ENGINEERING TRIPOS PART IB – 2011/2012
PAPER 8 - SELECTED TOPICS (1)
Aerothermal Engineering
Design of a Jet Engine
Leader:Dr C.A. Hall
Timing: Weeks 1-4 Easter term
Structure: 14 lectures + 2 examples classes, 4 lectures/week
AIMS
The aims of the course are to enable students to:
- Understand why current
engines on large airliners look as they do, how they work and how they are
specified.
- Determine what is needed to propel a new large airliner.
- Appreciate the mixture of
physical modelling and empirical input necessary to make the decisions to
allow a design to proceed, as well as the need for compromises.
OBJECTIVES
During the course students should be able to:
- Calculate the major
parameters of the engine (this will be carried out in the form of exercise
questions throughout the course).
- Select a design choice of engine.
- Sketch a cross-section of
the engine showing principal components with appropriate parameters.
- Calculate the effect of
speed and altitude on engine performance.
SYLLABUS
Modern jet engines are amongst the most expensive mechanical engineering devices
to design and develop; a new engine is expected to cost around one billion
pounds. Why is it so expensive? Why do they look the way they do?
Many of the most important decisions are taken at an early stage of design
using fairly simple procedures, similar to those that can be used in lectures
and example classes. The constraints, especially those associated with material
properties, need to be known or specified, together with estimates for the
likely level of aerodynamic performance. From these the desirable type of
engine configuration can be specified, preliminary choices for the main
components (compressor and turbine) can be made and a sketch of the engine
layout can be drawn.
1. Introduction to Aircraft Propulsion
- Operating principles,key aircraft parameters, nacelle/wing arrangments.
- Aircraft aerodynamics, sizing the wing, lift-drag-range relationships.
- Breguet range equation, estimation of aircraft fuel burn and emissions.
2. Generation of Thrust
- Momentum analysis,
propulsive efficiency.
- Choice of engine type for
given duty; high subsonic cruise compared with supersonic operation.
3. Thermodynamic Analysis of Gas Turbine
- Power generation: effect
of pressure ratio, temperature ratio and component efficiency.
- Jet propulsion as a means
for utilisation of power.
4. High Speed Flow of Gas
- Subsonic and supersonic
flow, nozzle flow, choking.
5. Choice of Engine
- Selection of bypass ratio
and calculation of corresponding engine mass flow.
- Determination of fuel
consumption.
- Selection of fan diameter for performance, noise and weight brade-offs.
6. Dimensional Analysis
- Dynamic scaling of jet engine.
- Start-of cruise is the design condition - estimating thrust and fuel consumption at off-design conditions, such as take off.
- To consider requirements for thrust in case of engine failure at take off or cruise.
7. Turbomachinery Principles
- General introduction to
operation of compressors and turbines.
- Selection of number of
stages in compressor and turbine.
8. Appraisal of Design
- Having specified overall
size, bypass ratio, turbine inlet temperature, sketch engine layout and
compare with existing designs.
