Jet Engine Operation As An Integrated System INME5702 Class 13

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Jet Engine OperationAs An Integrated
SystemINME5702Class 13
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Agenda for Class 13

• Develop the Model for the Two-Spool Turbojet.

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Two-Spool Turbojet Model Schematic
Internal Shaft
External Shaft
Front Compressor (LPC)
Rear Turbine (LPT)
Internal Compressor (HPC)
Internal Turbine (HPT)
Inlet
Nozzle

2

Choked Flow
Blue Added to SSTJ
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Twin-Spool Turbojet h-s Diagram
h
s
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Why Two Spools ? Primary reason is to optimize
the compression process. Compression is the most
difficult aerodynamic challenge in the gas
turbine engine. The same pressure change must
occur over many more stages in compression than
in turbine expansion due to the increased risks
of boundary layer build-up and flow separation in
the compressor.
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Why Two Spools ?
Compressor performance is dependent on (among
other parameters) the ratio of axial velocity to
tangential velocity in the stages of the
compressor Vx / U Tangential velocity, U, is
proportional to wheel speed, N. Performance can
be improved across the stages of a compressor by
limiting the variation of Vx/U. Splitting the
compressor into two separate machines allows
improved control over the range of Vx/U within
each compressor ( 2 values of N available rather
than 1 ). The result is improved compression
performance.
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• What Are The Differences Between The Single-Spool
  and Two-Spool Turbojet ?
• There is no new physics, i.e., no new
  fundamental relationships.
• Two new components are added, the LPC and the
  LPT.
• Each has its own efficiency.
• One new choking plane is added between the
  turbines ( Station 4.5 ).
• The HPT continues to operate between choked
  planes,
• now A4 and A45 instead of A4 and A8.
• The LPT also operates between choked planes, A45
  and A8.
• The HPC inlet is now station 2.5 instead of 2.0.

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High-Pressure Spool Nomograph Equations
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Consider the Control Volumes That Defined
Constraints for the SSTJ Has anything changed (
other than station numbering ) ?
Internal Shaft
External Shaft
Front Compressor (LPC)
Rear Turbine (LPT)
Internal Turbine (HPT)
Internal Compressor (HPC)
Inlet
Nozzle

Burner

4
3
8

2.5
0
5
4.5
2

Choked Flow
Blue Added to SSTJ
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• Consider the Control Volumes That Defined
  Constraints for the SSTJ
• Has anything changed ( other than station
  numbering ) ?
• The answer is No.
• The High-Pressure Spool of the TSTJ matches
  using the same principles as the SSTJ. Can
  you state these principles ?

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• Consider the Control Volumes That Defined
  Constraints for the SSTJ
• Has anything changed ( other than station
  numbering ) ?
• The answer is No.
• The High-Pressure Spool of the TSTJ matches
  using the same principles as the SSTJ. Can
  you state these principles ?
• Turbine area ratio determines turbine expansion
  ratio
• ( turbine efficiency has a second-order
  effect ).

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• Consider the Control Volumes That Defined
  Constraints for the SSTJ
• Has anything changed ( other than station
  numbering ) ?
• The answer is No.
• The High-Pressure Spool of the TSTJ matches
  using the same principles as the SSTJ. Can
  you state these principles ?
• Turbine area ratio determines turbine expansion
  ratio
• ( turbine efficiency has a second-order
  effect ).
• Turbine expansion ratio and turbine inlet
  corrected temperature determine compressor
  corrected work
• ( since compressor work equals turbine work
  ).

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• Consider the Control Volumes That Defined
  Constraints for the SSTJ
• Has anything changed ( other than station
  numbering ) ?
• The answer is No.
• The High-Pressure Spool of the TSTJ matches
  using the same principles as the SSTJ. Can
  you state these principles ?
• Turbine area ratio determines turbine expansion
  ratio
• ( turbine efficiency has a second-order
  effect ).
• Turbine expansion ratio and turbine inlet
  corrected temperature determine compressor
  corrected work
• ( since compressor work equals turbine work
  ).
• Compressor corrected work and compressor
  efficiency determine compressor pressure ratio.

14

• Consider the Control Volumes That Defined
  Constraints for the SSTJ
• Has anything changed ( other than station
  numbering ) ?
• The answer is No.
• The High-Pressure Spool of the TSTJ matches
  using the same principles as the SSTJ. Can
  you state these principles ?
• Turbine area ratio determines turbine expansion
  ratio
• ( turbine efficiency has a second-order
  effect ).
• Turbine expansion ratio and turbine inlet
  corrected temperature determine compressor
  corrected work
• ( since compressor work equals turbine work
  ).
• Compressor corrected work and compressor
  efficiency determine compressor pressure ratio.
• Compressor pressure ratio and turbine inlet
  corrected temperature determine compressor inlet
  corrected flow
• ( with FP4, (DP/P)Burner, and A4 as
  parameters ).

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These Principles Describe the Nomograph for the
SSTJ ( or the High-Pressure Spool of the TSTJ )

• Turbine area ratio determines turbine expansion
  ratio
• ( turbine efficiency has a second-order
  effect ).
• Turbine expansion ratio and turbine inlet
  corrected temperature determine compressor
  corrected work
• ( since compressor work equals turbine work
  ).
• Compressor corrected work and compressor
  efficiency determine compressor pressure ratio.
• Compressor pressure ratio and turbine inlet
  corrected temperature determine compressor inlet
  corrected flow
• ( with FP4, (DP/P)Burner, and A4 as
  parameters ).

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TSTJ High-Spool Matching With Nomographs
4. WC25 - FP4 Continuity
2. HPC / HPT Energy Balance
Finish
hHPT
3. HPC Efficiency
hHPT
1. Choked FP4, FP45, HPT Efficiency
Start
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• Low-Pressure Spool Nomograph Equations
• Turbine Expansion Ratio Turbine Area Ratio
• Choked Inlet/Exit and Turbine Efficiency
• Compressor Turbine Energy Balance
• Compressor Pressure Ratio Input Work
• Compressor Efficiency
• Compressor Pressure Ratio Corrected Flow
• Continuity

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Combine Choked-Flow Equation with Turbine
Efficiency To Get Turbine Expansion Ratio as f (
A8/A45 )
Low Spool Nomograph 1
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Compare Analogous Relationships for High and Low
Spools
Expansion Ratio Area Ratio Relationship
Any difference in the form of these equations ?
Low Spool
High Spool
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Compare Analogous Relationships for High and Low
Spools
Expansion Ratio Area Ratio Relationship
Any difference in the form of these equations ?
Low Spool
High Spool
Constants
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Compressor / Turbine Energy Balance Relates
Compressor Work to Turbine Expansion Ratio
Low Spool Nomograph 2
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Compare Analogous Relationships for High and Low
Spools
Compressor Turbine Work Balance
Any difference in the form of these equations ?
Low Spool
High Spool
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Compare Analogous Relationships for High and Low
Spools
Compressor Turbine Work Balance
What about T45/Q25 ?
Low Spool
High Spool
Constants
Specified as the power setting
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Compare Analogous Relationships for High and Low
Spools
Compressor Turbine Work Balance
Inlet temperature to the LPT depends on HPT
output !!!
Low Spool
High Spool
Constants
Specified as the power setting
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LPT Inlet Temperature Depends on Both HPT
Efficiency and HPT Expansion Ratio
Low Spool Nomograph 2a
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Compressor Efficiency Relates Compressor Work to
Compressor Pressure Ratio
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Compressor Efficiency Relates Compressor Work to
Compressor Pressure Ratio
Low Spool Nomograph 3
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Compare Analogous Relationships for High and Low
Spools
Compressor Pressure Ratio Input Work
Relationship
Any difference in the form of these equations ?
Low Spool
High Spool
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Continuity Equation Relates Compressor Pressure
Ratio to Compressor Inlet Corrected Flow
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Continuity Equation Relates Compressor Pressure
Ratio to Compressor Inlet Corrected Flow
Low Spool Nomograph 4
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Compare Analogous Relationships for High and Low
Spools
Low Spool
High Spool
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Compare Analogous Relationships for High and Low
Spools
Low Spool LPC Pressure Ratio is related to LPC
Inlet Corrected Flow by LPC Efficiency and HPC
Inlet Corrected Flow.
High Spool HPC Pressure Ratio is related to HPC
Inlet Corrected Flow by T4/Q25, FP4, A4, and
(DP/P)Burner.