Gas Turbines

Question 1

Define a working fluid?

Answer 1

Any gas or liquid that can do work by expansion or flow, or can be compressed or made to flow.

Question 2

Define a turbine?

Answer 2

A bladed spool designed to rotate when acted on by a working fluid.

Question 3

Define a compressor?

Answer 3

A bladed spool designed to do work on a fluid when it is rotated.

Question 4

What is the function of a gas turbine?

Answer 4

Gas turbines convert heat energy into rotary motion for ships propulsion

Question 5

Propulsion configurations include:

Answer 5

IEP - integrated electric propulsion (type 45)

CODLAG - combination of diesel electric and gas

Question 6

What are the advantages of a gas turbine?

Answer 6

Allows the ship to get underway quickly
Ease of operation and emphasis on remote control
High power to weight ratio
Minimum ship borne maintenance
Lower man power requirement

Question 7

Describe the air intake system?

Answer 7

Air is drawn from the upper deck via the 3 stage filter, removing particle and moisture contamination.
There is also a manometric leg to ensure no unfiltered air enters the intake system.

Question 8

Describe the 3 stages of air intake filters?

Answer 8

Stage 1 - spray eliminator, aluminium find change direction of air, catching spray and causing the majority to drop off and mainly dry air passes through
Stage 2 - knitmesh filter removes particulate matter
Stage 3 - water separation manometric leg, u bend principle. Water drains into a water trough which ensures a water seal across the bottom of filters.

Question 9

Describe the purpose of the splitter silencer?

Answer 9

The splitter silencer splits up the air flow stream which reduces air noise and buffeting.

Question 10

Describe the purpose of the stone guard?

Answer 10

Prevents large coarse particles of debris from entering the gas turbine (1 inch wire mesh)

Question 11

Describe the purpose of the transition duct?

Answer 11

Provides a smooth change from square cross section air flow to circular cords section air flow, in preparation for entering the engines air intake casing.

Question 12

Describe the cascade bend?

Answer 12

Directs the air smoothly through a 90 degree bend without causing turbulence to the already smoothed out air.

Question 13

Describe the engine intake flare?

What is it made of?

Answer 13

Seals the engine intake from the rest of the module and houses the water wash ring used for cleaning the engine.

Glass reinforced plastic.

Question 14

Describe the gas turbine module ventilation system?

Answer 14

The function of the module vent flaps is to isolate the module in the event of an emergency e.g. fire. 
When the engine is running the module vent flaps are to be open to allow airflow to cool the module and expel any exhaust fumes.

Question 15

The module is ventilated by….

Answer 15

Bernoulli’s theorem
The Venturi effect
Vent by volute

Question 16

Bernoulli’s theorem:

As a substances velocity …. The pressure ……

The ….. Pressure will draw fluid from the reservoir into the flow.

Answer 16

Increases

Decreases

Low

Question 17

Describe the process of module ventilation? Why are vent flaps fitted?

Answer 17

1. Air is drawn into the module because of the depression.
2. Air circulates around the module keeping it cool
3. A depression is formed by the rushing exhaust gases. (Bernoulli’s theorem)
4. Vent flaps are fitted to seal the module should a fire establish within.

The position of the flaps must be known at all times. When the engine is running the flaps must be open. (Flaps shut - no cooling)

Question 18

Name the 5 stages of a gas turbine cycle?

Answer 18

Induction ( intake flare )

Compression ( LP&HP compressor )

Combustion ( combustion chambers )

Power ( HP&LP and power turbines )

Exhaust

Question 19

Within the combustion chamber you have 3 types of air and 2 components. Name them.

Answer 19

Primary air
Secondary air
Tertiary air

Burner/ fuel injector
Igniter

Question 20

What percentage of primary air is there in a combustion chamber?

Answer 20

15%

Question 21

What percentage of secondary air is there in a combustion chamber?

Answer 21

10%

Question 22

What percentage of tertiary air is there in a combustion chamber?

Answer 22

75%

Question 23

What type of compressors are the LP & HP compressors?

Answer 23

Axial flow compressors

Question 24

What are the HP and LP compressors made up of?

Answer 24

Rotors and stators, air is constantly compressed as it passes through each compressor.

Question 25

What air compression ratio can be obtained?

Answer 25

19:1

Question 26

During the combustion process what is the main role of the primary air?

Answer 26

Helps to atomise the fuel and provides air for the initial combustion. ( Remember 15% )

Question 27

During the combustion process what is the main role of the secondary air?

Answer 27

To ensure complete combustion of the fuel and provides a layer of air between the fuel and the flame tube preventing flame impingement. ( Remember 10% )

Question 28

During the combustion process what is the main role of the tertiary air?

Answer 28

After cooling the combustion can the tertiary air is heated by the combustion process causing it to rise in pressure and becomes the working fluid to drive the turbines. ( Remember 75% )

Question 29

The LP and HP turbines act like water wheels, using …. Produced in combustion to drive the corresponding compressors.

Answer 29

“Working fluid”

Question 30

The HP turbine drive shaft connects back to the HP compressor and is …..

Answer 30

Hollow

Question 31

The LP turbine drive shaft passes through the HP shaft and drives the ….

Answer 31

LP compressor.

Question 32

How much energy is used by the LP and HP turbines?

Answer 32

Approximately 1/3

Question 33

The power turbine is driven in the same way as the LP and HP turbines, what does the power turbine drive?

Answer 33

A shaft into the main gearbox/generator, using the remaining 2/3 of energy from the working fluid.

Question 34

How do the remaining hot gasses exit to the atmosphere?

Answer 34

Via the exhaust funnel (remember, this funnel is what the module ventilation is connected into, allowing the air used in that process to exit aswell using Bernoulli’s theorem)