Gas Turbines Flashcards
What are the Advantages of gas turbines?
- Allow the ship to get underway quickly.
- Ease of operations and emphasis on remote control.
- high power to weight ratio.
- minimum ship-borne maintenance.
- Lower man-power requirement
Air intake filters
Describe the stages:
In 3 stages
Stage 1: Spray eliminator
Stage 2: Knitmesh filter
Stage 3: Water separation via Spray eliminator.
Air leaving the filter unit is now guaranteed to be “water and dirt free”.
Splitter & silencer.
What does each of these do?
The splitter silencer splits up the air flow stream which reduces air noise and buffeting.
Air passes over aerofoil shaped vanes which “straightens” air flow and reduces resistance to air flow.
Stone guard
What is the purpose of a stone guard?
Prevents large/coarse particles (bits and beaks) of debris from entering the gas turbine (1 inch wire mesh to prevent damage)
Imbalance causes vibration- brick in washing machine.
Transition duct. What’s the purpose of this part?
This provides a smooth change from square cross section air flow to circular cross section air flow, in preparation for entering the engines air intake casing.
What is cascade Bend?
Directs the air smoothly through a 90 degree bend without causing any turbulence to the already smoothed out air flow.
If any turbulence of the air entering the engine will affect the engines performances.
Engine flare intake
Glass Reinforced Plastic
Seals the engine intake from the rest of the of the module and houses the “water wash ring” (windscreen washer jet) used for cleaning the engine.
Module ventilation
The function of the module vent flaps are always open.
- Air is drawn into the module because of the depression formed at the other end.
- Air circulates around the module keeping it cool.
- A depression of air is formed by the rushing exhaust gasses (refer to Bernoulli’s theorem)
- 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).
How does module ventilation work?
The module is ventilated by: Beenoulli’s theorem. The Venturi effect Vent by volute ( V x V) The low pressure (depression) will draw fluid from the reservoir into the flow.
Gas turbine cycle
A gas turbine ha five stages to its cycle: • Induction • Compression • Combustion • Power • Exhaust
Gas turbine construction
Intake flare LP compressor HP compressor Combustion chambers HP turbine LP turbine Power turbine
Construction of a
Combustion chamber
Burner/ fuel injector Primary air (15%) Secondary Air (10%) Tertiary Air (75%)
Combustion processes:
(1)Combustion process
Primary air.
Primary air (15%) helps to atomise the fuel and provides air for the initial combustion.
Combustion process
(2) Secondary air
Secondary air
10% is used to ensure complete combustion of the fuel and provides a layer of air between the fuel and the flame tube preventing flame impingement.
Combustion process:
(3) Tertiary air
Tertiary air 75%
After cooling the combustion can the tertiary air is heated by the combustion process causing it rise in pressure and becomes the “working fluid” to drive the turbines
Power turbine
The power turbine is driven in the same way the LP & HP turbines and drives a shaft into the main gearbox/ generator. The remaining 2/3 of energy from the working fluid is used up by the power turbine.
Exhaust
The remaining hot exhaust gasses exit to atmosphere via the funnel.
Definitions:
Working fluid
Working fluid- any gas or liquid that can do work by expansion or flow, or can be compressed or made to flow
Definitions:
Turbine
Turbine
A bladed spool designed to rotate when acted on by a working fluid.
Definitions:
Compressor
Compressor
A bladed spool designed to do work on a fluid when it is rotated.
Propulsion configurations
IEP- Integrated Electric Propulsion (type 45)
CODLAG- Combination Of Diesel eLectric and Gas
COGAG- Combination Of Gas And Gas
COGOG- Combination Of Gas Or Gas (big and small Gas Turbines)
Function of a gas turbine (purpose)
Gas turbines convert heat energy into rotary motion for ships propulsion
Gas turbine definition
Converts heat energy into rotary motion for ship propulsion
Gas turbines types
Spey, WR21
