output = 24458 kW (Cycle-Tempo), 24365 kW (GSP)
Free-power turbine
Outlet air temperature = 460.50oC (Cycle-Tempo), 459.74oC (GSP)
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Outlet air pressure = 1.013 bar (Cycle-Tempo), 1.014 bar (GSP)
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Power output = 35937 kW (Cycle-Tempo), 35660 kW (GSP)
No difference as large as 1%
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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
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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
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Component maps are not used, but instead, scale factors are calculated for scaling of the maps during subsequent off-design calculations
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Is always necessary before off-design simulations
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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
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Transient effects included in GSP are rotor inertia, volume, heat soakage, and control system dynamics effects
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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:
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Off-design performance is defined relativeto the design point and scaled proportionally
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Pressure ratio and corrected mass flow are often used as map parameters
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Three map input parameters are used to define the map operating point
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Both steady state and transient simulation results can be plotted in component maps to assess component performance, such as compressor stall margin
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For small differences (<25%), scaling usually does not add large errors; however, scaling for large difference will introduce large error margins
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Component maps for specific engines are hard to obtain
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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
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Unscaled Generic Turbine Map(General Electric J85 Gas Turbine Engine)
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).
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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):
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A testing steady-state series off-design simulation was performed by investigating the relation between engine performance and fuel flow.
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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.
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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
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MT30 Operating Lines in Scaled Free-Power Turbine Map (during An Off-Design Decreasing Fuel Flow Sweep)
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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).
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Predicted MT30 Engine Transient Parameters Specific Fuel Consumption Airflow Rate High-Pressure Turbine Inlet Temperature Free-Power Turbine Output
- 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
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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
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Allows rapid adaptation to various configurations, rather than being dedicated to a specific engine
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Implemented in Matlab-Simulink by using graphical user interface to reflect component-based architecture of the gas turbine model
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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
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Uses scalable maps, control functions and dimensionless parameters, for generic component models
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Calculations performed on component level, using relations between component entry and exit gas properties based on component maps and thermodynamic equations
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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
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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
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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
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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
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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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