1. Gas Turbine Theory and Construction

2. Introduction
Comprehend the thermodynamic processes occurring in a gas turbine
Comprehend the basic components of gas turbine engines and their basic operation
Comprehend the support systems associated with gas turbine engines

3. Background
Aircraft turbojet/turbofan engines are precursors to gas turbines
Installed for propulsion in:
FFG’s
DD’s
DDG’s
CG’s
M-1 tanks
Also used for electrical generation & auxiliary applications

4. Advantages of GTE’s Weight reduction of 70% Simplicity
Reduced manning requirements
Quicker response time
Faster Acceleration/deceleration
Modular replacement
Less vibrations
More economical

5. Disadvantages of GTE’s
Many parts under high stress
High pitched noise
Needs large quantities of air
Large quantities of hot exhaust (target)
Cannot be repaired in place

6. Brayton Cycle Unlike diesels, operate on STEADY-FLOW cycle
Open cycle, unheated engine
1-2: Compression
2-3: Combustion
3-4: Expansion through Turbine and Exhaust Nozzle
(4-1: Atmospheric Pressure)

7. Basic Components

8. Basic Components

9. Basic Components Compressor Combustion Chamber Turbine
Draws in air & compresses it
Combustion Chamber
Fuel pumped in and ignited to burn with compressed air
Turbine
Hot gases converted to work
Can drive compressor & external load
Air is drawn into the front of the compressor. Each succeeding stage is smaller increasing velocity (recall Bernoullis equation).
Between each rotating stage is a stationary stage or stator. The stator partially converts the high velocity to pressure and directs the air to the next set of rotating blades.
The rotor imparts velocity to the air (like a fan). Each stage consists of a rotor and stator and results in a pressure increase.
Air exits the compressor and enters the diffuser. Suddenly, the air moves from a narrow passage into a wide area. By bernoulli, the air loses velocity and expands in volume and increases pressure. Now, the air is slow moving and high pressure, usually about 19:1. Fuel is injected here and the mixture is ignited by a spark. The spark causes a rapid increase in the volume of the air an combustion gases (at constant pressure).
The combustion mixture goes rearward to a nozzle which directs the gas onto the turbine blades and accelerates the gases. The gases are now high velocity, high temperature, low pressure and are used to turn the turbine. The kinetic and thermal energy of the gases are transferred the turbine blades. The turbine is multistaged to remove as much of the energy from the gas as possible.

10. Basic Components Compressor Combustion Chamber Turbine
Draws in air & compresses it
Combustion Chamber
Fuel pumped in and ignited to burn with compressed air
Turbine
Hot gases converted to work
Can drive compressor & external load

11. Basic Components Compressor Combustion Chamber Turbine
Draws in air & compresses it
Combustion Chamber
Fuel pumped in and ignited to burn with compressed air
Turbine
Hot gases converted to work
Can drive compressor & external load

12. Compressor Supplies high pressure air for combustion process
Compressor types
Radial/centrifugal flow compressor
Axial flow compressor

13. Compressor Radial/centrifugal flow Axial flow
Adv: simple design, good for low compression ratios (5:1)
Disadv: Difficult to stage, less efficient
Axial flow
Good for high compression ratios (20:1)
Most commonly used
Radial flow or centrifugal compressor- compressor draws in the entering air at the hub of the impeller and accelerates it radially outward by centrifugal force through the impeller. Reasonably efficient for high pressure ratios developed in a single stage.
Axial flow- Rotor has fixed blades which force the air rearward much like an aircraft propeller. The stator directs the air rearward to the next stage. Very much like a turbine used in reverse. Used in multistage arrangements and pressure ratios increase with the number of stages.

14. Compressor Controlling Load on Compressor Compressor Stall
To ensure maximum efficiency and allow for flexibility, compressor can be split into HP & LP sections
Vane control: inlet vanes/nozzle angles can be varied to control air flow
Compressor Stall
Interruption of air flow due to turbulence

15. Use of Compressed Air Primary Air (30%) Secondary Air (65%)
Passes directly to combustor for combustion process
Secondary Air (65%)
Passes through holes in perforated inner shell & mixes with combustion gases
Film Cooling Air (5%)
Insulates/cools turbine blades

16. Combustion Chambers Where air & fuel are mixed, ignited, and burned
Spark plugs used to ignite fuel
Types
Can: for small, centrifugal compressors
Annular: for larger, axial compressors (LM 2500)
Can-annular: for really large turbines

17. Can Type- Individual liners and cases mounted around the engine each with its own fuel nozzle.

18. Annular type- Liner consists of an undivided circular shroud extending all the way around the outside of the turbine shaft housing. The dome of the liner has small slots and holes to admit primary air. There are also holes in the dome for the fuel nozzles to extend through into the combustion area. The combustion space is formed by the inner and outer liners. The inner liner prevents flame from contacting the turbine shaft housing.

19. Can-annular type- Designed to deal with split spool compressor
Can-annular type- Designed to deal with split spool compressor. Individual cans are placed inside an annular case. Combines the strength of annular design with the convenience of maintenance of the can. Also keeps high temperatures in the inner can.

20. Turbines
Consists of one or more stages designed to develop rotational energy
Uses sets of nozzles & blades
Turbines, like compressors, consist of stator and rotor elements. Stators prepare the mass flow for harnessing of power through the turbine rotor. The nozzles take the high pressure, high-energy mixture and give it velocity for driving the rotor. Also deflects the gases to a specific angle in the direction of the turbine wheel rotation.
Rotors consist of a shaft and bladed wheel. Turbine operates at high speed

21. Turbines Split Shaft Gas generator turbine drives compressor
Power turbine separate from gas generator turbine
Power turbine driven by exhaust from gas generator turbine
Power turbine drives power coupling

22. Single Shaft Efficiently operates at constant speeds
Used in GTGS (gas turbine generator systems)
Single shaft
Power coupling on same shaft as turbine
Same shaft drives rotor of compressor and power components
*Primarily used for electric power because of constant speed, regardless of load.

23. Single- Aircraft and electric power- constant speed independent of load

24. Split Shaft Best where speeds and loads vary Used in LM-2500
Power shaft is decoupled from compressor
Allows both to operate at efficient speeds (not the same)
*More suitable for main propulsion applications due to the fact that the gas generator turbine and power turbine operate near their most efficient speeds throughout a RANGE of load demands.

25. Split- allows the compressor to run at different speed that power turbine maximizing the efficiency of operation.

26. Accessory Drive Assembly
Purpose - Provides motive force for driving the accessories required for operation and control of engine
Attached Accessory Equipment
Fuel oil pump
Lube oil pump
Starter (pneumatic, electric, hydraulic)
Provides the space for mounting and the motive force for driving the accessories required for the operation and control of the engine
Discuss the following accessory equipment attached at the assembly:
Fuel oil pump
Lube oil pump
Starter (pneumatic, electric, hydraulic)

27. Gas Turbine Systems Air System Fuel System Lubrication System
Air intakes are located high up & multiple filters
Exhaust discharged out stacks
Fuel System
Uses either DFM or JP-5
Lubrication System
Supply bearings and gears with oil

28. Gas Turbine Systems Starting System Power Transmission System
To get compressor initially rotated, HP air used (can use electrical also)
Once at certain RPM, fuel injected and spark ignited
Power Transmission System
Reduction gears used to transfer torque
With split shaft, turbines can different speeds

29. Questions?