iii
ANALYSIS ON THE FLOW AND PRESSURE DISTRIBUTION FOR ACTUAL
STENOSIS IN TRACHEA
ZULIAZURA BINTI MOHD SALLEH.
A project report submitted in partial fulfilment of the
requirements for the award of the degree of
Master of Engineering (Mechanical)
Faculty of Mechanical Engineering
Universiti Teknologi Malaysia
DECEMBER 2010
iii
Sincerely dedicated to Abah, Mama, my fiancée, family members and friends;
My all times beloved.
iv
ACKNOWLEDGEMENT
Thanks to Almighty Allah SWT, the most gracious the most merciful, who gave
me the knowledge, courage and patience to accomplish this thesis. May the peace and
blessings of Allah be upon Prophet Muhammad SAW.
To my parents and my family, I love to take this opportunity to say thank you for
your entire support trough out this time. Without all of your support, I’m nobody in this
world. To the organization that sponsor my scholarship and also my supervisor, Assoc.
Prof.Dr. Kahar Osman, here I express my gratitude for all valuable helps, suggestions,
advices and continual supervision for the whole period in completing this study.
Not to forget my dearest fiancée, who always bear with me and encourage me in
finishing my study and guiding my life. A special of appreciation to all my friends and
CFM Lab’s members on their willingness to help and teach me when I’m facing trouble
along this time. It means a lot to me and I will not forget all your kindness. A credit for
my roommate on her thoughtful and consideration on me all this long. Thanks a lot.
Finally, for all that involved direct or indirect in my life, thanks for the support
that help me to facing any difficulties bravely.
v
ABTRACT
Knowledge of flow inside the human airway is very important for medical practitioner to
make accurate diagnosis. With the presence stenosis inside the airway, the flow will be
changed significantly and will directly affect the input to the main bronchi. In this study,
patient-specific image is used and remodelled using computational fluid dynamic
software to simulate the flow within the trachea. The image contains one stenosis which
was then reconstructed to other locations. This procedure will enable the study of flow
behaviour in the trachea with different stenosis locations. Emphasis of analysis is
focused on the flow and pressure distribution along the main airway. For each model,
computations were carried out in three different flow rates which are 15 l/min, 60 l/min
and 100 l/min corresponding to regular human activity which are resting, normal and
heavy excersice breathing, respectively. The results show as stenosis located at the upper
third of the trachea, the pressure drop along the trachea are insignificant in every
breathing condition but differ to the velocity where the maximum velocity is increase as
the flow rate increase. For stenosis located at the lower third or the trachea, both pressure
drop and velocity did effect clearly as the flow rate increase. The effect of different
location of the stenosis on the velocity distribution along the centerline shows similar
increment in every flow rate and the risk in breathing difficulties if the patient having a
stenosis at the third location is three times higher compare to the first location if the
patient in resting condition. It increases to five times higher when doing the regular
activity and eight times higher if the patient doing heavy exercise. The comparison is
based on the same size of the stenosis.
vi
ABSTRAK
Pengetahuan berkaitan dengan aliran udara di dalam ruang penafasan manusia
adalah amat penting bagi kumpulan perubatan dalam membuat rawatan dan keputusan
yang tepat. Stenosis dalam trakea memberi kesan besar terhadap pembahagian input ke
bahagian utama bronkus. Dalam kajian ini, imej geometri yang spesifik dari pesakit yang
mengalami stenosis digunakan untuk dijadikan model dan dengan menggunakan perisian
perkomputeran bendalir dinamik,simulasi aliran udara sepanjang trakea dijalankan. Imej
stenosis tersebut kemudiannya di struktur semula ke lokasi-lokasi yang berbeza untuk
mengkaji kesan kedudukan lokasi stenosis terhadap sifat-sifat aliran di dalam trakea.
Kajian ini tertumpu kepada taburan aliran dan juga tekanan sepanjang ruang utama
pernafasan manusia. Simulasi di jalankan dengan menggunakan tiga kadar aliran yang
berbeza iaitu 15 l/min, 60 l/min dan juga 100 l/min. yang mewakili aktiviti harian
manusia: keadaan rehat, normal dan juga ketika melakukan senaman berat. Hasil
daripada kajian menunjukkan sekiranya stenosis berada di bahagian atas trakea,
perubahan tekanan sepanjang trakea mengalami perubahan yang kecil bagi setiap
kondisi pernafasan tetapi kelajuan maksimum aliran meningkat sekiranya kadar aliran
input meningkat. Bagi stenosis di bahagian bawah trakea, peningkatan kadar aliran
menunjukkan efek yang ketara ke atas perubahan tekanan dan juga halaju aliran. tetapi
bagi taburan halaju sepanjang trachea, ianya memberikan paten yang hampir sama bagi
setiap kedudukan stenosis. Akhir sekali, risiko dalam pengalami kesukaran bernafas
adalah tiga kali lebih tinggi bagi pesakit yang mengalami stenosis di bahagian bawah
berbanding atas jika pesakit dalam keadaan rehat, lima kali lebih berisiko dalam keadaan
normal dan lapan kali lebih berisiko sekiranya melakukan senaman berat.
vii
TABLE OF CONTENT
CHAPTER
1
TITLE
PAGE
DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGEMENT
iv
ABSTRACT
v
ABSTRAK
vi
TABLE OF CONTENTS
vii
LIST OF TABLES
x
LIST OF FIGURES
xi
LIST OF SYMBOLS
xiii
INTRODUCTION
1.0
Overview
1
1.2
Objectives
2
1.3
Scope
3
viii
2
3
4
LITERATURE REVIEW
2.1
Overview of human respiratory system
4
2.2
Trachea
5
2.3
Trachea stenosis
7
2.4
Trachea stenosis effect to velocity and pressure distribution . 9
2.5
Effect of the stenosis location to the flow characteristic
9
2.6
Actual modeling
10
2.7
Current study
12
METHODOLOGY
3.1
Introduction
13
3.2
Simulation model
14
3.3
Boundary Condition
17
3.4
Governing Equations
19
3.5
K-ε turbulent model
20
3.6
Summary of the methodology throughout the process
21
RESULT AND DISCUSSION
4.1
Overview
22
4.2
Velocity distribution
23
4.3
Pressure Distribution
26
4.3.1
Risk due to location of stenosis.
29
ix
5
CONCLUSION
33
REFERENCES
36
APPENDIX A
38
APPENDIX B
39
APPENDIX C
43
x
LIST OF TABLE
TABLE NO
3.1
TITLE
Parameters at all trachea model for three
different breathing conditions
PAGE
18
xi
LIST OF FIGURES
FIGURE NO
TITLE
PAGE
2.1
Respiratory system
5
2.2
Trachea and major bronchi of the lungs
6
2.3
Normal bifurcation (Zuhairi, 2009)
7
2.4
Obstructive airway (Zuhairi, 2009)
8
2.5
Tracheal stenosis
8
2.6
Suggested location for tracheal stenosis
10
(Freitag et al.(2007), A proposed classification system
of central airway stenosis, European Respiratory Journal)
2.7
Example of trachea model without stenosis.
11
(a) actual model (b)simplified model
3.1
Four separate model of trachea and main bronchi
15
xii
3.2
3D model of the whole respiration system reconstructed
16
from CT-scan images
3.3
(a) Actual trachea model extract from the whole respiration
17
system (b) Actual trachea model ready to be simulated
4.1
Central velocity distribution of each model in Q=15 l/min
23
4.2
Central velocity distribution of each model in Q=60 l/min
24
4.3
Central velocity distribution of each model in Q=100 l/min
24
4.4
Central pressure distribution of each model in Q=15 l/min
26
4.5
Central pressure distribution of each model in Q=60 l/min
27
4.6
Central pressure distribution of each model in Q=100 l/min
28
4.7
Range of P/Po between inlet and bifurcation area for each
30
location of stenosis and flow rates
4.8
Risk of stenosis for every location and flow rate
31
xiii
LIST OF SYMBOLS
SYMBOLS
A
area
C
velocity of sound
E
total energy
g
local acceleration of gravity
L
length
Re
Reynolds number
Q
volume flow rate
U
mean velocity
D
diameter
ρ
density
xiv
v
kinematic viscosity
P
pressure
P0
stagnation pressure
μ
viscosity
V
velocity
V0
stagnation velocity
l
liter
min
minute
1
CHAPTER 1
INTRODUCTION
1.0
Overview
The flow in the bifurcating lung airway is one of the most basic and revealing
problems in the general case of the breathing physiology. It influence drug particle
delivery patterns, pollution dispersion and so on that related to respiration system. These
days, the flow inside the human airways is gaining attraction to the researchers to choose
as a subject of study either doing by experimental or numerical method. In fact, human
airways flow studies have been carried out by many researchers previously to provide
the solution especially for breathing problems.
Due to the advanced development in the computational capability and
computerized tomography (CT-scan), it offers an alternative to study a physically
realistic model for the human airways. Basically, human anatomy and the respiration
process are converted into simulation to understand its behaviour in the airway flow.
However, knowledge of the airflow mechanism within the airways is the first thing that
2
needs to take into account before proceed the study. This is where the CFD tools were
come as the handy tools where the characteristic and the condition that happen inside the
human airways can be simulate and presented.
The airways networks has quite small dimension and it is difficult to retain
dynamic similarity to the physical model. Therefore, most of the studies were limited up
to third generations. But the most crucial part that needs to be considered is the main
trachea where it plays as a main vessel for the air to reach the lung in respiration process.
If happen any obstruction in this area, it can lead to problems in breathing compared to if
the obstruction happens in one of the airways networks (right or left side) since human
still can survive if one side of the network is blocked.
In this study, the actual model of the trachea diseases patients will be used to
obtain the flow characteristic inside the human lung. The result then not only can aid the
medical team by providing the solution for treatment but also can initiate to the new
technology for medical instruments.
1.2
Objectives
The objective of the study is to determine the effect of stenosis in different
locations in trachea to the flow and pressure distribution.
3
1.3
Scope
a) Actual image will be used
b) Numerical modeling will be use for analysis
c) Effect of the stenosis location will be considered
4
CHAPTER 2
LITERATURE REVIEW
2.1
Overview of human respiratory system
Respiratory system is one of the essential systems for all organisms and the
function of this system is to allow gas exchange to all parts of the body. Each cell in the
body will receive the oxygen (O2) and release the carbon dioxide (CO2). The structure of
the gasses exchange or the anatomy of the respiratory system is different depending on
the organisms. For human, the respiratory system can be separated into two major parts
which is an upper respiratory region and the lower respiratory region.
The upper respiratory region comprises the nasal passages, pharynx, and the
larynx while the lower respiratory region includes the trachea, the primary bronchi and
lungs. Lungs and linked blood vessels deliver oxygen to entire body and remove carbon
dioxide from the system. Normally, the left lung is smaller than the right lung as heart is
located in the right lung region.
5
Figure 2.1 Respiratory system
(www.lakesidepress.com, 2008)
2.2
Trachea
Trachea is the tube that connects mouth and nose to lungs. It located in the front
of neck and the end of the larynx. The trachea has rings called cartilages for support and
it is similar to the rings in the vacuum cleaner host. The air will passes through the
trachea while the food and drink go down a different tube called esophagus which
located behind the trachea.
6
The larynx goes directly into the trachea or the windpipe. For adult, the trachea
is a tube approximately twelve centimeters in length and two point five centimeters
wide. The trachea is kept open by rings of cartilage within its walls. Similar to the nasal
passages, the trachea is covered with a ciliated mucous membrane which brushes debris
up and out. This tissue destroyed by smoking but can regenerate if the person stops
smoking. At the end of trachea, it divided into two main bronchi (left and right), one to
each lung.
Figure 2.2 Trachea and major bronchi of the lungs
(Encyclopedia Britainnica,Inc,2008)
7
Figure 2.3: Normal bifurcation (Zuhairi, 2009)
2.3
Trachea stenosis
Breathing difficulties can be caused by many factors. One of the factors is the
restriction of the main trachea. This restriction will alter the flow path of the inhaled and
exhaled air and subsequently change the behavior inside the trachea. Therefore, it is
important to understand the changes of the flow behavior along with the pressure
distribution with respect to the presence of stenosis or obstruction in the trachea.
Spittle (2000) suggested that tracheal stenosis presents as shortness of breath and
the symptoms do not usually occur at rest until the trachea has stenosed to 30% of its
original size. Yang (2007) has shown that long-segment stenosis due to congenital factor
is very critical especially for infants and showed that the removal of the stenosis
managed to remove the breathing problem. Hammer (2004) recommended that correct
8
diagnosis will need additional information in order for medical practitioners to perform
proper diagnosis.
Figure 2.4: Obstructive airway (Zuhairi, 2009)
Figure 2.5: Tracheal stenosis (source from www.bidmc.org, accessed on 3rd of
November 2009)
9
2.4
Trachea stenosis effect to velocity and pressure distribution.
Apart from understanding the flow, another critical factor that is affected by the
presence of stenosis is the pressure distribution. Brouns (2006) have completed an
extensive numerical study on the pressure drop along the trachea. Brouns used artificial
stenos in his study where the stenos were patched to a healthy airway. The model was in
three-dimensional. Brouns results showed that the overall pressure drop at rest was only
affected in case of severe constriction. The results also hinted that the pre-critical stage
can be detected using the computed pressure drop
The effect of the increasing size of the stenosis also was investigated by Jayaraju
(2006) in their research and they found out that the pressure drop shows modest
increases with the degree of narrowing up to 75% constriction. On the other hand,
Cebral (2004) research showed decreased pressure and increased shear stress in the
region of a stenosis besides an increased flow velocity during inspiration.
2.5
Effect of the stenosis location to the flow characteristic
Moreover, the locations of the tracheal stenosis vary from patients to patients.
Freitag (2007) suggested five common locations of tracheal stenosis. Other researchers
have chosen locations around these three sections first section which is upper, middle
and lower third of the trachea. Jayaraju (2006) modeled the flow for patient-specific case
where the location of the tracheal stenosis is at the upper third of the trachea only.
However, Lam used a model of trachea stenosis at the lower third of the trachea to assess
the accuracy of three-dimensional (3D) CT-image scan and virtual bronchoscopy. The
10
purpose was to apply the knowledge to the treatment for infants and children that having
the tracheoesophageal fistula and tracheal stenosis. But no flow analysis was done.
Figure 2.6: Suggested location for tracheal stenosis (Freitag et al.(2007), A
proposed classification system of central airway stenosis, European Respiratory
Journal)
2.6
Actual modeling
While many researchers use simplified geometry of the trachea, there are many
others who use patient-specific images to study the flow inside the trachea. Both
11
geometries have different advantages and disadvantages. The importance of using actual
images as a model to study the flow pattern in the trachea with stenosis is very crucial.
Some researchers used simplified model to obtain the flow conditions. However, Russo
(2008) confirmed that the effect of cartilage rings increased with increased flow rate in
the trachea. Therefore, by using actual images, the effect of this cartilage rings will be
imbedded in the flow study
Figure 2.7: Example of trachea model without stenosis.
(a) actual model (b)simplified model
Detailed patient-specific flow pattern using actual image was also obtained by
Choi (2006) where flow separation due to sudden change in diameter was observed in
the main trachea. Another actual image flow model studied by other researchers such
that completed by Lin (2007) where turbulence induced by the laryngeal jet was shown
to affect the airway flow pattern significantly. Sun and Yu (2007) claimed that using the
12
actual images, the models precisely preserve the original configuration and the results of
the pressure and velocity distributions in the airflow field are accurately determined. It
shows that pressure gradients of airway are lower for the healthy person and the airflow
distribution is quite uniform in the case of free breathing. Further study regarding the
flow using an actual model conducted by Gemchi (2007) demonstrated that the nature of
the secondary vortical flows which develop in such asymmetric airways varies with the
specific anatomical characteristics of the branching conduits.
2.7
Current study
In this study, the effect of several locations of the stenoses to the air flow inside
the trachea is investigated. Three locations of stenoses were chosen, namely upper,
middle and lower third of the trachea. These choices follow the suggestion by Freitag
(2007). This study will show the effect of these locations to the pressure drop as the flow
enters the bifurcations. Critical stenos location such as near the bifurcation is also
expected to alter the flow rates into the bifurcation which is one of the major
contributions of this study. Actual images from CT scan were obtained and conversion
to numerical modeling was made. The numerical study of the flow was then presented.
13
CHAPTER 3
METHODOLOGY
3.1
Introduction
To achieve the objective of the study, several steps were used in order to
accomplish the good results. In this study, one of the Computational Fluid Dynamics
(CFD) software called Engineering Fluid Dynamics is used. This software simulates the
flow inside the human airways using the actual model. Before the model can be
simulating, it previously has been prepare using the Mimics software to get the actual
geometry inside the human airways.
Using several boundary conditions, the actual model then has been simulate
using a few different flow rate to get the result of the flow characteristics inside the
human airways. The details will be described in this chapter.
14
3.2
Simulation model
There are two option of model that can be used to simulate the flow inside the
human airways. One is using the simplified model where the model is draw back using
the same geometry as the actual airways. But, due to the complexity of the actual human
airway geometry, usually it will be simplified into the symmetric or asymmetric model
(Luo,X.Y el at ,2004, Russo. J et al, 2008).
The other option is using the actual model where it been processes from the CTscan images. The results from the analysis using the geometry of the scan-based have
verified their consistency with measures from previous anatomic studies (Tawhai, M.H.
et al, 2004). The actual complexity of the human trachea geometry and the location of
stenosis inside the trachea did influence the accuracy of the distribution in velocity and
pressure inside the human airways.
To compare the difference that occurs in each circumstance, four separate
tracheas and main bronchi models were created anatomically: (a) a healthy model
without stenosis and (b) three other models with different locations of stenosis along the
trachea (Figure 3.1). To evaluate the result from each model side by side, the major
geometries were retained for every model and only the stenosis area were manipulate to
create the other models. Toward reconstruction of the CT models, a few steps need to be
done.
155
Stenosis
locationns
(ii)Model no.1
(ii) Model
M
no.2
(iii)Modeel no.3
(iiv)Model no
o.4
H
Healthy moddel Stenosiis location 1 Stenosis location 2 Stenosis location 3
Figure 3.1 Four sep
parate mod
del of trach
hea and maain bronchii
ges from onee
Thhe models arre based onn the Compuuted Tomoggraphy (CT)) scan imag
Chinese addult male patient, 60 years old as the referencce stenosis m
model (Figu
ure 3.1 (ii))).
The locatiion of the sttenosis is loocated at thee upper thirrd of the trachea. The stenos
s
of thee
same moddel then haad been rem
moved to generated
g
thhe healthy model andd artificiallyy
relocated aat different locations for
f the other two stenoosis (Figure 3.1 (iii and
d iv)) wheree
the locatioon is at thee middle annd lower thhird of the trachea ass suggested
d by Freitagg
(2007). The CT scan
n images weere taken in the axial pllane with a resolution
r
of
o 512 x 5122
kness of 1mm
m. AMIRA
A, one of thee conversion software was used too
pixels andd slice thick
convert thhe CT-scann images thhat in the D
DiCom form
mat into soolid three dimensiona
d
al
models. Smoothing
S
of the surfface was peerformed too eliminatee the rough
hness of thee
curves cauuse by partiaal volume effects,
e
Spirrka (2005).
16
To extract the respiration model image and to remove other unrelated region that
comprise in the CT-scan images taken, threshold separation range in between -1024 and
-500 was used to get the air region. Then the respiration model was obtained by using
region growing function where the voxels within the airway lumen were identified.
Figure 3.2: 3D model of the whole respiration system reconstructed from CT-scan
images
The model then went through the cutting and removing process to separate the
other respiration organs until only trachea and main bronchi remain as the solid model.
The completed model then underwent the 3D calculation after the Morphology and
Boolean operation where the anatomical wall created. Next, the model been export to
another software package called MAGICS. Here, major alteration such as removing and
relocating the stenosis, geometries correction and holes patching been done. Refined
model is then saved in ASCII STL format and the numbers of faces are reduced to 15000
17
7
d to limittation of thee EFD softw
ware that beeen used to simulate
s
thee
faces usingg AMIRA due
model.
(a)
(b)
Figure 3.3: (a) Acctual tracheea model exxtract from
m the wholee respiration system
(b
b) Actual trrachea mod
del ready too be simulaated
3.3
Booundary Coondition
Byy using SOL
LIDWORK
K 2008 softw
ware, the STL
S
formatt model waas converted
d
into SLDP
PRT formatt and the bo
oundary conndition for every inlet and outlet are defined
d.
Flow ratess defined in
n each cases are comp
puted based on flow paartition ratio
on given by
y
18
Horsfield where 55% of inlet flow rates diverges into right bronchus while the other
45% to the left bronchus. The condition imposed on the inlet and outlets are summarized
in Table 3.1.
Table 3.1 Parameters at all trachea model for three different breathing conditions
Parameter
Incompressible flow
Flow rate (l/min)
15,60 and 100
Inlet Pressure
101325 Pa
Density
1.225 kg/m3
Viscosity
1.7894e-05 kg/ms-1
The wall model is assumed as smooth and rigid wall due to the realistic condition
inside the trachea where the wall is covered with cilia and mucus which tends to make
the wall area smooth and the cartilage rings that support the trachea makes the trachea
rigid. In addition, the flow inside the human lung airway is taking as non-slip condition
and the air was assumed to be a homogeneous. Besides, due to the speed of air taken is
slower than the speed of sound, the air is assume as incompressible flow and the
temperature together with density are constant (Luo,X.Y el at, 2004).
M = V/C
where:
V = velocity of flow
C = velocity of sound
19
3.4
Governing Equations
Same as other fluid flow simulation, the following equations were applied
to the actual human airways model. It is based on the Navier-Stokes equation.
Continuity equation
0
Momentum Equations
Reynolds Number
The equation use to determine the flow type whether it is laminar or
turbulent. The parameter that used to determine the Reynolds Number are
density, ρ, velocity, u, length of flow, D and viscosity of the fluid, μ.
20
3.5
K-ε turbulent model
In the CosmosFloWork software, there are built in K-ε turbulent model
which is used to analyze the turbulent case.
For turbulent kinetic energy k,
For dissipation e,
2
where the value constants are;
1.44,
1.92,
1.0,
1.3
21
3.6
Summary of the methodology throughout the process
CT scan data
• Get the CT-scan data of the trachea patient from hospital.
Process the data to built the actual model
• Raw CT-scan data reconstruct using Mimics software to rebuilt
the actual trachea model.
• Preparing the actual model and export to Solidworks software.
• From solidworks, choose CosmosFloWorks to run the
simulation after fill in all the parameters and boundary
condition
Getting the results
• Process the results obtain for better presentation
22
CHAPTER 4
RESULT AND DISCUSSION
4.1
Overview
Using Engineering Fluid Dynamics software, all models then been simulated.
The result shown in this study comprises the data from the healthy and also three other
stenosis trachea models. The purpose is to study the effect of the stenosis in the different
location (upper, middle and lower third of trachea) in flow characteristic and pressure
distribution in human airways. The results of the simulation will be cover for three
different values of flow rates which are 15 l/min, 60 l/min and 100 l/min. Besides, the
risk in breathing problem due to the stenosis and stenosis location will be discuss in this
chapter.
23
4.2 Velocity distribution
The asymmetrical geometries of the trachea that was extracted from the CT-scan
are contributes to the complexity of the flow pattern inside the human airways. This
creates the imbalanced flow rate distribution all the way through the bronchus. Figure
4.1, Figure 4.2 and Figure 4.3 shows the influence of the stenosis location and the flow
rate induced at the inlet to the velocity distribution along the human airways. It
illustrated the comparison between the healthy models with the other three models with
different location of stenosis for three values of flow rates represent the resting activity,
regular activity and heavy exercise.
Graph V/Vo vs Length for Q15
Healthy Trachea
Stenosis Trachea 1
Stenosis Trachea 2
Stenosis Trachea 3
4
3.5
3
V/Vo
2.5
2
1.5
1
0.5
0
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
m
Figure 4.1: Central velocity distribution of each model in Q=15 l/min
24
Graph V/Vo vs Length for Q60
Healthy Trachea
Stenosis Trachea 1
Stenosis Trachea 2
Stenosis Trachea 3
4
3.5
3
V/Vo
2.5
2
1.5
1
0.5
0
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
m
Figure 4.2: Central velocity distribution of each model in Q=60 l/min
Graph V/Vo vs Length for Q100
Healthy Trachea
Stenosis Trachea 1
Stenosis Trachea 2
Stenosis Trachea 3
4
3.5
3
V/Vo
2.5
2
1.5
1
0.5
0
-0.02
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
m
Figure 4.3: Central velocity distribution of each model in Q=100 l/min
25
The flow enter the inlet of the trachea as the flow rates induced and having
almost the same pattern for each cases where the stenosis located at the different
location. After that it starts to accelerated at the stenosis area for each models with
stenosis except for the healthy model due to the existing constriction of the crosssectional area.
For the first location of stenosis, the gap between the patterns of the velocity
throughout the trachea is almost the same as the healthy model except at the stenosis
area for each flow rates used at the inlet. The velocity flow speeds up at the stenosis area
and slows down just about the same pattern again as the healthy model before it reach
the branches where the flow divided into right and left bronchi. It is different with the
second and the third location of the stenosis. The result shows a huge different in
velocity of the flow after downstream the stenosis area compared to the healthy model.
Distance between the stenosis and bifurcation area and the localized disturbance
originated at the geometries features such as the curvenature etc leads to dissimilar flow
pattern.
Since of the length between the stenosis and the bifurcation area for the second
stenosis is shorter than the first but longer than the third location, some transformation
on the velocity distribution still appears after the stenosis area but it is still not enough to
reduce the velocity before it reach the inlet of the branches. Same situation applies o the
third location but in this case, the velocity of the flow is still in high speed when it
reaches the bifurcation area and it significantly influences the distribution of the flow
rate to each bronchus, left and right. Overall, the velocity patterns for every case it not
changing radically every time the flow rate is changed. The lower stenosis results in the
biggest velocity difference at the bifurcation area as compared to that of the healthy
model followed by the middle and the upper stenosis location.
26
4.3
Pressure Distribution
The following figures show the pressure distribution from the inlet at the top of
the trachea to the outlet at both right and left bronchi for every models and flow rates.
The lines plotted represent the pressure at the centerline of the studied model. It can be
seen that pressure drop is increasing as the flow passes through the stenosis area. The
value of the pressure drop is neglected and only the pattern of the characteristic is
emphasized in this study. Therefore, the graphs plotted in dimensionless unit for each
models and flow rates.
1.001
P/Po
Graph P/Po vs Length for Q15
1.0005
1
0.9995
0.999
0.9985
0.998
0.9975
0.997
0.9965
Healthy Trachea
Stenosis Trachea 1
Stenosis Trachea 2
Stenosis Trachea 3
0.996
0.9955
0.995
0.9945
m
0.994
0
0.02
0.04
0.06
0.08
0.1
0.12
Figure 4.4: Central pressure distribution of each model in Q=15 l/min
0.14
27
7
d
lenngth measurred from the inlet. For the stenosiss
Eaach stenosis located at different
located at the upper third
t
of the trachea, the distance of
o the stenoosis is appro
oximately at
a
37mm from the inlet. The secon
nd and the third
t
locatio
on were aroound 57mm
m and 87mm
m
w generatted from thee same sourrce, the bifu
urcation areaa
respectiveely. Since alll models were
calculated
d from the in
nlet is the saame and it is
i around 11
10 mm from
m the inlet. From
F
Figuree
4.4, it can
n be seen th
hat the low
w flow rate, 15 l/min that
t
is impo
osed at the inlet of thee
trachea do
oes not show
w a significcant effect w
when the lo
ocation of thhe stenosis s changing
g.
The pressu
ure drop alo
ong the tracchea are so small for each
e
model of the sten
nosis tracheaa
compared to the healthy modeel even thee location of the stennosis is neearer to thee
bifurcation
n area. Theerefore, the patient diaagnosed witth stenosis in the trach
hea will no
ot
have a breeathing prob
blem when they
t
in restiing conditio
on.
1.001
P/Po
Graph P/Po vs Leength for Q60
Q
1.0005
1
0.9995
0.999
0.9985
0.998
0.9975
0.997
0.9965
Healthy Traachea
Stenosis Traachea 1
Stenosis Traachea 2
Stenosis Traachea 3
0.996
0.9955
0.995
0.9945
m
0.994
0
0.02
2
0.04
0.06
0.08
0.1
0.1
12
0.14
Figgure 4.5: Central
C
presssure distriibution of each
e
modell in Q=60 l//min
0.16
28
8
ure 4.5, thee effect of th
he differentt stenosis loocations to the
t pressuree
Ass of the Figu
along the trachea staarted to sh
how clearly when the flow rate stimulated at the inleet
increase too 60 l/min. Pressure drrop betweenn the inlet an
nd the bifurrcation areaa for the firsst
location of the stenossis illustratees a small difference
d
ass comparedd to the seco
ond location
n
of the sttenosis evaaluated with
h the heallthy modell. The diffference beccome moree
significantt when the same flow
w rate inducced at the inlet of thee third locaation of thee
stenosis where
w
the lo
ocation is nearest
n
to th
he bifurcation area aree compared against thee
other two stenosis mo
odels. This circumstannce happenss for the reaason that the differencee
in distance between the stenosiss with the bbifurcation area did afffect the prressure afterr
hrough the stenosis.
s
Ass for stenosee located at the upper tthird of the trachea, thee
passing th
length bettween the sttenosis and
d the bifurcaation area is
i long enouugh for the pressure to
o
rise back after
a
passin
ng through the
t stenosiss area. So, as
a the lengthh shortens, the chancess
for the preessure to inccrease are lo
ower. It lead
ds to the hig
gher pressuure drop for the stenosiss
located neearer to the bifurcation.
b
P/Po
1.0
001
1.00
005
1
0.99
995
0.9
999
0.99
985
0.9
998
0.99
975
0.9
997
0.99
965
0.9
996
0.99
955
0.9
995
0.99
945
0.9
994
-0.02
Graph P
P/Po vs Len
ngth for Q1100
Healthy Trachea
Stenosis Trachea 1
Stenosis Trachea 2
Stenosis Trachea 3
m
0
0.02
0.04
0
0.06
0.08
0..1
0.12
2
Figgure 4.6: Ceentral presssure distrib
bution of each model in Q=100 l/min
l
0.14
29
The flow rate then increase to 100 l/min and the result in pressure distribution
along the trachea are plotted as in figure 3 (c). As seen in the figure, the pressure drop
between the inlet and the bifurcation in all models is higher as compared to the 15 l/min
and 60 l/min flow rates. Although the first stenosis location shows a bigger pressure drop
compare to the previous flow rates, the second and the third location illustrate more
significant differential when the flow rate increases. Moreover, the complex geometries
that comply in the models structure also influence the pressure drop along the trachea
due to the curvature, angle etc. It follows the Bernoulli and Continuity equations. As a
result, if the stenosis located at the first location, the pressure drops is still not so severe
even if the flow rate increases. It is because, the distance of the stenosis is far from the
bifurcation and it give the pressure enough time to regain the approximate original value
as before it undergoes the stenosis area. However, for the second and the third location,
severe pressure drop is shown as the flow rate increase and it indicate the risk to the
breathing problems. The pressure distributes to both right and left bronchi are at the
lower state due to this higher pressure drop.
4.3.1
Risk due to location of stenosis.
Figure 4.7 shows the differences between the inlet and bifurcation area of P/Po at
every location of stenosis and also for every flow rates that induced at the every inlet of
the model. The values plotted taken from the proximal of the trachea to the
bifurcation area. From the figure, as the location of the stenosis located nearer the
bifurcation area, the range of the maximum and minimum P/Po is increasing. This
increment shows that the pressure drops is higher as the location is nearer to the
bifurcation area. As the result, the difficulty in breathing problem will also increase as
the pressure drop higher.
30
The graph also shows that, the difference in pressure drop is more significant
when the flow rates increase and the stenosis that is nearer to the bifurcation area is the
most affected as the flow rates changes. It can be used to indicate the risk in breathing
problems for patient that is diagnosed with stenosis inside the trachea.
ΔP/Po (P/Po imlet - P/Po bifurcation area)
Range of P/Po between inlet and bifurcation area for each location of stenosis
and flow rates
0.0045
0.004
0.0035
0.003
0.0025
HEALTHY
0.002
STENOSIS 1
0.0015
STENOSIS 2
0.001
STENOSIS 3
0.0005
0
0
15
30
45
60
75
90
105
120
Flow rates, Q (l/min)
Figure 4.7: Range of P/Po between inlet and bifurcation area for each location of
stenosis and flow rates
Using the data plotted in Figure 4.7, the risk indicator for stenosis effect as the
location located nearer to the bifurcation is calculated. The data from the range of
pressure drop between the inlet and bifurcation area (ΔP/Po) for each model then been
compared to the healthy model to obtain the different risk between the health condition
and the condition with several location of stenosis. Hence, the effect of the stenosis can
been group as severe or mild to the respiratory system.
31
Risk of stenosis for every location and flow rate
0.003
0.0025
ΔP/Po
0.002
Healthy
0.0015
Stenosis #1
0.001
Stenosis #2
Stenosis #3
0.0005
0
0
20
40
60
80
100
120
Flow rate, Q (l/min)
Figure 4.8: Risk of stenosis for every location and flow rate
Next, the risk effects from stenosis at every location were plotted in Figure 4.8.
As of the graph illustrate, the healthy model did not have any difficulty even if the
person having a heavy exercise. However, the first location of the stenosis start to show
the effect of the stenosis when the flow rate increase compared to the healthy model but
the risk is still low since the difference compared to the healthy is small. For the second
location of the stenosis which is at the middle third of the trachea, the risk is mild for the
lower flow rate but rise for heavy activity. It can be dangerous for several patient based
on their condition. For both first and second location, the patient possibly need only
inhaled type of treatment and can avoid the dissect treatment. In contrast with the third
location of the stenosis, the regular activity already caused severe risk to appear and
patient with this location of stenosis maybe need stent as the solution for their breathing
problems.
32
Thus, the utmost risk for breathing problem emerges when the stenosis is located
at the lower third of the trachea and the patient doing heavy exercise where the air flow
rate that going into the airways is around 100 l/m. The pressure gradient in this case is
the highest compare to others cases.
33
CHAPTER 5
CONCLUSION
The airflow within patien specific geometry of human airway derived from CTscan image is numerically studied using the Engineering Fluid Dynamics (EFD)
software. The flow and pressure distribution as well as the characteristics all through the
trachea are examine in details in this study. Using different models those represent
healthy and other stenosis models with different stenose location, several conclusions are
drawn.
The results obtain using the CT-scan images shows more complicated flow
pattern and also higher in pressure drop compared to the simplified model. This is due to
the complexity of the geometries of the model and also the branching angle of the
bronchus at the end of the bifurcation area that leads to the uneven pattern in velocity
and pressure distribution in every model. From these results, it is confirmed that every
patient will results in different pattern of the flow characteristic due to the different
geometries of their trachea.
34
Then, when the stenosis is added to the healthy trachea, the flow pattern
illustrated in the results show the disturbance especially at the stenosis area and also at
the bifurcation area compared to the healthy model. The velocity started to increase
where the stenosis located and reduce back before reach at the branches for the stenosis
model results. The differential is more significant when the location of the stenosis is
relocated at another two location where the stenosis positioned nearer to the bifurcation
region.
As the risk indicator plotted, the consequences for the different flow rates
induced at the inlet are emphasized. It show that, stenosis at the upper third of the
trachea, if the flow rates increase from 15 l/min to 100 l/min, it still can be consider as
mild breathing problem because the pressure drop between the inlet and the bifurcation
area is small and approximately similar to the healthy model. For the other two location
of the trachea, the flow rates used at the inlet did affect the respiration flow significantly
and it leads to the breathing problems. For some cases, if the patient that diagnoses with
this kind of stenosis, it can be categorized as the severe breathing problems because the
pressure drop at the branches is higher and it did influence the distribution of flow to
both two bronchi, left and right.
:
As a conclusion, the results can be summarizing as follows:
1. As stenosis located at the upper third of the trachea, the pressure drop along the
trachea are insignificant in every breathing condition but differ to the velocity
where the maximum velocity is increase as the flow rate increase.
2. For stenosis located at the lower third or the trachea, both pressure drop and
velocity did effect clearly as the flow rate increase.
35
3. The effect of different location of the stenosis on the velocity distribution along
the centerline shows similar increment in every flow rate.
4. The risk in breathing difficulties if the patient having a stenosis at the third
location is three times higher compare to the first location if the patient in resting
condition. It increases to five times higher when doing the regular activity and
eight times higher if the patient doing heavy exercise. The comparison is based
on the same size of the stenosis.
36
References
1. Brouns, M., Jayaraju, S. T., Lacor, C., Mey, J. D., Noppen, M., Vincken, W., et al. (2007).
Tracheal stenosis: a flow dynamics study. J Appl Physiol , 102: 1178-1184.
2. Calay, R. K., Kurujareon, ,. J., & Holdo, A. E. (2002). Numerical Simulation of Respiratory
Flow Patterns within Human Lung. Elsevier , 130:201-221.
3. Cebral, J., & Summers, R. (2004). Tracheal and central bronchial aerodynamics using
virtual bronchoscopy and computational fluid dynamics. Medical Imaging , 8:1021 1033.
4. CHOI, L.-T., & TU, J. (2007). FLOW AND PARTICLE DEPOSITION PATTERNS IN A REALISTIC
HUMAN DOUBLE BIFURCATION AIRWAY MODEL. Fifth International Conference on CFD
in the Process Industries , 19:117–31.
5. Freitag, L., Unger, M., Ernst, A., Kovits, K., & Marquette, C. (2007). A proposed
classification system of central airway stenosis. European Respiratory Journal .
6. Gemci, T., Ponyavin, V., Chen, Y., Chen, H., & Collins, R. (2007). CFD Simulation of
Airflow in a 17-Generation Digital Reference Model of the Human Bronchial Tree.
Biomechanics .
7. Guan, X., & Martonen, T. B. (2000). FLOW TRANSITION IN BENDS AND APPLICATIONS
TO AIRWAYS. J. Aerosol Sci , 31: 833-847, .
8. Hammer, J. r. (2004). Acquired upper airway obstruction. PAEDIATRIC RESPIRATORY ,
5:25–33.
9. Heged´us, C. J., Balásházy, I., & Farkas, Á. ( 2004). Detailed mathematical description of
the geometry of airway bifurcations. Respiratory Physiology & Neurobiology , 141:99–
114.
10. Jayaraju, S. T., Brouns, M., Lacor, C., Mey, J. D., & Verbanck, S. (2006). EFFECTS OF
TRACHEAL STENOSIS ON FLOW. European Conference on Computational Fluid Dynamics
.
37
11. Lam, W. W.-m., Tam, P. K., Chan, F.-L., Chan, K.-l., & Cheng, W. (2000). Esophageal
Atresia and Tracheal Stenosis:Use of Three-Dimensional CT and Virtual Bronchoscopy in
Neonates, Infants, and Children. American Roentgen , 174:1009–1012.
12. Lin, C.-L., Tawhai, M. H., McLennanc, G., & Hoffmanc, E. A. (2007). Characteristics of the
turbulent laryngeal jet and its effect on. Respiratory Physiology & Neurobiology ,
157:295–309.
13. Luo, X. Y., Hinton, J. S., Liew, T. T., & Tan, K. K. (2004). LES Modeling of Flow in a Simple
Airway Model. Medical Engineering and Physics .
14. Russo, J., Robinson, R., & Oldhamb, M. J. (2008). Effects of cartilage rings on airflow and
particle deposition in the trachea and main bronchi. Medical Engineering & Physics , 30:
581–589.
15. Spittle, N., & McCluskey, A. (2000). Tracheal stenosis after intubation. PubMed Central ,
321(7267): 1000–1002.
16. Yang, J. H., Jun, T. G., Sung, K., Choi, J. H., Lee, Y. T., & Park, P. W. (2007). Repair of
Long-segment Congenital Tracheal Stenosis. J Korean Med Sci , 22: 491-496.
38
APPENDIX A
Title/Week
Project Plan
Literature Review
Mimics Tutorials
Model Development
Initial Simulation
Analysis results
Draft Preparation
Slide Preparation
Title/Week
Project Plan
Models development
Simulation
Analysis results
Draft Preparation
Paper preparation
Slide Preparation
Gantt Chart for Master Project 1
1 2 3 4 5 6 7
8
9
10
11
12
13
14
Gantt Chart for Master Project 2
1 2 3 4 5 6 7
8
9
10
11
12
13
14
39
APPENDIX B
Velocity and Pressure Contour along Trachea
Velocity
Q15
Healthy Model
Stenosis #1
Stenosis #2
Stenosis #3
40
Q60
Healthy Model
Stenosis #1
Stenosis #2
Stenosis #3
Q100
Healthy Model
Stenosis #1
Stenosis #2
Stenosis #3
41
Pressure
Q15
Healthy Model
Stenosis #1
Stenosis #2
Stenosis #3
Stenosis #1
Stenosis #2
Stenosis #3
Q60
Healthy Model
42
Q100
Healthy Model
Stenosis #1
Stenosis #2
Stenosis #3
43
APPENDIX C
44
Simulation of stenosis effect on airflow
pattern in trachea and main bronchi
Z.M.Salleh1, N.H.Johari2, K.Osman, Juhara, Rafiq
1
Faculty of Mechanical and Manufacturing Engineering,
Universiti Tun Hussein Onn Malaysia,
86400 Batu Pahat,Johor
Malaysia
E-mail : zulia@uthm.edu.my
2
Faculty of Mechanical Engineering
Universiti Malaysia Pahang
26600 Pekan, Pahang
Malaysia
Faculty of Mechanical Engineering
Universiti Teknologi Malaysia,
81310 Skudai, Johor, Malaysia
Abstract—Tracheal stenosis is a condition where
the diameter size of trachea wall decreases and
leads to the obstruction of the breathing airflow.
Investigation on the effect of the stenosis to the
airflow pattern in the trachea and main bronchi is
the objective for this study. CT-scan images of two
airways models were modeled, one with the
stenosis and one without. Numerical solution was
used to study the airway pattern inside the airway.
Different boundary conditions of inspirations flow
rate were applied; 15 l/min, 60 l/min and 100l/min
where the ratio for the right main bronchus is 55%
and for the left main bronchus is 45%. The results
showed that the pressure drop inside the stenosis
model is higher compared to that of healthy model.
The pressure drop was also shown to interrupt the
inlet condition into the main bronchi.
Keywords- Trachea, main bronchi, CT-scan
images, simplified model and respiratory
system.
Introduction
Knowledge about airflow in human airways
was known as the alternative source that helps in
treatment for the breathing patients. The
treatment for the respiration disease usually in
the form of aerosol that delivered into the lung
and the efficiency of the treatment is depends on
the percentage of the drug particle received by
the lung.
Tracheal stenosis is one of the tracheal
symptoms that obstruct the airways path and
lead to breathing difficulties. Thus, present
study aims to explore the flow dynamics inside
the actual abnormal trachea which are suffering
of stenosis. Ideally, the flow pattern would be
different and inconsistent compared to healthy
trachea.
The very straight way to understand the
airflow characteristics are to study its pressure
drop and velocity field along the tracheabronchial region. Numerous numerical studies of
inhaled airflow and particle transport modeling
have been performed until now. Schroter and
Sudlow [1] initiated the earliest study of airflow
inside the human lung. Their experimental study
of single symmetric bifurcation and flow was at
Reynolds numbers ranging from 50 to 4500
concluded that the inhale flows were
independent on either Reynolds number and
entry velocity profiles. It was followed by other
studies which address varieties of airflow and
particle deposition problems in selected segment
at bifurcation, main bronchi and lower
generations [2-6]. They have shown that
simulation of airflow and particle transport at
different bronchi’s generation with different
boundary conditions resulting significant
changes of velocity and pressure drop which
influenced the breathing cycle. However, all the
research named above was used simplified
45
model of human lung due to the limitation of
applications. Their findings and conclusions
were initiated this present study to go deeper on
investigation of air flow dynamics patterns in
actual human lung model.
Besides, studies on airflow and particle
deposition inside abnormal trachea specifically
have received relatively small numbers. In 2006,
Mark Brouns et al. [7] made the earliest study of
Computational
Fluid
Dynamics
(CFD)
simulations within model of stenosis trachea.
They initiated a study of flow dynamics inside a
few sizes of stenosis and found that pressure
drop dramatically increased due to the
constriction of trachea airways and concluded
that the pressure drop can be detected at early
stage of stenosis. Although Mark Brouns et al.
simulated airflow inside a few conditions of
model geometry and boundary condition, the
results produced still can be argued. It is because
the model used have smooth wall, no rings
protrusions effect, and only shows flow pattern
until centre of trachea. We believed that the
actual wall conditions, shapes, angle of bending,
bifurcation of main bronchi and all the boundary
conditions are a priority in analyzing the effect
of stenosis on air flow inside trachea.
In this study, two actual models of trachea are
used; with and without the stenosis. The flow
pattern in healthy trachea is benchmark to the
stenosis trachea. Dimensionless techniques were
used along the way of analyzing the result.
Methodology
A. The model geometry
The complexity of the actual airway geometry
is essential in improving the efficiency of
simulation airflow to capture the velocity
distribution and pressure drop. For this study,
two models with different geometry conditions
were utilized for comparison purpose (figure 1).
The models were reconstructed from the
Computed Tomography (CT) scan images by
using modeling software before being exported
into Computational Fluid software for simulation
of airflow. The images of the reconstructed
model of human airways consists of trachea and
main bronchi were taken from an Asian, 60
years old male as for stenosis model and the
stenosis area for the same model then been
removed to used as the healthy model.
Smoothing of the surface was performed on the
model to eliminate the roughness of the curves
caused by partial volume effects and pixilation
of rounded images [8]. The model provides an
anatomically realistic model of human airways
Figure 1: The extracted actual model of
trachea and main bronchi from CT
images. Healthy model (left) and
abnormal trachea with constriction of
stenosis model (right).
B. Boundary conditions
Beside the model geometry, boundary
conditions are another factor that needs to be
looked while studying the airflow [2]. Laminar
flow does not occur in human lung airways
except in very small airways deep down into the
lung at resting condition [9]. The airflow from
larynx to third generation is transitional-toturbulent even at a low local Reynolds number.
The turbulence may be induced again at the
central zone due to flow instabilities generated
by the great geometric transition at the carinal
ridges which may complicate flow structures
[10] have shown that the turbulent influenced the
particle deposition. Higher particle deposition
was recorded for turbulent flow over laminar
flow [11]. Thus, the turbulence generated by the
larynx need to be taken into account. K-epsilon
model is appropriate to simulate internal
laminar-transitional-turbulent flow. The actual
model wall was assumed as smooth and rigid
wall along the airways. In the actual trachea, the
wall actually covers by cilia and normally lined
up with mucus which tends to make it smooth. It
is also have the cartilage rings to support the
trachea.
The airflow in healthy and stenosis human
airways is to be solved using k-epsilon model.
46
The k-epsillon was empployed as paart of the
consideratioon for occurrennce of turbuleent flow at
low Reynoldds numbers as
a a result of shear
s
flow
and its proven ability too simulate thhe airflow
[12]. A commercial finite-volum
me based
software Enngineering Fluid
F
Dynamiics (EFD)
was deployeed to solve stteady state conservation
of mass andd momentum equations in all cases.
The EFD iss capable of solving
s
turbullent model
by employinng a finite-vollume method.. The flow
rates imposeed at the outlets are compuuted based
on flow parrtitioning ratiion given by Horsfield
[13] where 55% of inlet flow rates diiverge into
right broncchus while 45%
4
of flow into left
bronchus. The
T conditionss imposed on the
t outlets
are summariized in Table 1
b
trachea model
m
for
Table I: Parrameters at both
three differeent breathing conditions.
c
Parameeter
Flow raate
(l/min)
Inlet Prressure
Densityy
Viscosiity
Incompressible
flow
15,60 and 100
101325 Paa
1.225 kg/m
m3
1.7894e-055 kg/ms1
area after the stenosis is locateed. The
gnificant
difference became more sig
when the flow rate increases ass shown.
The diffferences aare due to the
obstructionn and redduce sizes of the
trachea diiameter at the stenosis and it
affected thhe flow from
m moving smoothly
s
to the main
m
bronchhi. The flo
ow that
reaches to each side oof the main
n bronchi
also effeccted when the differeent flow
rates were applied intto both mod
del.
Then again, for the velocity co
ontour, it
started to show diffferences in contour
when appplying the 60 l/min and
a
100
The
l/min booundary cconditions.
contours are
a more uuniform thrroughout
the tracheea and maiin bronchi for the
healthy model
m
compaared to the stenosis
model. For the steenosis mod
del, the
velocity fllow happeniing to distraact when
reach the obstructioon and staarting to
speed up before
b
it beecame unev
ven. But
the locatioon of the sstenosis itseelf is far
enough foor the veloocity to refform the
uniform profile bbefore reaach the
bifurcationn area.
(a) 15 l/m
min
Re
esult and Discussiion
A. Pressurre and veloccity contourrs
The veloocity and thhe pressuree contour
throughouut the trachhea and thhe main
bronchi are
a shown in Figuree 2 and
Figure 3.. Both coontours aree almost
similar foor both heealthy and stenosis
models foor the restting flow rate (15
l/min). Thhere are no significant pressure
drop and velocity different
d
thrroughout
the tracheea and main bronchi for both
models. The
T
contouurs begin to
t show
different between both
b
modells when
simulated using 60 l//min and 100 l/min
flow rates.
From the Figure 2 (b)
( and Figuure 2 (c),
it shows that the presssure drop is
i higher
in the steenotic modeel especiallly at the
Healthy model
m
Stenosis model
m
47
(a) 15 l//min
(b) 60 l/m
min
Healthyy model
model
Healthy model
m
Stenosiis model
Sttenosis
(b) 60 l//min
(c) 100 l/m
min
Healthyy model
Steenosis
moddel
(c) 100 l/min
Healthy model
m
Stenosis model
m
Figure 2: Simulated pressure coontour in
the tracheea and mainn bronchi inn healthy
and stenoosis modelss at differeent flow
rates. (a) 15 l/min, (bb) 60 l/minn and (c)
100 l/min
Healthy mode
m
Stenosiss model
48
(a) 15 l/min
Figure 3: Simulated velocity contour in
the trachea and bronchus in healthy and
stenosis models at different flow rates.
(a) 15 l/min, (b) 60 l/min and (c) 100
l/min
B. Pressure and velocity distributions
Figure 4 and Figure 5 show the
simulated
pressure
and
velocity
distributions along the centerline of
healthy and stenosis models at different
flow rates.
In general, the pressure drop occur in
the stenosis model is much higher than
that in the healthy model. It is happens
due to the contraction at the stenosis
area that effect the pressure distribution
along the airways. The overall pattern
of the pressure distribution in stenosis
model still having the same pattern as
the healthy model except at the stenotic
area where the large drop of pressure
value take place. It is shown at every
flow rates applied for each model.
With reference to velocity distribution
plots, the pattern for both model
showing the same pattern except the
velocity in the stenosis model having
higher spped especially when reach the
stenosis area. For the resting flow rate
(15 l/min), there are not significant gap
between the healthy and stenosis model
and it started to have a different when
the flow rate increases.
Overall, due to the location of the
stenosis that located at the beginning of
the trachea which is far enough from the
bifurcation area, the pressure and the
velocity distribution did not effected the
flow characteristic too much and the
flow still reach at the main bronchi in
content condition.
(b) 60 l/min
(c) 100 l/min
Figure 4: CFD simulated pressure drop
along the centerline of trachea and main
bronchi in healthy and stenosis models
49
at different flow rates. (a) 15 l/min, (b)
60 l/min and (c) 100 l/min
(a) 15 l/min
Figure 5: CFD simulated velocity
distribution along the centerline of
trachea and main bronchi in healthy and
stenosis models at different flow rates.
(a) 15 l/min, (b) 60 l/min and (c) 100
l/min
Conclusion
Stenosis inside the trachea did affect the flow
characteristic for human airways. The results
show that the flow pattern will become more
non-uniform when the flow rates apply
increases. The results also show that the stenosis
affect the flow in the trachea as well as the inlet
flow condition into the main bronchi.
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