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MECH0024
Professor Ian Eames
Coursework Assignment 3
2020-2021

State any assumptions that you use in your analysis and references to any material
you use. Submission is either via Word document or pdf only.
Make use of a compressible flow calculator (eg
http://www.dept.aoe.vt.edu/~devenpor/aoe3114/calc.html).

1. A tank of compressed air with initial pressure 0 = 500 kPa at ambient temperature
0 = 293K is opened rapidly. The outlet is modelled as a converging-diverging
nozzle:

The tank and nozzle are characterised by cross-sectional areas 1, 2, 3 and 4 at
the points 1, 2, 3 and 4 along the tank. The area ratios are related by
1
2
= 1,
2
3
=
100 and
4
3
= 2.0.

The back pressure is = 100 kPa.

The mass flow rate of air escaping the nozzle is 1 kg s−1:

a) Sketch the variation of the Mach number along the axis of the tank (from inside) to
the nozzle exit.
[35 marks]
b) Estimate the thrust force exerted by the exit flow.

[15 marks]

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2. Supersonic inlet buzz is a serious problem for supersonic jet engines. Describe
a) how is buzz generated,
[25 marks]
b) how is buzz reduced.
[25 marks]
Illustrate your discussion with typical numerical values and suitable references. The
word limit for the whole of question 2 is 300 words. 