Group Title: 7th International Conference on Multiphase Flow - ICMF 2010 Proceedings
Title: P1.21 - Study On the Unsteady Flow Field in an Idealized Human Mouth-Throat Model with Large Eddy Simulation
ALL VOLUMES CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00102023/00440
 Material Information
Title: P1.21 - Study On the Unsteady Flow Field in an Idealized Human Mouth-Throat Model with Large Eddy Simulation Particle-Laden Flows
Series Title: 7th International Conference on Multiphase Flow - ICMF 2010 Proceedings
Physical Description: Conference Papers
Creator: Cui, X.G.
Gutheil, E.
Publisher: International Conference on Multiphase Flow (ICMF)
Publication Date: June 4, 2010
 Subjects
Subject: circular idealized mouth-throat model
large eddy simulation (LES)
unsteady flow field
 Notes
Abstract: An idealized human mouth-throat model was constructed based on dimensions of a human cast (Cheng et al., 1999) in order to study the particle transport and deposition in the human upper respiratory system. The flow field in the upper airways was simulated using LES. For model validation, the time-averaged velocity at the centerline in a constricted tube is compared with experimental data (Ahmed et al., 1983) and numerical results from Reynolds-averaged Navier–Stokes (RANS) equations coupled with the LRN κ-ω model (Zhang et al., 2002). Moreover, the unsteady flow field is studied to understand the aerodynamic properties of the flow structure. The main properties of the flow field in the idealized geometry are presented and discussed in the present study. It is observed that the unsteady flow field is very different from the mean flow field after the soft palate. There are different length-scale secondary vortices distributed at different cross–sections along the axial direction in the separation zone, laryngeal jet zone, mixed zone, and the wall shear layer. In addition, the laryngeal jet is highly unsteady, in particular, at the location of laryngeal jet tail.
General Note: The International Conference on Multiphase Flow (ICMF) first was held in Tsukuba, Japan in 1991 and the second ICMF took place in Kyoto, Japan in 1995. During this conference, it was decided to establish an International Governing Board which oversees the major aspects of the conference and makes decisions about future conference locations. Due to the great importance of the field, it was furthermore decided to hold the conference every three years successively in Asia including Australia, Europe including Africa, Russia and the Near East and America. Hence, ICMF 1998 was held in Lyon, France, ICMF 2001 in New Orleans, USA, ICMF 2004 in Yokohama, Japan, and ICMF 2007 in Leipzig, Germany. ICMF-2010 is devoted to all aspects of Multiphase Flow. Researchers from all over the world gathered in order to introduce their recent advances in the field and thereby promote the exchange of new ideas, results and techniques. The conference is a key event in Multiphase Flow and supports the advancement of science in this very important field. The major research topics relevant for the conference are as follows: Bio-Fluid Dynamics; Boiling; Bubbly Flows; Cavitation; Colloidal and Suspension Dynamics; Collision, Agglomeration and Breakup; Computational Techniques for Multiphase Flows; Droplet Flows; Environmental and Geophysical Flows; Experimental Methods for Multiphase Flows; Fluidized and Circulating Fluidized Beds; Fluid Structure Interactions; Granular Media; Industrial Applications; Instabilities; Interfacial Flows; Micro and Nano-Scale Multiphase Flows; Microgravity in Two-Phase Flow; Multiphase Flows with Heat and Mass Transfer; Non-Newtonian Multiphase Flows; Particle-Laden Flows; Particle, Bubble and Drop Dynamics; Reactive Multiphase Flows
 Record Information
Bibliographic ID: UF00102023
Volume ID: VID00440
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: P121-Cui-ICMF2010.pdf

Full Text

7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


Study On the Unsteady Flow Field in an Idealized Human Mouth-Throat Model with Large
Eddy Simulation


X.G. Cui and E. Gutheil



Institutelnterdisziplinares Zentrum fur Wissenschaftliches Rechnen, Ruprecht-Karls-Universitat Heidelberg,
Im Neuenheimer Feld 368, 69120 Heidelberg, Germany
Xinguang.Cui@iwr.uni-heidelberg.de and gutheil@iwr.uni-heidelberg.de


Keywords: circular idealized mouth-throat model, large eddy simulation (LES), unsteady flow field




Abstract

An idealized human mouth-throat model was constructed based on dimensions of a human cast (Cheng et al., 1999) in order to
study the particle transport and deposition in the human upper respiratory system. The flow field in the upper airways was
simulated using LES. For model validation, the time-averaged velocity at the centerline in a constricted tube is compared with
experimental data (Ahmed et al., 1983) and numerical results from Reynolds-averaged Navier-Stokes (RANS) equations
coupled with the LRN K-) model (Zhang et al., 2002). Moreover, the unsteady flow field is studied to understand the
aerodynamic properties of the flow structure. The main properties of the flow field in the idealized geometry are presented and
discussed in the present study. It is observed that the unsteady flow field is very different from the mean flow field after the
soft palate. There are different length-scale secondary vortices distributed at different cross-sections along the axial direction
in the separation zone, laryngeal jet zone, mixed zone, and the wall shear layer. In addition, the laryngeal jet is highly
unsteady, in particular, at the location of laryngeal jet tail.


Introduction

Particle transport and deposition in the human respiratory
system has been studied intensely since the aerosol drugs
are used predominantly in the treatment of lung diseases
such as asthma and COPD (chronic obstructive pulmonary
disease). At present, most of the numerical simulations in
this area are carried out in one-coupled way (Zhang et al.,
2002; Matida et al., 2004; Jin et al., 2007; Jayaraju et al.,
2007), which means that the flow field is solved without
consideration of the particle motion; at the same time, the
flow field has great influence on the particle motion. To
understand the property of particle transport and deposition,
it is very important to better understand the properties of the
flow field.
It was shown that one of main flow characteristics in the
oral airway is flow transition from laminar to turbulent
(Zhang et al., 2002). Suitable RANS LRN K-) model
(Zhang et al., 2002) and LRN SST K-) model (Jayaraju et
al., 2007) for capturing the laminar-transitional-turbulent
flow were used in the computational fluid-particle dynamics
(CFPD) simulations in the respiratory system. Recently,
researchers have also implemented LES in the numerical
simulation of particle motion in the respiratory system. Jin
et al. (2007) used large eddy simulation to describe particle
transport in the human upper respiratory tract, and it
indicates the potential of LES to predict the aerosol particle
transport in this region. Jayaraju et al. (2008) compared LES
with the RANS SST K-) model, and they found that LES


predicts the flow field and particle deposition more correctly
than RANS methods since they were found to be closer to
experimental data. Ilie et al. (2008) applied LES for particle
transport in an idealized mouth-throat with a dry powder
inhaler mouth-piece inlet. They found that LES seems to
capture the flow structure that cannot be observed in the
RANS simulation, and moreover, it improves the prediction
of total particle deposition efficiency over the standard
RANS/EIM (eddy interaction method) approach.
Other features of the flow field were shown in the numerical
simulation of Zhang et al. 2(' I2). They include the
recirculation zone after the mouth cavity, the soft palate and
glottis, and the laryngeal jet. The flow structure can show
very different properties due to the different geometrical
topology. In the numerical results of Zhang et al.I ,2 I'2), no
turbulence is found at an inspiration flow rate of 15L/min,
but there is turbulence observed in the numerical simulation
of Jayaraju (2007) at the same flow rate. It was argued that
the geometry used by Zhang et al. ( 2 i 12 is simplified,
whereas Jayaraju et al. (2007) presented and discussed a
more realistic extrathroacic airway based on CT scans. It is
also interesting that the turbulence onset was observed in
the experimental study referenced by Staphen et al. (2000)
in the tracheal cast when the flow rate is more than 3L/min.
Due to glottal contribution, a laryngeal jet is generated after
the glottis in the trachea and the geometrical influence can
also be observed in the larynx. As emphasized by Xi et al.
(2008), the orientation between the larynx and the trachea
has great influence on the laryngeal jet within the trachea so






7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


that the laryngeal jet has different profiles. For instance, a
laryngeal jet located in the center of the trachea without
impinging on the wall is studied in the numerical simulation
of Zhang et al. (2i 112, They investigated a circular idealized
mouth-throat, which includes the circular larynx and straight
trachea (Zhang et al., 2002). However, several other studies
are in contrast to these findings. The studies of Jayaraju et
al. (2008) show the laryngeal jet to impinge on the front
side of the trachea in a simplified mouth-throat model with
forward-sloped larynx and straight trachea configuration. Xi
et al. (2008) found that the laryngeal jet is skewed towards
the right side of the trachea, they used an approximate
model of the upper tracheobronchial airways with a
forward-sloped larynx and rearward-sloped trachea. The
result is in agreement with the in vitro experiments of
Corcoran and Chigier (21 i 1,2 In addition, recently Lin et al.
(2007) found a laryngeal jet to approach the back of the
trachea in a patient-specific airway model with
rearward-sloped larynx and a straight trachea. In fact, not
only the orientation of the larynx and trachea influences the
entrance of the laryngeal jet, but also the shape of glottal
aperture affects the laryngeal jet and reverse flow pattern.
Brouns et al. (2007) studied the influence of the shape and
cross-section area on the flow structure with circular,
triangular, and elliptical glottal aperture in an idealized
mouth-throat model. It was found that the triangular glottal
aperture shifted the laryngeal jet in the direction of posterior
wall, and there were two pairs of counter-rotating secondary
vortices corresponding to one pair in the cases of circular
and elliptical apertures. In addition, the laryngeal jet also
influences the flow field in the tracheobronchial (TB)
region. Xi et al. (2008) found the secondary motion in the
daughter branches persistently to be stronger when computed
with the standard TB model compared to the laryngeal-TB
model. Moreover, a laryngeal jet is predicted using the
laryngeal-TB model. Lin et al. (2007) found that the
turbulence induced by the laryngeal jet can significantly
affect the flow patterns as well as tracheal wall stress, and
they also found, neglecting the oropharynx, that the larynx
generated different flow structures including velocity
parabola in the trachea, and turbulence was negligible.
In addition to concentrating on the laryngeal jet, researchers
recently started to pay more attention to other flow
structures in this region. Secondary flows in the form of
multi-vortex structures behavior in the context of double
bifurcation model were studied by Leong et al. (2009)
through numerical simulation and experimental
visualization. It was found that secondary vorticity is
amplified through the vortex line stretching due to the
secondary flow within the daughter tube. Ball et al. (2008)
used the RANS Kc-w model to conduct the high-resolution
turbulence modeling of airflow in an idealized human
extra-thoracic airway, and the flow structure was analyzed
through iso-surface plots of the negative second eigenvalue
(Jeong et al., 1995). It was observed that the recirculation
bubble formed anterior to the epiglottis. The laryngeal jet
impinging on the anterior wall of the trachea causes
circumferential flow resulting in repeating secondary
vortices. Lin et al. (2007) applied a proper orthogonal
decomposition (Holmes et al., 1996) technique to study the
vortices in an upper human airway based on
multidetector-row computed tomography scans. The
analysis reveals Taylor-Gortler-like (Lin et al., 2007; Saric,


soft palate


glottis


Figure 1. Three dimensional view of the circular idealized
mouth-throat geometry
1994) vortical structures to reside in the supraglottis and the
subglottis, and counter-rotating vortices appear in the
main-stem bronchi. Moreover, these vortical structures are
related to the regions of local maximum coherent
turbulence.
Even though, the laryngeal jet and secondary vortices have
been studied extensively as discussed above, few
investigations concern the time-dependent motion of the
flow structure.
The present paper concerns a numerical study of unsteady
flow characteristics in an idealized mouth-throat with LES.
The instantaneous flow field for different time steps is
analyzed. Properties of the secondary vortices and laryngeal
jet at instantaneous flow field are addressed.
The flow field will be used further for the numerical
simulation of particle motion.

Mouth-Throat Models

Two different geometries are used in the numerical
simulations. The first one is the axi-symmetric constricted
tube with a 75% area reduction, which is described by a
cosine function (Zhang et al., 2003) as:


R xz
r(z R 2 -cos -
T(Z)= 2 R
1R


for |zl D

for |z > D


The second configuration is an idealized mouth-throat
model shown in Fig. 1. More details about this
configuration are given by Cheng et al., 1999; Zhang and
Kleinstreuer, 2002; Kleinstreuer et al., 2003; and Cui and
Gutheil, 2010.


Governing Equations

Neglecting the influence of particles on the fluid and the
interaction between particles, a one-way coupling method is
adopted. For the flow field, three-dimensional (3-D)
incompressible Navier-Stokes (N-S) equations are used (Jin
et al., 2007). LES is used to treat the turbulence, and the
Smargorinsky sub-grid scale (SGS) model (Smargorinsky,





7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


1963) was adopted for small-scale turbulence.

If the volume-averaged variance (Jin et al., 2007) is described
as:
1 fx+1 Ax 2 fY+Yf+'z
O(x,y,z)= Ax- Ay- Az 2 A y (A ,p,t)ddidp

(2)

and after the filter processing of physical variables,
volume-averaged three dimension N-S equations (Jin et al.,
2007) can be given as:

9(pu.)
-a (3)
9x,
at axj I
p







(J the s d scale te

T i uu. (5)

with an eddy-viscosity assumption to model the SGS tensor
(Jin et al., 2007)


Numerical Method


The numerical solution includes the software platform
OpenFOAM 1.5 ijili'p .opencfd.co.uk/Openfoam/). A
new solver for the flow field with LES and the particle
motion with a Lagrangian tracking method was constructed
based on the solvers oodles and icolagrancianFoam
(www.openfoamwiki.net). In the present study, it is used to
simulate the flow field.
The computational grid was generated with Ansys
ICEM-CFD 11.0. An O-grid is used around the wall
surfaces, and a H-grid is adopted in the center of the
geometry. The mesh size is refined until the flow field is
independent of the number of grid nodes. The final number
of grid nodes is 2,771,226 for the constricted tube and
1,276,500 for the idealized mouth-throat model.
The velocity on the inlet surface is given as 0.473 m/s with
2% fluctuation, corresponding to Rem = 2,000 (Zhang et al.
2002). The steady inspiration flow rate with 30L/min
corresponding to normal breathing intensity with 2%
fluctuation is implemented. The static relative pressure at
the outlet is set to zero. No-slip boundary conditions are
used at the wall.
The computations are carried out at the bwGrid cluster at
Heidelberg University. The simulation takes around two
weeks using 56 processors for the flow field in the case of
an inspiration rate of 30 L/min.

Results and Discussion


-1
7 =2vS, +-T6



Sau+ au
'j 2 ax x


i, j = 1, 2, 3


v, =(Cs 2

where


S= S_,_ ,V2,


A = (Ax- Ay Az)3

The 3-D N-S equations can be rewritten as follows:

o(p, j )
-x
ax


9u, a ap]
at xj I x, P

+__ (v+v) --+ +T
ax [ ax ax,


Flow Field in the Constricted Tube
(6)
The flow field in the constricted tube transits from laminar
to turbulent and the geometry is rather simple, which
(7) qualifies this setting for evaluation of the present method.
The results are compared with experimental (Ahmed et al.,
1983) and numerical (Zhang et al., 2002) results. The
normalized axial velocities at the centerline are shown in
Fig. 2. The velocity is normalized by the mean velocity at
the inlet plane, Umean. The distance in the axial direction is
normalized by the tube diameter, D, and in the radial
5.0 0 Experimental data [1]
- - LRN K-Co [2]
(8) LES-Smargorinsky (present)
S. *


(10)
2.0 -



1.0 . .
0.0 2.0 4.0 6.0
zlD
(11) Figure 2. Comparison of the centerline velocity in a
constricted tube with experimental (Ahmed et al., 1983)
and numerical (Zhang et al., 2002) results.







7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


direction with the radius, R, of the tube. From experimental
data (Ahmed et al., 1983) it is known that the axial flow
velocity increases due to a reduced area, and it does not
change much until the location around Z = 2D. After this
relative steady period, the velocity deceases quickly because
of the flow transition from laminar to turbulent coupled with
large-scale lateral momentum transfer. In addition, it is
described that the flow transition occurs in the region from 1
< Z/D < 4. The comparison of the velocity at the centerline
is shown in Fig. 2. The present results fit well with both the
experimental (Ahmed et al., 1983) and numerical (Zhang et
al., 2002) results; in particular, in the transitional regime, it
performs better than the model of Zhang et al., 2002.
Comparison between the present result with both
experimental and numerical data are discussed in more
detail by Cui and Gutheil, 2010.
The comparison with different models and experiment
shows that the present methodology adequately predicts the
flow field transition from laminar to turbulent, and it
improves recent results of Zhang et al. (2'" I2 ).
In the following section, the second configuration will be
studied with the current LES/Smagorinsky formulation.



A U,, (cmis) A U(cmis)
1000 1000
o900 900
A00 A' 800
700 700
1.000 1600
B B' 600
500 B V 500
400 400
300 300
C C' 200 C c. 200
S100 100
D D' 0 D D" 0


E E' E K











(a) (b)

A u (cms) A U(cmls)
1000 1000
900 900
800 P 800
700 700
B 600 B600
500 B '500
400 400
300 300
C C' 200 C c. 200
100 1 100
D D' 0 D D' 0


E E' E E'










(c) (d)
Figure 3. Velocities at the mid-plane. (a): mean flow field.
(b) (d): instantaneous flow fields at times t = 0.4705s,
0.4710s, and 0.4715s, respectively.


A Umeanx (cms)

S270
240
210
80
120
90
30


(a) (b)

S U,(cm/s) A
S29
264
231
198
165
132
99
66
33
0


Ux (cm/s)
330
297
264
231
198
165
I 132
99
V6
33
) 1.






U, (cm/s)
S330
297
264
S198
185
132
99
1 66
33
o


(c) (d)
Figure 4. Axial velocities and secondary flow streamlines at
cross section A A' in the pharynx, (a): mean flow field and
(b) (d): instantaneous flow fields at t = 0.4705s, 0.4710s,
and 0.4715s, respectively.





Flow Field in the Idealized Mouth-Throat


In the remainder of the paper the properties of the unsteady
flow field in the mouth-throat, the time-averaged and
instantaneous velocity fields in the geometry shown in Fig.
3 are discussed. The velocity contour at the mid-plane of the
geometry is displayed. In particular, Fig. 3(a) shows the
mean flow field, and Figs. 3(b) (d) display unsteady
results at times t = 0.470s, 4710s, and 4715s, respectively.
Axial velocity contour plots and the secondary streamlines
at different cross sections along the axial direction are
U r,.n, (cm/s) U (cmls)


40 500
400 400
350 350
300 300
250 250

100 00
:o 50


U (cm/s)
S450
400
360
250
200
150 E
1 100
so
0


U (cmls)
S500
S450
400
350
300
250
200
150
100
50
0


(c) (d)
Figure 5. Axial velocities and secondary flow streamlines at
section B B' in the pharynx, (a): mean flow field. (b) (d):
instantaneous flow field at t = 0.4705s, 0.4710s, and
0.4715s, respectively.










shown in Figs. 4 8, which are corresponding to cross
section A A' in the mouth cavity, cross section B B' in
the pharynx, cross section C C' at the glottis, D D' cross
section at the one diameter of trachea downstream glottis,
and E E' cross section at three diameters of trachea
downstream the glottis. In these figures, the figure (a) shows
the averaged velocity profile and parts (b) (d) display
profiles at times t = 0.4705s, 4710s, and 4715s, respectively.
Positions A E denote the posterior side, and A' E' the
anterior side.
From Fig. 3 (a), it can be seen that the flow field captures
the main properties of the time-averaged flow field in the
idealized mouth-throat, including the skewed velocity
profile in the oral cavity and pharynx due to centrifugal
forces, and flow separation in the lower portion of the
mouth, in the pharynx region after the soft palate, and
downstream of the glottis. The asymmetric laryngeal jet
extends from the entrance of the glottis. There is a small
recirculation zone in the posterior side of pharynx and the
laryngeal jet is impinging on the anterior wall of the trachea.
In contrast to the numerical simulation of Zhang et al.,
2002, in a similar geometry, it is not impinging on the wall.
This is probably due to the different geometrical shape near
the soft palate and glottis. A very close look at Fig. 5(a)
reveals two pairs of counter-rotating secondary vortices with
different length scales at section B B' and one pair of
counter-rotating vortices at other cross-sections, see Figs.
4(a), Fig. 6(a), Fig. 7(a), Fig. 8(a).
From the velocity field at the mid-plane, it is observed that
the velocity field maintains almost the same profile in the
mouth cavity for both the mean and the instantaneous flow
fields at different times. At cross-section A A', it is seen
that the axial velocity profile remains steady and almost the
same as the averaged flow field. Moreover, there is minor
difference for the secondary streamlines between the mean
flow field and different time steps, although the big
secondary vortices profile is distorted at time t = 0.4715s.
These observations indicate that the flow field in the mouth
cavity is mainly laminar in this region.


meany(cm/s)
1000
I000
6700
600
500

200
1 0


Uy (cm/s)

C 700
600
500
400
300
200
100
1 0


U,(cmis)
1000
900
800
700
600
500
400
300
200
100
0*6


U, (cmls)
1000
700
600
500
S 400
300
200
100
0'


(c) (d)
Figure. 6 Axial velocities and secondary flow streamlines at
cross section C C' at glottis, (a): mean flow field. (b) (d):
instantaneous flow field at times t = 0.4705s, 0.4710s, and
0.4715s, respectively.


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


U mean (cmsS) U (cm/s)
S 1000 1000
800 800
700 700
600 : 00

200 200
100 100




(a) (b)
U, (cm/s) U, (cm/s)
S1000 1000
900 900
800 800









(c) (d)
Figure 7. Axial velocities and secondary flow streamlines at
600 600










cross section D D' at a distance of one trachea diameter
200 200
100 100




(c) (d)

Figure 7. Axial velocities and secondary flow streamlines at
cross section D D' at a distance of one trachea diameter
downstream the glottis, (a): mean flow field and (b) (d):
instantaneous flow at times t = 0.4705s, 0.4710s, and
0.4715s, respectively.
When the flow field enters into the pharynx, unsteadiness
occurs after the soft palate shown in Fig. 5 (b) at the
boundary of separation zone and main flow zone, and these
large-scale coherent flow structures at the boundary of
separation zone are unsteady, which is seen in Figs. 5 (b) -
(d). More details can be revealed from the secondary
streamlines at cross section B B'. A comparison of Fig.
5(a) and (b) shows the instantaneous flow field to be very
different with respect to the mean flow field. Both the axial
velocity profile and secondary flow are changing with time,
in particular, the velocity mixture pattern at the shear layer
between the main flow zone and the separation zone.
Compared with the average flow field, there are no
counter-rotating vortices observed in the instantaneous flow
field, and moreover, there are no counter-rotating secondary
vortices in flow field at any instant at sections other than A
- A'. However, there are large length-scale vortices in the
main flow zone, as shown in Figs. 5 (b) (d), near the
location of counter-rotating vortices in the mean flow field
displayed in Fig. 5 (a). Apart from these large-scale vortices
in the main flow zone, there are unsteady secondary vortices
at different length scales. They reside in the main flow
region, in the mixing zone, and in the separation region. The
motion of these unsteady coherent structures may increase
the mixing between the main flow region and the separation
region, and thus, they increase the turbulence intensity.
Moreover, the large length-scale vortices mainly appear in
the main flow zone and in the mixing zone as seen in Figs. 5
(b) (d).
When the flow enters the glottis, the laryngeal jet is
produced as can be seen in Fig. 3, section C C'. At this
section, c.f. Fig. 6, the laryngeal jet dominates, and the
geometry is constricted at the glottis causing the axial
velocity to increase. Although the axial velocity profile still
changes with time, the velocity is relatively uniform. A
comparison of the mean axial velocity profile shown in Fig.











Um.ny (cm/s)
630
540

E 4
S000
O3


(a) (b)
U (cm/s)
00a
810
720
630
540
450
2700
180
0
9^ 1 ^^P


U, (cm/s)
900
810
720
630
540
450
E 360
270
180






Uy (cm/s)
900
soo
S810
720
630
540
450
270
180
90


(c) (d)
Figure 8. Axial velocities and secondary flow streamlines at
cross section E E' at a distance of one trachea diameter
downstream the glottis, (a): mean flow field and (b) (d):
instantaneous flow at times t = 0.4705s, 0.4710s, and
0.4715s, respectively.
6 (a) with the instantaneous velocities, Figs. 6 (b) (d),
shows that the laryngeal jet profile is relatively steady in the
section. In contrast to the vortices in the B B' section, not
many large-scale vortices are observed in section C C'.
The vortices at the glottis tend to appear in the anterior side.
When the flow enters section D D' (Fig. 7), the laryngeal
jet still dominates the flow and a recirculation zone has
developed. The interaction between the separation zone and
the laryngeal jet causes high unsteadiness, which can be
seen in Figs. 3 (b) (d) and Figs. 7 (b) (d). Moreover, the
laryngeal jet itself is unsteady, c.f Figs. 7 (b) (d).
Unsteadiness increases the production probability of
secondary vortices in the flow field. Large-scale vortices are
observed in the shear layer of the laryngeal jet. Figures 7 (b)
- (d) show smaller scale vortices in the mid flow region, in
the reversed flow zone, and the wall shear layer of the
laryngeal jet, and in the separation zone.
When the flow enters into section E E' as shown in Figure
8, which is located at the tail of laryngeal jet (c.f. Fig. 3), the
separation zone has not directly touched the laryngeal jet,
and there is a gradient region between these zones. Figure 8
reveals that the laryngeal jet is highly unsteady, severely
deformed and split. At the same time, the separation zone in
the instantaneous flow field is considerably bigger
compared with the mean flow field, and it is highly
unsteady. The interface between the separation zone and the
laryngeal jet becomes concave. Moreover, vortices of
different length-scales reside in the separation zone, the
mixing zone, the laryngeal jet breakup location, and in the
wall shear layer. Large-scale secondary vortices mainly
appear in the separation zone. It is very interesting to find
that there are more relatively small vortices in this section,
particularly in the wall shear layer, since they may greatly
affect particle transport in this region.


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

Conclusions

The flow field in an idealized mouth-throat was simulated
and properties of the unsteady flow field were analyzed.
Particular attention was paid to secondary vortices
distribution and the laryngeal jet at instantaneous flow
fields. After the flow enters into the pharynx, it is found that
the instantaneous flow field greatly differs from the
time-averaged flow field with respect to the profile,
length-scale and distribution of secondary vortices, the
laryngeal jet profile, the recirculation zone, and the mixing
zone.
It is found that secondary vortices at very different length
scales exist in the flow field. There is minor difference
between the instantaneous and the time-averaged flow fields
in the mouth cavity, which means that the flow is mainly
laminar in this region. However, after the flow has entered
into the pharynx, it becomes unsteady and involves
turbulent structures. In contrast to the averaged flow field,
no counter-rotating vortices are seen in instantaneous flow
fields at the same location in the pharynx, but large-scale
secondary vortices exist in the main flow zone in the
pharynx. Behind the pharynx, no counter-rotating vortices
are observed in all instantaneous flow fields.
Depending upon the axial location and time, secondary
vortices occur in the separation zone, the mixing zone, the
main flow zone and the wall shear layer of the separation
zone and the laryngeal jet. Vortices appearing in the wall
shear layer have small scales, whereas those in the mixing
zone tend to be at larger scales. The laryngeal jet is highly
unsteady and it breaks up at the tail. The break up may help
the momentum redistribution and increase of the turbulence
intensity further downstream. The highly unsteady
recirculation zone resides at the posterior side downstream
the glottis, and it strongly affects the flow structure towards
the laryngeal jet. The mixing pattern changes with the
profile of the laryngeal jet, and its interface becomes
concave at the tail. It can be seen that the separation zone,
the laryngeal jet, and the secondary vortices are closely
interrelated.
Future research will focus on the inspiration flow rates of 15
L/min and of 60 L/min. Moreover, the effect of the complex
flow characteristics on particle transport (Cui and Gutheil,
2010) will be studied more extensively.

Acknowledgements

The authors gratefully acknowledge financial support of the
German Science Foundation (DFG) through International
Graduate College 710. They thank the Ministry for
Education and Research and the Ministry for Science,
Research and Arts Baden-Wuerttemberg for using bwGrid
at Heidelberg University.

References

Ahmed, S. A., Giddens, D. P. Velocity measurements in
steady flow through axisymmetric stenoses at moderate
Reynolds number. Journal of Biomechanics, 16: 505-516
(1983).









Ball, C. G., Uddin, M., and Pollard, A. High resolution
turbulence modelling of airflow in an idealised human
extrathoracic airway. Computers & Fluids, 37: 943-64
(2008).

Brouns, M., Verbanck, S., and Lacor, C. Influence of glottic
aperture on the tracheal flow. Journal of Biomechanics, 40:
165-72 (2007).

Corcoran, T. E., Chigier, N. Inertial deposition effects: a
study of aerosol mechanics in the trachea using laser
doppler velocity and fluorescent dye. Journal of
Biomechanical Engineering, 124: 629-637 (' I '2).

Cheng, Y. S., Zhou, Y., and Chen, B. T. Particle deposition
in a cast of human oral airways. Aerosol Science and
Technology, 31: 286-300 (1999).

Cui, X. G., Gutheil, E. Large eddy simulation of the
flow-field and micro-particle deposition in an idealized
mouth-throat. Proc. 23rd European Conference on Liquid
Atomization and Spray Systems, Brno, Czech Republic
(2010).

Holmes, P., Lumley, J. L., and Berkooz, G. Turbulence,
coherent structures, dynamical systems and symmetry.
Cambridge University Press (1996).

Ilie, M., Matida, E. A., and Finlay, W. H. Asymmetrical
aerosol deposition in an idealized mouth with a DPI
mouthpiece inlet. Aerosol Science and Technology, 42(1):
10-17 (2008).

Jayaraju, S.T., Brouns, M., Verbanck, and S., Lacor, C.
Fluid flow and particle deposition analysis in a realistic
extrathoracic airway model using unstructured grids.
Journal ofAerosol Science, 38: 494-508 (2007).

Kleinstreuer, C., Zhang, Z. Laminar-to-turbulent
fluid-particle flows in a human airway model. International
Journal ofMultiphase Flow, 29: 271-289 ,:,' i1).

Jayaraju, S.T., Brouns, M., Lacor, C., Belkassem, B., and
Verbanck, S. Large eddy and detached eddy simulations of
fluid flow and particle deposition in a human mouth-throat.
Journal ofAerosol Science, 39(10): 862-875 (2008).

Jeong, J., Hussain, F. On the identification of a vortex.
Journal ofFluid Mechanics, 285: 69-94 (1995).

Jin, H. H., Fan, J. R., Zeng, M. J., and Cen, K. F. Large
eddy simulation of inhaled particle deposition within the
human upper respiratory tract. Journal of Aerosol Science,
19: 257-268 (2007).

Leong, F. Y., Smith, K. A., and Wang, C. H. Secondary
flow behavior in a double bifurcation. Physics of Fluids, 21:
043601 (2009).

Lin, C. L., Tawhai M. H., McLennan, G., and Hoffman, E.
A. Characteristics of the turbulent laryngeal jet and its effect
on airflow in the human intra-thoracic airways. Respiratory
Physiology & Neurobiology, 157: 295-309 (2007).


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

Matida, E. A., Finlay, W. H., Lange, C. F., and Grgic, B.
Improved numerical simulation of aerosol deposition in an
idealized mouth-throat. Journal ofAerosol Science, 35: 1-19
(2004).

Saric, W.C. Gortler vortices. Annual Review of Fluid
Mechanics, 26: 379-409 (1994).

Smagorinsky, J. General circulation experiments with the
primitive equation. Monthly Weather Review, 91: 99-164
(1963).

Stapleton, K. W., Guentsch, E., Hoskinson, M. K., and
Finlay, W. H. On the suitability of Kc- turbulence modelling
for aerosol deposition in the mouth and throat: a comparison
with experiment. Journal of Aerosol Science, 31: 739-749
(2000).

Xi, J. X., Longest, P. W., and Martonen T. B. Effects of
the laryngeal jet on nano- and microparticle transport and
deposition in an approximate model of the upper
tracheobronchial airways. Journal of Applied physiology,
104: 1761-77 (2008).

Zhang, Z., Kleinstreuer, C., and Kim, C. S. Micro-particle
transport and deposition in a human oral airway model.
Journal ofAerosol Science, 33(12): 1635-1652 (21 "' ).

Zhang, Z., Kleinstreuer, C. Low-reynolds-number turbulent
flows in locally constricted conduits: a comparison study.
American Institute ofAeronautics and Astronautics Journal
(AIAA J) 41: 831-840 (2'1 11).




University of Florida Home Page
© 2004 - 2010 University of Florida George A. Smathers Libraries.
All rights reserved.

Acceptable Use, Copyright, and Disclaimer Statement
Last updated October 10, 2010 - Version 2.9.7 - mvs