Computational flow modeling
of the equine upper airway
Introduction
Objectives
 Development of a computational turbulence model
for modeling flow through the equine airway
• Prediction of the minimum larynx size required
for normal airflow
• Determination of flow and pressure
characteristics on the soft palate
• Basis for investigation of new management/
therapeutic approaches for many ailments
affecting the equine respiratory system
Modeling: Schematic of the Steps
CT Scan
3D Reconstruction
Mimics®
Geometry Manipulation
Magics®
Change
Abduction
Surface Mesh
Magics®
Volume Mesh
TGrid®
Solve Flow Equations
Fluent®
Geometry Acquisition – CATSCAN
 Picker PQS CT scanner
 Slice thickness: 5 mm, Table index: 5 mm
3D Reconstruction
 Mimics
 Nasal cavity, Sinuses, Nasopharynx, Pharynx, Larynx and
Cranial trachea
 Export Format: STL, Triangle defined 3D Geometry
Geometry Manipulation
 Magics
• Removal of
Unwanted
parts
• Smoothing
• Creation of
inflow and
outflow
surfaces
Surface Mesh
 Magics
• Mesh Refinement
to improve Mesh
Quality
• Skewness should
be less than 0.85
for subsequent
interior mesh
generation and
numerical
analysis
Volume Mesh
 TGrid
Schematic
Solve Flow Equations
Governing Equations
Reynolds Averaged Navier-Stokes Equation:
Boussinesq Approximation:
Standard k-e Model
Boundary Conditions
• Atmospheric
pressure at inlet
• Outlet Pressures (30
cm from the larynx)
shown in the Figure
• Reynolds Number ~
80000
• Turbulence intensity
• Inlet: 1%
• Outlet: 5%
• Hydraulic Diameter
• Inlet: 0.057
• Outlet: 0.071
Fig. Tracheal Pressures in exercised horses
( Nielan, Rehder, Ducharme, & Hackett, 1992)
Results
Model Validation
Table 1:
Comparison of
modeled and
measured flows
Inspiratory Peak
Flow Rate (L/s)
Expiratory Peak
Flow Rate (L/s)
Model Computed
Values
65.2
31.2
Experimental Values
(Nielan et al, 1992)
65.5
84.0
Model Validation (contd..)
40
20
flow (L/s)
0
0
0.2
0.4
0.6
0.8
1
1.2
-20
-40
-60
-80
time (s)
Figure : Volume flow across the
tracheal outlet (L/s). Inspiratory
flows are negative, expiratory are
positive.
Figure : Flow trace of a galloping horse.
The corresponding pressure trace for
this horse has two-fold higher exhalation
pressures than those used for the model.
Flow Profile
Flow Profile- Discussion
 Flow velocities are higher at the bottom of the nasal
passage.
 Eddies are formed in the sinuses
Flow across the Larynx




Average Flow Velocity = 26.9 m/s
Pressure = -4300 Pa
Reynolds Number = 63000
Velocities are mostly uniform across the larynx.
The velocity near the walls are lower as expected.
Velocity
Velocities across the nostril (inlet2) larynx, and outlet
20
velocity (m/s)
10
0
-10
0
0.2
0.4
0.6
0.8
1
velocity magnitude on
inlet2
-20
velocity magnitude on
larynx
-30
velocity magnitude on
outlet
-40
-50
time(s)
Figure 10: Computed average velocities at different cross sections in
the nasal cavity
Summary


Limitations
• Enhancement in the model by changing the geometry to
improve prediction in the exhalation phase of breathing
Future Work
• Incorporate Temperature and Moisture Transport
• Analysis for different degree of abduction of the larynx
50% Abduction of the larynx
75% Abduction