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Jet Engine Operation As An Integrated System INME5702 Class 13

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Agenda for Class 13

- Develop the Model for the Two-Spool Turbojet.

Two-Spool Turbojet – Model Schematic

Internal

Shaft

External

Shaft

Front

Compressor

(LPC)

Rear

Turbine

(LPT)

Internal

Compressor

(HPC)

Internal

Turbine

(HPT)

Inlet

Nozzle

*

Burner

*

4

3

*

8

0

2.5

4.5

5

2

*

~ Choked Flow

Blue ~ Added to SSTJ

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.

Air Velocity Out

Air Velocity In

N

INPUT SHAFT TORQUE

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.

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.

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

0

2.5

4.5

5

2

*

~ Choked Flow

Blue ~ Added to SSTJ

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 ?

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 ).

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 ).

Consider the Control Volumes That Defined Constraints for the SSTJ

- Has anything changed ( other than station numbering ) ?
- The answer is “No.”
- 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.

Consider the Control Volumes That Defined Constraints for the SSTJ

- Has anything changed ( other than station numbering ) ?
- The answer is “No.”
- 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 ).

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 ).

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

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

Combine Choked-Flow Equation with Turbine Efficiency To Get Turbine Expansion Ratio as f ( A8/A45 )

*

*

*

Low Spool Nomograph # 1

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

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

Compressor / Turbine Energy Balance Relates Compressor Work to Turbine Expansion Ratio

*

*

*

Low Spool Nomograph # 2

Compare Analogous Relationships for High and Low Spools

Compressor – Turbine Work Balance

Any difference in the form of these equations ?

Low Spool

High Spool

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

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

LPT Inlet Temperature Depends on Both HPT Efficiency and HPT Expansion Ratio

Low Spool Nomograph # 2a

Compressor Efficiency Relates Compressor Work to Compressor Pressure Ratio

Compressor Efficiency Relates Compressor Work to Compressor Pressure Ratio

Low Spool Nomograph # 3

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

Continuity Equation Relates Compressor Pressure Ratio to Compressor Inlet Corrected Flow

Low Spool Nomograph # 4

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.

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