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Engine Performance Analysis
Transcript of Engine Performance Analysis
Engine Performance Analysis
© 2015 SIM University. All rights reserved.
• The basics of engine performance analysis
• The parameters and tools used in engine
performance analysis
© 2015 SIM University. All rights reserved.
Introduction
• Parametric cycle analysis:
– Independently selected input:
�Flight condition M0, T0, P0
�Design choices �c, Tt4, ec, et, etc.
– Determines �� = 1 −�
� ��
�
���� − 1 (a variable)
– Performance output: F/ṁ0, S, η, etc.
– Performance is determined at specific design flight conditions,
values and limits
– Input design or reference point
© 2015 SIM University. All rights reserved.
Introduction
• Consider performance of engine built with selected design point
• When installed, its performance varies
– flight conditions
– throttle settings
– limited by engine control system
• When input is changed, component design changes (not possible
with engine once built)
© 2015 SIM University. All rights reserved.
Limitations of Parametric Cycle Analysis
• Looks at how specific engine perform at conditions other than
design point (Off-design analysis)
• Engine built with selected design point
– Selected compressor pressure ratio �c
– corresponding turbine temperature ratio �� (essentially constant)
• �c is dependent on the throttle setting (Tt4) and flight condition (M0
and T0)
• Off-design analysis:
– Changing through the throttle and indirectly by changing flight
conditions
– Performance other than their design point
© 2015 SIM University. All rights reserved.
Engine Performance Analysis
© 2015 SIM University. All rights reserved.
Variable Parametric
cycle
Engine
performance
Flight condition (M0, T0, and P0) Independent Independent
Compressor pressure ratio �c
Independent Dependent
(on engine speed
and flight
conditions)
Main burner exit temperature Tt4 Independent Independent
(throttle input)
Turbine temperature ratio �� Dependent
(on flight
conditions, �c
,
and Tt4 )
Constant
Table 7-1 Comparison of Analysis Variables
Source: Page 438
“Elements of Propulsion: Gas Turbines and Rockets” by Jack D. Mattingly
Engine Performance Analysis
• Engine design point or reference point
– Specific set of input values that basic engine is designed to:
�Flight condition M0, T0, P0
�Design choices πc, Tt4, ��, ec, et, etc.
– Resulting F/ṁ0, TSFC are valid only for the given engine cycle
and values of Tt4, M0, T0, etc.
– Normal design point – Sea-level Static (SLS)
© 2015 SIM University. All rights reserved.
Design (Reference) Point
Low Pressure Spool (N1)
High Pressure Spool (N2)
© 2015 SIM University. All rights reserved.Source: Page 439
“Elements of Propulsion: Gas Turbines and Rockets” by Jack D. Mattingly
Twin-Spool Gas Turbine Engine
Subscript H denotes HP spool and L denotes LP spool
Table 7-2 Additional Temperature and Pressure Relationships
© 2015 SIM University. All rights reserved.Source: Page 439
“Elements of Propulsion: Gas Turbines and Rockets” by Jack D. Mattingly
Twin-Spool Gas Turbine Engine
• Fixed-Area Turbine (FAT) conventional turbo machine - choked
flow at
– Turbine inlet nozzles (HP turbine and LP turbine)
– Exhaust nozzle (core engine and fan duct, if separate)
• Unchanged from reference values:
– �� , ��, ���, �� , �� , ��, ��� , ���, ��� ,���
• Turbine cooling and leakage effects are neglected
• No power is removed from the turbine to drive accessories
• Constant �� and ��� , and�� and ��� that do not vary with power
setting
• The term 1 + � is considered as constant
© 2015 SIM University. All rights reserved.
Reference Values and Assumptions
• Impossible to test and record all operating conditions
• Dimensional analysis identifies correlating parameters that allow
engine performance to be analysed under different conditions
• Dimensionless pressure and temperature represented by δ and θ
• Corrected mass flow rate at engine station i
where i is the station number
© 2015 SIM University. All rights reserved.
Dimensional Analysis
© 2015 SIM University. All rights reserved.Source: Page 443
“Elements of Propulsion: Gas Turbines and Rockets” by Jack D. Mattingly
Table 7-3 Corrected Parameters
Corrected Parameters
Figure 7-2 Compressor Performance Map
• Steady operation above the surge line is
impossible
• Entering the region even momentarily is
dangerous to the gas turbine engine.
© 2015 SIM University. All rights reserved.Source: Page 444
“Elements of Propulsion: Gas Turbines and Rockets” by Jack D. Mattingly
Compressor and Fan Performance Map
Compressor stall may take one of two forms:
• High angle of attack (positive incidence) blade stall
– A front stage problem at low speeds
• Low AOA (negative incidence stall)
– Windmilling of blades
– Affects the rear stages at high speed
• Leads to blade vibration which can induce rapid destruction
© 2015 SIM University. All rights reserved.
Watch video on Compressor Stall
Compressor Stall
• Caused by excessive demand for compressor pressure rise
– Beyond blades’ handling capability
• Results in:
– Instantaneous breakdown of flow through the engine
– High pressure air in the combustion system is expelled forward
through the compressor
– ‘Loud’ bang’
– Resultant loss of engine thrust
© 2015 SIM University. All rights reserved.
Watch video on Compressor Surge
Compressor Surge
• Bleed valves to release air from
middle stages
• Multi-spool compressors
– Optimum speeds for different
spools
• Variable stator vanes, including the
inlet guide vanes to guide the airflow
at a desired angle
• Proper fuel scheduling to operate
within Compressor Performance Map
– Limiting excessive pressure ratio
during acceleration
© 2015 SIM University. All rights reserved.
Source: Page 29, “The Jet Engine” (1986) by
Rolls Royce plc,
Compressor Stall / Surge Prevention
Figure 7-3 Combustor Efficiency
© 2015 SIM University. All rights reserved.Source: Page 445
“Elements of Propulsion: Gas Turbines and Rockets” by Jack D. Mattingly
Combustor Performance Map
Figure 7-4 Combustor Efficiency
Burner Temperature Rise
Burner inlet pressure
© 2015 SIM University. All rights reserved.Source: Page 445
“Elements of Propulsion: Gas Turbines and Rockets” by Jack D. Mattingly
Combustor Performance Map
Figure 7-5 Turbine Flow Map
To achieve high
power to weight
ratio, flow
entering 1st stage
rotor is normally
supersonic. Thus,
sonic conditions
are present at the
minimum
passage area of
the inlet guide
vanes
© 2015 SIM University. All rights reserved.Source: Page 446
“Elements of Propulsion: Gas Turbines and Rockets” by Jack D. Mattingly
Turbine Performance Map
Figure 7-6 Turbine Efficiency Map
Turbine efficiency
assumed as constant
during performance
analysis
© 2015 SIM University. All rights reserved.Source: Page 447
“Elements of Propulsion: Gas Turbines and Rockets” by Jack D. Mattingly
Turbine Performance Map
© 2015 SIM University. All rights reserved.
Performance Analysis Variables for Single-Spool Turbojet Engine
Source: Page 465
“Elements of Propulsion: Gas Turbines and Rockets” by Jack D. Mattingly
Single-Spool Turbojet w/o Afterburner
© 2015 SIM University. All rights reserved.Source: Page 467 - 469
“Elements of Propulsion: Gas Turbines and Rockets” by Jack D. Mattingly
Single-Spool Turbojet w/o Afterburner
© 2015 SIM University. All rights reserved.Source: Page 469
“Elements of Propulsion: Gas Turbines and Rockets” by Jack D. Mattingly
Single-Spool Turbojet w/o Afterburner
Adapted from R-1, Example 8.4
© 2015 SIM University. All rights reserved.Source: Page 473
“Elements of Propulsion: Gas Turbines and Rockets” by Jack D. Mattingly
Single-Spool Turbojet w/o Afterburner
Adapted from R-1, Example 8.4
© 2015 SIM University. All rights reserved.Source: Page 474
“Elements of Propulsion: Gas Turbines and Rockets” by Jack D. Mattingly
Single-Spool Turbojet w/o Afterburner
Adapted from R-1, Example 8.4
Altitude = 20 kft
Mach number = 0.8
• As thrust is reduced from 100%
(reading graph from right to
left),
o ηP increases
o ηT decreases
o ηO increases to optimum at
40% power setting
o TSFC decreases until about
40% of maximum thrust, then
increases
• Effect due to increase in ηP
dominating the reduction of ηT
at throttle settings down till
40%.
© 2015 SIM University. All rights reserved.
Turbojet Performance at Partial Throttle
Source: Page 476
“Elements of Propulsion: Gas Turbines and Rockets” by Jack D. Mattingly
Single-Spool Turbojet w/o Afterburner
• The basics of engine performance analysis
• The need for design point and dimensional
analysis
• Plot and critique component performance maps
© 2015 SIM University. All rights reserved.
Summary
• Review the component performance maps of a
compressor and turbine:
– Explain the compressor stall/surge line.
– Discuss the rationale that the flow at the
turbine inlet nozzle is assumed to be choked.
© 2015 SIM University. All rights reserved.
Reflection Question