University of the Highlands and Islands
Perth College UHI
DESIGN A BELLMOUTH INTAKE FOR A GAS TURBINE
TURBO SHAFT ENGINE- ROLLS ROYCE/ALISON 250 C-10 D
Author: Rishab Anand
Academic Session 2014- 15
BEng (Hons) Aircraft Engineering Degree Course
Project Report
Acknowledgement:
I would like to express my deepest appreciation to all those who provided me
support in this project. My deepest regard is for my Project Supervisor ‘Dr Bassam
Rakhshani’, who provided me with all the resources and materials. Without his
support, motivation and encouragement, this project would have been impossible to
accomplish. He was always available to guide me in achieving all the challenges to
raise the standard of this project.
I would also like to acknowledge Dr Qusai Al-Hamdan who helped me in
understanding the engine manual to gather some of the useful parameters on which
the design is based.
Finally I would like to convey my acknowledgement for Mr Peter Peffers who along
with my project supervisor, was always available at AST Hanger in Scone to guide
me in understanding the engine, its specification and working procedures.
Contents
ABSTRACT: .................................................................................................................................... 3
1.
Introduction .............................................................................................................................. 1
1.1 Air flow ................................................................................................................................... 4
1.2 Aerodynamic Intake.............................................................................................................. 4
1.3 Aims and Objectives: ........................................................................................................... 5
2
Background ............................................................................................................................. 6
2.1 Engine: .................................................................................................................................. 6
2.2 Bellmouth intake and coefficient of discharge: .................................................................. 8
3. Bellmouth Design: .................................................................................................................... 10
3.1 Preliminary Design: ............................................................................................................ 10
3.2 Detailed Design: ................................................................................................................. 13
3.2.1 Relation between RPM of the engine, mass flow rate and pressure ratio with
Coefficient of Discharge: ...................................................................................................... 14
4. Design Analysis ........................................................................................................................ 22
4.2: Analysis Results: ............................................................................................................... 25
5
Manufacturing ........................................................................................................................ 30
5.1 Material: ............................................................................................................................... 30
5.2 Manufacturing Method: ...................................................................................................... 32
5.3 Bellmouth structure: ........................................................................................................... 33
6
Conclusion: ............................................................................................................................ 35
6.1 Further Development and Recommendation: .................................................................. 36
Bibliography................................................................................................................................... 38
List of Figures:
Figure 1 Aerodynamic duct in an airstream. (Seddon & E.L.Goldsmith, 1999) .......... 4
Figure 2 Allison 250 C-10 D placed on a test stand (eflightmanuals, 2014) ............... 6
Figure 3: The Compressor of the engine where bellmouth intake will be
assembled.
6
Figure 4: drawing of compressor Intake to show the measured radius. ..................... 7
Figure 5: mass airflow rates at different values of n1 for different temperature for air
speed 0,100,200 and 300 knots. ................................................................................ 7
Figure 6 Nomenclatures and shape of various bellmouth. (Blair & Cahoon, 2010) .... 8
Figure 7: Measurement of Discharge Coefficients (Blair & Cahoon, 2010) ................ 9
Figure 8: CD data for intake pipe bell mouths. (Blair & Cahoon, 2010) .................... 10
Figure 9 CD variations at intake bellmouths. (Blair & Cahoon, 2010)....................... 11
Figure 10: Improvement in the values of Mass flow Rate at different bellmouth
intakes. (Blair & Cahoon, 2010) ............................................................................... 12
Figure 11 Relation between Pressure Ratio and Coefficient of discharge................ 14
Figure 12: Relation between Pressure Ratio and mass flow rate of air .................... 15
Figure 13: Relation between Coefficient of Discharge and mass flow rate of air
passing through the intake. ...................................................................................... 15
Figure 14: Relation between Coefficient of discharge and RPM .............................. 16
Figure 15 Relation between mass flow rate and RPM of the engine. ....................... 16
Figure 16 Best bell design in Catia V5 with a profile of ELL: 181.39- 112.73- 242.23:
8 ............................................................................................................................... 18
Figure 17: The circular holder clamp which will attach the intake to the engine. ...... 19
Figure 18: CATIA V5 design of the bellmouth according to the requirement. ........... 20
Figure 19: Front View of the Bellmouth intake for Alison 250 C-10 D....................... 21
Figure 20: Right View of the Bellmouth intake for Alison 250 C-10 .......................... 21
Figure 21:The final mesh with a face size of half a million, used for CFD analysis. . 22
Figure 22: The figure shows different zones set for the intake and the type of ‘upper
_ wall’ as ‘wall’. ......................................................................................................... 23
Figure 23: Contours of static pressure (SI unit: Pascal) ........................................... 25
Figure 24: Graph of Pressure vs. Position along the centre line. ............................. 26
Figure 25: Contours of Static Temperature (SI Unit: Kelvin) .................................... 26
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Figure 26: Contour windows for density, which shows the maximum and minimum
value of density to be 1.225 kg/
. .......................................................................... 27
Figure 27: Static Pressure versus average Velocity graph. ...................................... 27
Figure 28: Contour of Velocity Magnitude (SI Unit: m/s) .......................................... 28
Figure 29: Vector of Velocity magnitude (SI Unit: m/s) ............................................. 28
Figure 30: Velocity Vector showing no reverse flow. ................................................ 29
Figure 31:The graph of Velocity magnitude versus Position along the centre position
axis. .......................................................................................................................... 29
Figure 32: Properties of Aluminium and Steel. (Hoglund, Soietens, Rothe, Hirsh,
Ryckeboer, & Lundberg, 2010) ................................................................................ 30
Figure 33: Stress – Strain graph for various steel and aluminium alloys. ................. 31
Figure 34: A CNC machine being operated in a workshop. (Raabi Enterprise, 2014)
................................................................................................................................. 32
Figure 35: Final design of the bellmouth (.stp file) showing thickness of the wall and
other minute specification needed for manufacturing the intake by CNC machining.
................................................................................................................................. 33
Figure 36: Bellmouth intake immediately after being delivered for assembling to the
engine. The circular holder clamp is on the right side of the bellmouth, which will be
used to attach the intake to the engine..................................................................... 34
Figure 37: Bellmouth intake after being attached to the engine using a circular holder
clamp........................................................................................................................ 34
Figure 38: A table showing all the objectives along with a summary of how each of
them was achieved................................................................................................... 36
Figure 39: Isometric view of the design. ................................................................... 39
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Abstract:
The project is to design and produce a bellmouth intake for the test run of Alison 250
C-10 D. The first phase of any design is the preliminary phase in which the data from
manufacturer and other similar type project along with their result is evaluated to
choose any particular design. Then comes the detailed design in which the design is
optimised to meet the demands and every particular bit is looked at in this phase.
Then the design is analysed very cautiously before passing it to the manufacturing
phase. The method of manufacturing and the selection of material are carefully
studied in this phase and then finally the design is manufactured.
The bellmouth intake is now, manufactured and is ready to assist the engine for the
test run. This project report deals with all the required steps which were used to
design and manufacture the intake. The performance of the design is well analysed
all the above mentioned procedures are explained in full details in this project.
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1. Introduction
1.1 Air flow
Air is a compressible fluid, but is generally considered incompressible if
travelling at low subsonic speed.
Bernoulli’s equation explains that:
= constant
The equation remains constant only for incompressible flow, where density
remains constant. “The divergence of this equation from reality is 0% at
Mach 0, 6% at Mach 0.5, 17% at Mach 0.8 and 28% at Mach 1.” (Seddon
& E.L.Goldsmith, 1999) For the proposed intake, the maximum Mach
number is around 0.2 as analyzed in Chapter 3, and hence the flow can be
considered incompressible with a constant density of 1.225
.
Air is also assumed to be an ideal gas during test run. Hence it will follow
the universal gas law:
. The ISA condition is also taken as sea
level condition.
Mass flow rate is the amount of air ingested by the intake per unit time.
=
. Mathematically it is the product of density of air, velocity of air and
the area of cross section thorough which the air is flowing and its SI unit is
kg/s.
1.2 Aerodynamic Intake
Air Intake is a part of an aircraft engine which ensures that the engine is
properly supplied with air under all conditions, and that the aptitude of
airframe is not unduly impaired in the process.
Figure 1 Aerodynamic duct in an airstream. (Seddon & E.L.Goldsmith, 1999)
Page | 4
In figure 1 when the stream flow intercepts the duct, gets divided into an
internal flow and an external flow. The internal flow feeds the engine, while
the external flow is responsible for good aerodynamics around the engine.
The internal flow velocity increases as it travels through the intake and
then through the compressor to the combustion chamber. The velocity
increases because of a gradual difference in the values of pressure at
entry (marked as position c) and exit (marked as position e) of the intake.
There are many different types of air intake depending primarily on their
purpose of application. For a moving aircraft the air enters the intake at a
particular velocity, but during test run of the engine or when the engine is
on ground, the air is stationary and a pressure difference is created in
order to make a steady flow of air into the intake. Bellmouth intake is the
most suitable intake for engine test run and is most commonly used by
Rolls Royce and other engine manufactures to test run their engines.
(A.A.Woodfield, 1968)
1.3 Aims and Objectives:
The aim of this project is to design a bellmouth intake for Allison 250 C10D engine, and to manufacture it so that the engine can perform the test
run in the test bed.
The main objectives of this project are:

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
Investigating the types of bellmouth intake design.

Reproducing the design in CATIA V5 or CAD.

Computing PR, mdot and other operating conditions.

Analysing the design in CFD.
Manufacturing the proposed design.
2 Background
2.1 Engine:
Allison 250 C-10 D currently produced as Rolls Royce 250-M is a reverse
airflow gas turbine turbo shaft engine. Its mass flow rate ranges from 0.7
to 1.3 kg/s depending of the rpm and variant of the engine. (Detroit Diesel
Allison, 1971)
Figure 2 Allison 250 C-10 D placed on a test stand
(eflightmanuals, 2014)
Figure 3: The Compressor of the engine where bellmouth intake will be
assembled.
The intake of the compressor will be the exit of the bellmouth. All the
radius and the thickness of the compressor intake were measured using a
vernier callipers and the thickness and the radius of the inner most circle
was measured to be 1.5mm and 54.865mm respectively. The radius of
Page | 6
the outer most circle was measured to be 68.5mm. All other technical
measurements are showed in the detailed CATIA V5 design in next
chapter.
R=54.865 mm
R=68.5 mm
Figure 4: drawing of compressor Intake to show the measured radius.
Figure 5: mass airflow rates at different values of n1 for different temperature
for air speed 0,100,200 and 300 knots.
Under ISA condition at sea level the temperature is15 degree Celsius
equivalent to 59 degree Fahrenheit. The outside air is static during test run,
and the air speed is assumed to be 0 knots. Keeping 59 degree Fahrenheit
Page | 7
constant, the values of n1 and mass flow rate can be obtained. This mass
flow rate can then be converted to SI unit, and the rpm can be calculated from
the %n1 value. N1 rpm maximum value is 51120. (eflightmanuals, 2014) .
These values are used in Matlab to calculate other aerodynamic values such
as PR, CD and others in the Chapter 3.2.
2.2 Bellmouth intake and coefficient of discharge:
The design of a bellmouth intake is nomenclated into three basic profiles.
They are the radius profile, airfoil profile and elliptical profile.
Figure 6 Nomenclatures and shape of various bellmouth. (Blair & Cahoon,
2010)
Selection of the best efficient profile bellmouth can be designated by
determining the coefficient of discharge in all three profiles.
Page | 8
Figure 7: Measurement of Discharge Coefficients (Blair & Cahoon, 2010)
“The effectiveness of the flow regime at any boundary at the end of a pipe
in an engine is expressed numerically as a ‘discharge coefficient’, i.e., a
Coefficient of Discharge, or CD. More briefly it is the ratio of the actual air
flowing through a cross section to the fixed geometrical area of the given
cross section. In history, and even today, they were/are measured
experimentally using a steady flow rig, much as shown in Figure 7” (Blair
& Cahoon, 2010)
By means of experiments, it is found out that CD is a factor of PR.
CD = 1.7869 – (2.9326 x PR) + (2.5275 x
(Blair & Cahoon, 2010)
Page | 9
) – (0.6446 x
)
3. Bellmouth Design:
3.1 Preliminary Design:
In an experiment conducted by Professor Gordon P. Blair (Blair &
Cahoon, 2010), in order to conclude the best bellmouth, analysed all
bellmouth profiles of same exit diameter of 23mm, but with different
lengths and corner radius. The analysis is presented in Figure 8 and it can
be observed that there is an increment of CD in all types of bellmouth, but
simple radius bellmouth has the minimum increment.
Figure 8: CD data for intake pipe bell mouths. (Blair & Cahoon, 2010)
It gets difficult to separate other types of intake, all of which shows almost
similar increment in the values of CD. The rectification of this problem can
be done by plotting and visualising another graph of the percentage
change in CD over simple radius bellmouth to the pressure ratio as in
Figure 8.
Page | 10
Figure 9 CD variations at intake bellmouths. (Blair & Cahoon, 2010)
Results from the above graph prove that the improvement in CD is directly
proportional to the entry diameter, and is pretty much unaffected from the
length of the bellmouth. It also proves that the elliptical profile has an
advantage over air foil profile in respect to values of CD. When the value
of PR lies within the range of 1.1, one can conclude that the best
bellmouth will have an advantage of 3.5% in terms of CD over simplest
bellmouth.
Page | 11
Figure 10: Improvement in the values of Mass flow Rate at different
bellmouth intakes. (Blair & Cahoon, 2010)
To illustrate the potential effect on engine performance, improvement in
air mass flow rate for all profiled bellmouth over simple radius is shown in
Figure 10. The change in the values of mass flow rate is expressed in
percentage. For pressure ratios ranging from 1.04 to 1.1, short and fat
profiled bellmouths are the best. The graph above hails elliptical profile
bellmouth, ELL-23-23-49-3 as the winner with an advantage of around
1.5%.
Page | 12
3.2 Detailed Design:
The elliptical profile bellmouth design was chosen as the final design
approach because of its advantage in the areas of coefficient of discharge
and mass flow rate, as proved above in chapter 2. The task now lies in
drafting a design compatible with the engine, which can with stand the
extremes of engine test run conditions by its physical strength and
aerodynamic performance.
Because of high market share in aerospace design, CATIA V5 was an
obvious choice as the designing tool for the bellmouth intake.
The physical specification of any intake is represented as: Bellmouth
Profile: L-De-Di-Rc. The bellmouth profile is already selected as elliptical
profile or ‘ELL’.
The bellmouth exit will be assembled to the compressor intake of the
engine. The smallest and the innermost diameter of the compressor
intake was measured as 112.73mm. This gives us the value of the exit
diameter of the bellmouth, or ‘De’ as 112.73mm. (These values are for the
external diameter, which includes the thickness of the material.)
The intake diameter of the bellmouth represented as ‘Di’ is generally
2.148 times the exit diameter. This can be proven by the fact which is
described above in Chapter 3.1, that when the pressure ratios between
intake and the exit of the bellmouth is below 1.1, the design gives the
most optimised results.
Page | 13
3.2.1 Relation between RPM of the engine, mass flow rate and
pressure ratio with Coefficient of Discharge:
The coefficient of discharge is directly proportional to the pressure ratio.
According to Bernoulli’s, pressure ratio will depend on velocity of air at the
points of entry and exit. Velocity is a parameter on which mass flow rate
depends, and mass flow rate is directly proportional to the rpm of the
engine. Therefore when the rpm increases, mass flow rate increases.
When mass flow rate increases, the velocity increases and static pressure
at exit decreases, and hence the pressure ratio increases. When the
pressure ratio increases the coefficient of discharge increases as well.
This relation is clearly described in Figure 11, Figure 12, Figure 13, Figure
14 and Figure 15.
Figure 11 Relation between Pressure Ratio and Coefficient of discharge.
Page | 14
Figure 12: Relation between Pressure Ratio and mass flow rate of air
Figure 13: Relation between Coefficient of Discharge and mass flow rate of air
passing through the intake.
Page | 15
Figure 14: Relation between Coefficient of discharge and RPM
Figure 15 Relation between mass flow rate and RPM of the engine.
Page | 16
De = 112.73 mm
Di = 112.73 x 2.148 = 242.23 mm
(An average value at a set rpm)
=
Ai = 0.046
Ae = 0.009
= 1.225 kg/
(constant as flow is incompressible)
We know that mass flow rate remains constant and at sea level Static
Pressure P0= 101325 Pa.
We can calculate the value of Ve.
Ve =
/
Ve = 90 m/s
Applying Bernoulli’s equation:
=
= constant
101325 = P2 +
P2 = 96794.95 Pa
P1 = 101325 Pa ( no dynamic pressure, hence total pressure = static
pressure.)
P1/P2 = 1.05, which lies below 1.1, and hence the aerodynamic
performance will be more optimised as concluded above from the Figures
3.1, 3.2 and 3.3.
CD = 1.7869 – (2.9326 x PR) + (2.5275 x
CD = 1.7869 – (2.9326 x 1.05) + (2.5275 x
) – (0.6446 x
)
) – (0.6446 x
)
CD = 1.7869 – 3.0792 + 2.7866 – 0.7621
CD = 0.7481. (The values calculated here is for a case when the mass
flow rate is 1.) The table below shows the PR, RPM, CD, Ve changing
with rpm.
m dot
Page | 17
n1
rpm
Ve
Pr
CD
0.5988
50
25560
48.9713
1.0147
0.7401
0.7938
60
30672
64.9241
1.0261
0.7425
0.9752
70
35784
79.7639
1.04
0.7457
1.1567
80
40896
94.6037
1.0572
0.7498
1.3608
90
46008
111.2985
1.0809
0.756
Design Specification:
L = 181.39 mm. The length was initially evaluated same as the value of
De, 112.73 mm, but the bellmouth intake will also possess various
sensors to measure pressure, temperature and other aerodynamic
parameters during test run. Hence the Length was increased, to ensure
enough space for these sensors, from 112.73 mm to 181.39 mm.
Rc = 8 mm. The radius was optimised to reduce the bending moment on
the structure as the structure will only be attached from the exit end of the
bellmouth intake. This will further reduce the weight and the surface area
of the structure, which will directly reduce the cost of the material.
This gives the profile of the proposed bellmouth design as: - ELL: 181.39112.73- 242.23: 8. All the parameters are represented in mm.
242.23
mm
Figure 16 Best bell design in Catia V5 with a profile of ELL: 181.39- 112.73242.23: 8
Page | 18
A circular holder clamp as shown in Figure 17 was the most basic way to fix the
bellmouth structure to the engine.
Figure 17: The circular holder clamp which will attach the intake to the engine.
The compressor outer circle and the bellmouth inner circle (Figure 18) will
be attached together by the circular holder clamp. This arise the need of an
inner circular structure in the bellmouth, which will be more than the outer
circle of the bellmouth.
The structure will also contain various sensors to measure aerodynamic
parameters. Hence a bulge needs to be designed on the intake which can
contain these sensors without compromising the strength and performance
of the bellmouth intake.
The thickness of the structure is also variable at different positions to reduce
weight where ever possible without affecting the strength in any means. The
thickness lies in a range of 1.5 mm at the exit end to 8mm and to 13.635 mm
Page | 19
at the bulge and at the circle which goes inside the circular holder clamp.
Space for
instruments
Inner or big
radius circle
that will be
fixed into the
clamp holder.
Outer or
smaller
radius circle
that will be
placed
inside the
compressor
intake
Figure 18: CATIA V5 design of the bellmouth according to the requirement.
The figure clearly shows the smaller circle, the larger circle and the bulge which can
be used as space to assemble the sensors.
The drafted design for the intake is shown below in the Figure 19 and Figure 20.
Figure 19 shows the front view of the bellmouth, while Figure 20 shows the right view
of the bellmouth intake. The figure shows all the physical specification of the
bellmouth design. The back view will be same as that of the front view, and the left
view will not be able to show the smaller circle radius as they will be hidden behind
the bigger circle. The isometric view of the intake is shown in the Appendix.
Page | 20
Figure 19: Front View of the Bellmouth intake for Alison 250 C-10 D
Figure 20: Right View of the Bellmouth intake for Alison 250 C-10
Page | 21
4. Design Analysis:
4.1 Meshing and Boundary Conditions:
A 2D bellmouth of the same profile was designed in CATIA V5 and then
imported to Gambit in order to do the meshing. All the nodes and the faces
were meshed, and the number of faces was set to half a million. The higher
number of faces is accountable for the accuracy of the result. Increasing the
number of nodes will increase the number of faces, but after a maximum
limit, the size of the mesh will not be able to contain within the memory of
normal computers, and a computer with much higher memory space and
speed will be required to compute the mesh. Henceforth the mesh of the
intake was set to half million.
Figure 21: The final mesh with a face size of half a million, used for CFD
analysis.
This mesh file is then exported as .msh file, so that the mesh can be read as
a case file in the Fluent. The case file is then scaled and different zones are
set along with the type. The operating values of each zone are set
respectively in order to define the boundary conditions as shown in Figure
Page | 22
22.
Figure 22: The figure shows different zones set for the intake and the type of
‘upper _ wall’ as ‘wall’.
For the bellmouth intake, six different zones are set which are as follows:
ID 1. Default-interior: It is set as Type interior and it represents all the
available space within the boundaries of the intake walls.
ID 2. Inlet _ air: It is set as Type fluid, as the space available within the
bellmouth walls will be available for air to flow through it, and air can be
defined as a type of fluid.
ID 3. Inlet _ flow: It is set as Type ‘pressure inlet’, and the operating pressure
is set to 101325 Pa. The test run will be conducted on the ground at sea
level, and according to ISA conditions pressure at sea level is 101325 Pa.
The Temperature is set to 288.15 K, and the turbulence specification method
is set to K and Epsilon. All other values are set to 1.
ID 4: Lower _ wall: It is set as Type ‘wall’, where the wall is set as stationary
and shear condition is set to no slip. All other values from heat flux to
roughness height are set to 0.
ID 5: outlet: This zone is set as Type ‘pressure outlet’. The pressure ratio
can lie within the range of 1.04 to 1.1 for optimised results, and the Pressure
at exit was calculated above using Bernoulli’s Equation and was found out to
be 96794.95 Pa, with a pressure ratio of 1.05.
Page | 23
ID 6: Upper _ wall: It is set as Type ‘wall’, where the wall is set as stationary
and shear condition is set to no slip. All other values from heat flux to
roughness height are set to 0, same as the lower wall.
After defining the boundary condition, the next step is ‘Solution Initialization’.
In this step, the ‘Compute From’ section is set to inlet _ flow and the
‘Reference Frame’ is set to ‘Relative to Cell Zone’. The Initialization Values
are set automatically. These values are the applied and the Init command is
executed. Then the iteration window is selected, in which the Iteration rate
can be set depending on the capabilities of the computer. It takes about 2
second for each iteration. So, an iteration of 100000 can take up to 200000
seconds, which means up to 3 days nonstop. For the analysis shown below
the iteration was selected as 1000, which took around half an hour to
complete. The iteration rate can always be increased along with the mesh
size for more detailed result.
Page | 24
4.2: Analysis Results:
Pressure Contour:
The pressure contour lines are also called an isobar. It is a line of constant
pressure, can be a region of constant pressure as well if the contour option
is filled, as shown in Figure 23. The pressure contour is inversely
proportional to that of velocity.
Figure 23: Contours of static pressure (SI unit: Pascal)
The graph bellow in Figure 24 also shows that the pressure is gradually
decreasing as the flow is moving along the axis, from entry to the exit position.
The pressure is maximum at position 0, or entry position with a value of 101325
Pa, and the minimum value of pressure is at exit or at position 0.18 m, with a
value of 96794.95 Pa.
Page | 25
Figure 24: Graph of Pressure vs. Position along the centre line.
Temperature Contour:
The temperature contour lines are also called an isotherm. It is a line that
connects points of constant temperature. It can be a region of constant
pressure, filled with a common colour, as well if the contour option is filled,
as shown in Figure 25.
Figure 25: Contours of Static Temperature (SI Unit: Kelvin)
It can be observed that there is almost no major change in the values of
temperature, but the slight change in the temperature cannot be seen in the
values presented by it. The colour change might be because of very minute
error in the operating condition or boundary condition.
Page | 26
Density:
The velocity of air flowing through the bellmouth intake never approaches any
value close to Mach 0.4 or around 136 m/s. So the flow is believed to be
incompressible, as proved above in Chapter 1.
Hence the density will remain constant throughout the bellmouth intake.
Minimum Density
Maximum Density
Z
Figure 26: Contour windows for density, which shows the maximum and
minimum value of density to be 1.225 kg/
.
Velocity Contour:
Velocity is the most prime factor which justifies the design parameters of the
bellmouth intake. According to Bernoulli’s the total pressure at any point
inside the intake remains the same, but the above pressure contour shows
that the static pressure gradually decreases. This means that the dynamic
pressure gradually increases which will increase the velocity vector as the
flow travels along the intake as shown in Figure 27.
Figure 27: Static Pressure versus average Velocity graph.
Page | 27
It can be clearly observed from the above Figure 27 that as the static pressure
decreases, velocity increases.
Figure 28: Contour of Velocity Magnitude (SI Unit: m/s)
The above Figure 28 shows the contour of velocity magnitude. All the regions
of same velocity are filled with a common colour. The maximum velocity
remains 85.6 m/s represented by red colour, and the minimum velocity remains
0, at the entry tip point, middle of Rc. The flow is stagnated at that point.
The most successful fact of this analysis which justifies the design of the intake
meets the requirement is that there is almost no reverse flow, as seen in Figure
29 and Figure 30. There can be a possibility that the reverse flow cannot be
observed at this iteration rate and scale, but even if that is the case, the reverse
flow vectors will be so less, that they can be neglected.
Figure 29: Vector of Velocity magnitude (SI Unit: m/s)
Page | 28
Figure 30: Velocity Vector showing no reverse flow.
Figure 31: The graph of Velocity magnitude versus Position along the centre
position axis.
The graph above shows the average velocity at different positions. The maximum
velocity was 85.7 m/s as observed from the contour, but the maximum average
velocity is just below 68m/s at the exit position. It also shows that even at the
entry position, the average velocity was 48 m/s.
Page | 29
5 Manufacturing
5.1 Material:
An intake can be build using various different materials ranging from steel
to aluminium alloys.
There are many differences in physical properties as well as mechanical
properties of both the material. The low density of aluminium leads to low
weight, and high strength to weight ratio of the material. This is one of the
driving reasons behind the use of aluminium in many structural
applications in the development of the aircraft industry. Although the low
density is a favouring property, in some cases it can be a bit
disadvantageous. When dynamic behaviour of the structure is considered,
aluminium structure is prone to more vibration because of its low density.
Properties
SI Unit
Aluminium
Steel
Density,
Kg/
2,700
7,800
Young Modulus, E
N/
70,000
210,000
Shear Modulus, G
N/
27,000
81,000
Poisson Ratio, v
0.33
0.3
Coefficient of linear thermal
23 x
12 x
expansion
Figure 32: Properties of Aluminium and Steel. (Hoglund, Soietens, Rothe,
Hirsh, Ryckeboer, & Lundberg, 2010)
The Young Modulus plays an important role in determining the structural
behaviour of a material. In the case of Aluminium and Steel, the young
modulus of aluminium is 1/3rd of steel, and this is a disadvantage of
Aluminium compared to steel. The low value of young modulus has a big
influence on the deformation of a structure. It is also responsible for higher
sensitivity to stability problem, as it leads to bulking of structures. To solve this
problem of strength and deformation, aluminium alloys started being used in
the aircraft industry.
The mechanical properties of aluminium alloys vary from low strength (pure
aluminium 1050A), medium strength 5xxx and 6xxx series alloys (comparable
Page | 30
to mild steel S235), to high strength 7xxx alloys (comparable to high strength
steel S355). (Hoglund, Soietens, Rothe, Hirsh, Ryckeboer, & Lundberg,
2010)
The aluminium alloys cannot match the strength of titanium alloys and high
strength steels, but strength is not the governing factor in the design of many
structures. Aluminium 5xxx series and 6xxx series are the most commonly
used aluminium alloys used in aircraft building and civil engineering structural
application.
Figure 33: Stress – Strain graph for various steel and aluminium alloys.
The stress – strain values described above are applicable for a temperature
within the range of −30 to 80 °C. If the temperatures are above 80 °C, the
strength for aluminium decreases faster than that of steel. Hence for
Aluminium the strain to failure highly increases as compared to steel. At
temperatures below −30 °C, the stress-strain behaviour for aluminium
remains more or less constant, while certain structural steels become brittle at
low temperatures. But for test run the temperatures are not going anywhere
close to the extremes. (European Alluminium Association, 2000)
Cost is another important factor when it comes to selection of the material.
Composites materials could be a major point of discussion for the selection of
material, but because of high cost and low fracture point, the main competition
was considered between steel and aluminium alloys.
Because of high application, proven features and know how in aircraft and
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civil industry, easy availability, low cost, high strength to weight ratio,
considerable young modulus, and moderate strength (comparable to mild steel
S235), Aluminium Al 6xxx alloy was chosen over other Aluminium alloys and
steel for the manufacturing of bellmouth intake.
5.2 Manufacturing Method:
Computer Numerical Control Machine or CNC machine is a new innovative
technology which uses software to manufacture designs quite easily, which
could be far too complicated to manufacture using manual machines even by
skilled workers.
Figure 34: A CNC machine being operated in a workshop.
(Raabi Enterprise, 2014)
CNC machines have a lot of advantages as it produced quality product. The
machine is operated using software, and hence it produces exact replica of
the design. The accuracy level is almost up to 0.001mm.
In CNC machining, the tools operated by the machine functions through a
numerical control. (Lowrance, 2013). A CNC machining language called G –
code, controls all the features like coordination, speed, feed rate and location
to customise the object that is being produced. The computer can even
control the velocity and position of the machine very precisely to produce best
quality product.
For producing a bellmouth from CNC machine, first a CAD drawing is created
or CATIA V5 file is converted to .stp file as shown in the Figure 5.4, then a G
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– code is created, as the CNC machine can only understand G – code
language. (Thomasnet, 2015)
Figure 35: Final design of the bellmouth (.stp file) showing thickness of the
wall and other minute specification needed for manufacturing the intake by
CNC machining.
The program is then loaded, and a test of the program is conducted by an
operator to ensure that there is no fault in the program. This trial run is
more popularly known as ‘cutting air’, and is a very prime step to ensure
the safety of the machine and the material, as any wrong tool position or
speed can result in the production of scrap material and a damaged tool.
5.3 Bellmouth structure:
After manufacturing, the bellmouth intake was very high on quality with
very smooth surface, and pin point accuracy in its statistics.
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Bellmouth intake
Circular Holder
Figure 36: Bellmouth intake immediately after being delivered for
assembling to the engine. The circular holder clamp is on the right side of
the bellmouth, which will be used to attach the intake to the engine.
Engine compressor
Circular holder
Bellmouth intake
Engine exhaust
Figure 37: Bellmouth intake after being attached to the engine using a
circular holder clamp.
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6 Conclusion:
The project to design and manufacture a bellmouth intake, for the test run of
Alison 250 C-10 D engine, has created pathways for learning new mechanical
designing skills such as 3 – D bellmouth design in CATIA V5, and working
with simulation software such as Computational Fluid Dynamics, CFD
(FLUENT). It has also provided extensive learning in the fields of
aerodynamics and project management.
Product / Objective
Summary Review
Investigating the types of
A study of simple radius, air foil profile and elliptical
bellmouth intake design.
profile of bellmouth. Concludes that elliptical ones are
the most efficient ones.
Calculating PR, mdot, CD and
Engine manual was used to gather some useful
other operating conditions.
statistics. Other parameters were calculated
numerically, using various theorems and equations.
Reproducing the design in
CATIA V5 was opted as a designing tool to produce
CATIA V5 or CAD
the design, based on the engine specification and
calculated results.
Analysing the design in CFD
Gambit was used to create the mesh, and then the
structure was analysed in Fluent. The results were
quiet good, and approved by the supervisor.
Manufacturing the proposed
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A CNC machine operating company was approached
design
by the help of project supervisor, and then the design
was finally manufactured.
Figure 38: A table showing all the objectives along with a summary of how
each of them was achieved.
All the objectives were achieved successfully, on time as per the proposed
Gantt chart. The Table above Figure 38 shows a brief summary of how all the
projects were achieved. The success of the project can be justified by the
results obtained in CFD (FLUENT). If we observe the mass flow rate carefully,
it comes to be slightly less than 1. The maximum velocity is over 85 m/s, but
the average velocity at exit is 67 m/s. This gives a mass flow rate of 0.7 kg/s,
which is less than the required 1 kg/s. This difference is mainly because the
CFD analysis was done in a 2-D design. In 3-D circumstances, this error
could have easily been overcome. The pressure ratio, PR of 1.05 is just what
was expected, and the coefficient of discharge, CD was found to be 0.7481.
The complete cost of the project was significantly reduced, as the necessary
software was shared instead of being purchased. The CNC machining, and
the material (Aluminium 6x) was a bit expensive, but significantly cheaper
than other competitive like composites. The total cost of the project was that
quoted by the CNC machining company, which was 1300 pounds.
The end product, which was the bellmouth, was ready to be delivered to the
customer (College) for the test run of the engine, but a sudden shift of the
engine from its earlier location in the Scone Airport, Hanger 4 to the Brick
works in Perth Campus delayed the test run of the engine
6.1 Further Development and Recommendation:
The bellmouth intake is now attached to the engine. The design features
include space where the instrumentation systems can be attached. The
instruments can be pressure, temperature and other quantities measuring
gauges. The result provided by them can then be compared to the fluent
analysis to measure any changes in the quantities, if any.
The Computational Fluid Dynamics (FLUENT) was done on the 2D section of
the bellmouth. A 3D analysis can be done on the design and the obtained
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results can be compared with the 2D result and the result that will be obtained
from the engine test run. Although the numerical value of temperature never
changes, but the isotherm or the temperature contour shows some difference
in colour. This can be some very low changes in temperature, but the limit in
the number of significant digits might be the reason for the change not to be
traced (even though it is very low). The reason can be worked for so that a
constant contour can be generated. The mesh generated for analysis in only
half a million. More dense mesh can be generated along with high iteration
rate, to get more accurate result. This result can then be compared for
reverse flow in velocity contour and Temperature contour.
Page | 37
Bibliography
A.A.Woodfield. (1968). AERONAUTICAL RESEARCH COUNCILREPORTS
AND MEMORANDA. London: LONDON: HER MAJESTY'S STATIONERY
OFFICE .
Blair, G. P., & Cahoon, W. M. (2010, September 1). Best Bell. SPECIAL
INVESTIGATION : DESIGN OF AN INTAKE BELLMOUTH , 34-41.
Detroit Diesel Allison. (1971, September 15). Allison Gas Turbines. Operation
and Maintenance Manual . Indiana, USA: Detroit Diesel Allison.
eflightmanuals. (2014). Alison 250 C10-D. eflightmanuals . USA: efm llc.
European Alluminium Association. (2000). Properties of Al. Europe.
Hoglund, T., Soietens, F., Rothe, J., Hirsh, J., Ryckeboer, M., & Lundberg, S.
(2010). aluMATTER. aluMATTER . UK: University of Liverpool.
Lowrance, C. (2013, December 2). CNC Machines. Lawrance Machine .
Houston, Texas, USA.
Raabi Enterprise. (2014). operation . operation and maintenance .
Seddon, J., & E.L.Goldsmith. (1999). Intake Aerodynamics. Oxford: American
Institute of Aeronautics and Astronautics, Inc.; Blackwell Science Ltd. .
Thomasnet. (2015). CNC Machining. More about CNC machining . Thomas
Publishing Company.
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Appendix:
Appendix 1:
Figure 39: Isometric view of the design.
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Appendix 2:
Matlab Program
P1=101325;
De = 112.73/1000;
maxn1=51120% maximum n1 from the engine manual
Di = 112.73 * 2.148/1000;
md=[1.32,1.75,2.15,2.55,3]% mass flow rate of air from the manual
mdot=md.*0.4536
n1=[50:10:90]
rpm=n1.*maxn1/100
Ai = pi*((Di/2)^2);
Ae = pi*((De/2)^2);
rho = 1.225;
%We know that mass flow rate remains constant and at sea level Static
Pressure P0= 101325 Pa.
%We can calculate the value of Ve.
Ve =mdot./(rho*Ae);
%Applying Bernoulli’s equation:
P2=P1-(0.5*rho*Ve.^2);
PR=P1./P2;
CD = 1.7869 - (PR.*2.9326) + (PR.^2.*2.5275)- (PR.^3.*0.6446);
plot(PR,CD)
ylabel('Coefficient of Discharge')
xlabel('Pressure Ratio')
title('CD vs PR')
plot(rpm,CD)
ylabel('Coefficient of Discharge')
xlabel('rpm')
title('CD vs rpm')
plot(PR,mdot)
ylabel('mass flow rate')
xlabel('Pressure Ratio')
title('mdot vs PR')
Page | 40
plot(mdot,CD)
xlabel('mass flow rate')
ylabel('Coefficient of Discharge')
title('mdot vs CD')
plot(mdot,rpm)
ylabel('RPM')
xlabel('mdot')
title('RPM vs ma')
The result of this Matlab Program gives different values at different mass flow
rate.
mdot =
0.5988
0.7938
0.9752
70
90
1.1567
1.3608
n1 =
50
60
80
rpm =
25560
30672
35784
40896
46008
Ve =
48.9713 64.9241 79.7639 94.6037 111.2985
P2 =
1.0e+004 *
9.9856
9.8743
9.7428
9.5843
9.3738
1.0261
1.0400
1.0572
1.0809
PR =
1.0147
CD =
0.7401
Page | 41
0.7425
0.7457
0.7498
0.7560