2010 ESRDC Team Meeting

Operation and Modeling of Turbogenerators

Hsing-Pang LiuCenter for Electromechanics, University of Texas at Austin

Ruixian FangDepartment of Mechanical Engineering, University of South Carolina

June 3, 2010

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.

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

Commercial Gas Turbine Software Identified

• Gas Turbine Simulation Program “GSP”o Developed by Netherlands National Aerospace Laboratory NLRo Any gas turbine configurationo Steady-state and transient off-design simulationso GSP LE (Light Edition) downloaded for evaluation

• “GasTurb 11” o Developed by Dr. Joachim Kurzke (retired from Germany’s aircraft engine manufacturer MTU Aero Engines)o Simulates most common types of gas turbines for propulsion and for power generationo Simulates transient operation of gas turbineso Component maps offered in GasTurb are all taken from open literatureo Supports modeling of engines based on a limited amount of informationo Entry -level version downloaded for evaluation

• Numerical Propulsion System Simulation “NPSS” o Originally developed by NASA Glenn Research Center and its industrial/government partners for military jet

engine applications and space transportation o A consortium was later created to ensure continued development and enhancemento Latest version of NPSS 2.2.1 has been released for commercial distributiono Steady-state and transient off-design performance predictiono NIST (National Institute of Standards and Technology) compliant thermodynamic gas-properties packageo Evaluation edition with basic functionality downloaded for evaluation

Commercial Gas Turbine Software Identified(Continued)

• “VisSim Gas Turbine Simulator”o Developed by Visual Solutions Inc.o Steady-state and transient behavioro Downloaded for evaluation

• “GT PRO” o Developed by THERMOFLOWo Gas turbine combined cycle design program (mainly for gas turbine power plants)

• “GPAL Gas Turbine Simulators” o Developed by Gas Path Analysis Limitedo Single-shaft gas turbine (used in power generator)o Two-shaft gas turbine operating with a free power turbine (used in mechanical drive applications)

• “Flowmaster V7.7 Gas Turbine” o Developed by Flowmastero Design and simulation of gas turbine thermo-fluid systems

Gas Turbine Simulation Program “GSP”

• Historyo Initiated at Aerospace Department of Delft Technical University (in 1986) where

NASA's DYNGEN program was used for jet and turbofan engine simulationso First version of GSP developed by inheriting features from DYNGEN, combined

with improved stability and speed of numerical iteration processeso Implemented in object-oriented Borland Delphi environment in 1996o Now has an user-friendly drag&drop interface on Windows

• Modeling Approacho Zero-dimensional modeling of processes in different gas turbine components with

aero-thermodynamic relations and steady state characteristics (component maps)o Air and gas properties thermodynamically averaged over the flow cross-sectional

areas at inlet and exit of each component moduleo A pre-defined design point is calculated first from a set of design point datao 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

o 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”

• 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.

To date, GSP has been used for simulation of a large number of gas turbine engines including

These models have been developed at National Aerospace Laboratory NLR and some of them include proprietary data

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

Gas Turbine Engine Baseline Model (Used for Software Evaluation)

• Gas turbine engine chosen for evaluationo Rolls-Royce MT30 (MT stands for Marine Trent) gas turbine engineo Selected by US Navy to power IPS EDM, DDG 1000, and Littoral Combat Ship

(LCS)o Selected by UK MOD to power Royal Navy’s future all-electric aircraft carriero 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)

o 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 simulationo Predict steady-state performance at engine’s design pointo Compare results predicted by “Cycle-Tempo“ and “GSP”o 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

o 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

o Educated guesses and multiple iterations required

Rolls-Royce MT30 Gas Turbine Engine

Parameter Value Unit

Nominal Power 36.0 [MW]

Overall Pressure Ratio 24  

FPT Rated Speed 3,600 [rpm]

Specific Fuel Consumption 0.207 [kg/kW-hr]

Heat Rate (LHV) 8480 [Btu/kW-hr]

Thermal Efficiency 40.2%  

Exhaust Mass Flow 113 [kg/s]

Exhaust Temperature 466 [deg C]

IPC 8 stages

HPC 6 stages

HPT 1 stages

IPT 1 stages

FPT 4 stages

MT30 Steady-State Performance at Design Point(Predicted by Cycle-Tempo)

Pm = 35936.76 kW

i = 90 %

Pm = 24458.41 kW

i = 87 %

Pm = 32954.45 kW

i = 87 %

P = -32944.09 kW

i = 86 %

P = -24448.00 kW

i = 85 %

24.32 15.00

-1715.75 2.070 88

1.013 460.50

-446.68 113.00077

4.301 736.26

-128.65 113.00066

9.545 916.43

87.79 113.00055

23.59 1152.57

379.42 113.000

44

24.32 509.25

418.52 110.930

33

5.790 231.05

121.54 110.930 22

1.013 15.00

-98.85 110.93011

9

8

7

6

5

4

3

2

1

p T

h m

p = Pressure [bar]

T = Temperature [°C]

h = Enthalpy [kJ/kg]

m = Mass f low [kg/s]

P = Pow er [kW]

i = Isentropic eff iciency [%]

Pm = Mechanical Pow er [kW]

MT30 Steady-State Performance at Design Point(Predicted by GSP)

TT1 PT1 W1 TT21 PT21 DHW_c1 Eta_c1[K] [bar] [kg/s] [K] [bar] [kW] [-]

288.15 1.01325 110.93 504.6554 5.791433 24364.74 0.85

TT31 PT31 DHW_c Eta_c TT51 PT51 W51[K] [bar] [kW] [-] [K] [bar] [kg/s]

783.6095 24.32401871 32857.34 0.86 1425.713 23.5943 113

TT61 PT61 DHW_t Eta_t TT71 PT71 DHW_t1 Eta_t1[K] [bar] [kW] [-] [K] [bar] [kW] [-]

1188.991 9.530760702 32857.31 0.87 1008.428 4.28978 24364.74 0.87

TT81 PT81 DHW_t2 Eta_t2 TT9 PT9 W9 FN[K] [bar] [kW] [-] [K] [bar] [kg/s] [kN]

732.886 1.013586168 35660 0.9 732.886 1.013586 113 1.334664

Comparison of Predicted Component Parameters

• Intermediate-pressure compressoro Outlet air temperature = 231.05oC (Cycle-Tempo), 231.51oC (GSP)o Outlet air pressure = 5.79 bar (Cycle-Tempo), 5.79 bar (GSP)o Power input = 24448 kW (Cycle-Tempo), 24365 kW (GSP)

• High-pressure compressoro Outlet air temperature = 509.25oC (Cycle-Tempo), 510.46oC (GSP)o Outlet air pressure = 24.32 bar (Cycle-Tempo), 24.32 bar (GSP)o Power input = 32944 kW (Cycle-Tempo), 32857 kW (GSP)

• High-pressure turbineo Inlet air temperature = 1152.57oC (Cycle-Tempo), 1152.56oC (GSP)o Inlet air pressure = 23.59 bar (Cycle-Tempo), 23.59 bar (GSP)o Outlet air temperature = 916.43oC (Cycle-Tempo), 915.84oC (GSP)o Outlet air pressure = 9.545 bar (Cycle-Tempo), 9.531 bar (GSP)o Power output = 32954 kW (Cycle-Tempo), 32857 kW (GSP)

• Intermediate-pressure turbineo Outlet air temperature = 736.26oC (Cycle-Tempo), 735.28oC (GSP)o Outlet air pressure = 4.301 bar (Cycle-Tempo), 4.290 bar (GSP)o Power output = 24458 kW (Cycle-Tempo), 24365 kW (GSP)

• Free-power turbineo Outlet air temperature = 460.50oC (Cycle-Tempo), 459.74oC (GSP)o Outlet air pressure = 1.013 bar (Cycle-Tempo), 1.014 bar (GSP)o Power output = 35937 kW (Cycle-Tempo), 35660 kW (GSP)

No difference as large as 1%

Design-Point and Off-Design Operations in GSP

• Processes in gas turbine componentso Determined by relations among parameters defined by component maps and

thermodynamic equationso Parameters include air or gas properties and engine operating parameters, such as rotor

speeds and efficiencies

• Design-point operationo Calculated from user specified design point datao Component maps are not used, but instead, scale factors are calculated for scaling of the

maps during subsequent off-design calculationso Is always necessary before off-design simulations

• Off-design operationo Includes steady state and transient calculationso Uses the design point as a reference pointo 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 operationo A fully stabilized condition of gas turbine at a specific off-design condition

• Transient operationo Represents engine responses to variations in time of one or more operating conditionso Transient effects included in GSP are rotor inertia, volume, heat soakage, and control

system dynamics effectso 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:o corrected mass flow (Wc)

o corrected rotational speed (Nc)

o pressure ratio (PR)o component efficiency (η)o Reynolds index

• Component mapso Off-design performance is defined relative to the design point and scaled proportionallyo Pressure ratio and corrected mass flow are often used as map parameterso Three map input parameters are used to define the map operating pointo Both steady state and transient simulation results can be plotted in component maps to

assess component performance, such as compressor stall margino For small differences (<25%), scaling usually does not add large errors; however, scaling for

large difference will introduce large error marginso Component maps for specific engines are hard to obtaino 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

Unscaled Generic Turbine Map(General Electric J85 Gas Turbine Engine)

“Beta” Parameter in Component Maps

• The constant speed curves in a compressor or turbine map can be nearly vertical or nearly horizontal, and this causes numerical problems.

• A “beta” parameter is typically used In compressor and turbine maps o To avoid numerical convergence problems during iterations toward operating

point solutionso representing a relation between pressure ratio and corrected mass flowo constant beta lines are virtually perpendicular to the constant corrected speed

curves in the mapso 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).

Unscaled Generic Compressor Map(Beta Parameter Included)

Unscaled Generic Turbine Map(Beta Parameter Included)

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):o MOI of HP spool = 620 kg-m2

o MOI of IP spool = 550 kg-m2

o MOI of FPT spool = 650 kg-m2

• The following rotational speeds were assumed (Holsonback’s thesis):o nominal rotational speed of HP = 10,000 rpmo nominal rotational speed of IP = 7,500 rpmo nominal rotational speed of FPT = 3,600 rpm

• A testing steady-state series off-design simulation was performed by investigating the relation between engine performance and fuel flow.

• 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.

• 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

MT30 Operating Lines in Scaled Free-Power Turbine Map (during An Off-Design Decreasing Fuel Flow Sweep)

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).

Predicted MT30 Engine Transient Parameters

Specific Fuel Consumption Airflow Rate

High-Pressure Turbine Inlet Temperature Free-Power Turbine Output

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

Real-Time Gas Turbine Simulation

• 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 o A real-time tool for analyzing effects of malfunctions of control systems and sub-systems on

performanceo Allows rapid adaptation to various configurations, rather than being dedicated to a specific engineo Implemented in Matlab-Simulink by using graphical user interface to reflect component-based

architecture of the gas turbine modelo Input is provided in files listing input variables, off-design component maps, control schedules, etc, and

these files are accessed by any text file editoro Uses scalable maps, control functions and dimensionless parameters, for generic component models o Calculations performed on component level, using relations between component entry and exit gas

properties based on component maps and thermodynamic equationso 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)

o Higher fidelity can be achieved at cost of execution speedo Model inaccuracy of the current system is well within 5%

The following are excerpted from “TERTS, a generic real-time gas turbinesimulation environment”, authored by W.P.J. Visser, M.J. Broomhead, andJ. van der Vorst, National Aerospace Laboratory NLR, February 2002.

The following three slides summarize component-wise gas turbine modeling in Virtual Test Bed (VTB) and model validationcarried out by University of South Carolina

29

Component-wise Gas Turbine VTB Model

• Gas Turbine– Simple-cycle– 2-shaft– 2 Stage compressor– Intercooler– Combustor– Power Turbine– Power turbine shaft

speed feedback regulates fuel flow

Six-phaseSynchronousGenerator

Power Turbine

Gas GeneratorTurbine

Fuel Supply

Heat Exchanger

Intercooler

Inlet Air

ThermalSink

Combustor

StarterMotor

LowPressureCompressor

HighPressureCompressor

Controllableresistive Load

Gas Turbine

Note : compressors and turbines are characteristic curve based model.

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 Turbineinlet

Combustor

Fuel

Bleeding

Note : Characteristic curves near design point were extracted and put into VTB model

Compressor Map Turbine Map

design point (N = 11427rpm, Mass flow rate 21.018 kg/s).

Component maps employed by GasTurb

VTB Gasturb

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%