1. Computational flow modeling of the equine upper airway

2. Introduction

3. 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

4. Modeling: Schematic of the Steps
CT Scan
3D Reconstruction
Mimics®
Geometry Manipulation
Magics®
Surface Mesh
Magics®
Change
Abduction
Volume Mesh
TGrid®
Solve Flow Equations
Fluent®

5. Geometry Acquisition – CATSCAN
Picker PQS CT scanner
Slice thickness: 5 mm, Table index: 5 mm

6. 3D Reconstruction Mimics
Nasal cavity, Sinuses, Nasopharynx, Pharynx, Larynx and Cranial trachea
Export Format: STL, Triangle defined 3D Geometry

7. Geometry Manipulation
Magics
Removal of Unwanted parts
Smoothing
Creation of inflow and outflow surfaces

8. Surface Mesh Magics Mesh Refinement to improve Mesh Quality
Skewness should be less than for subsequent interior mesh generation and numerical analysis

9. Volume Mesh
TGrid

10. Schematic

11. Solve Flow Equations

12. Governing Equations Reynolds Averaged Navier-Stokes Equation:
Boussinesq Approximation:

13. Standard k-e Model

14. 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)

15. Results

16. 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

17. Model Validation (contd..)
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.

18. Flow Profile

19. Flow Profile- Discussion
Flow velocities are higher at the bottom of the nasal passage.
Eddies are formed in the sinuses

20. Flow across the Larynx Average Flow Velocity = 26.9 m/s
Pressure = Pa
Reynolds Number = 63000
Velocities are mostly uniform across the larynx. The velocity near the walls are lower as expected.

21. Velocity
Figure 10: Computed average velocities at different cross sections in the nasal cavity

22. 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