<p>An accurate understanding
of the respiratory fluid dynamics is instrumental for medical applications, such
as drug delivery system and treatment of diseases. Substantial research has
been done to study such flow. However, a great number of these studies have the
prevailing assumption of having a smooth wall, in despite the human trachea and
bronchi is sustain by a series of cartilaginous rings, which creates height
differences near the wall. To study the effect of including cartilaginous rings
in the respiratory flow we developed two experiments, presenting a comparison
between a smooth model and a model with cartilaginous rings. First, we present
an experimental observation of a simplified Weibel-based model of the human
trachea and bronchi with cartilaginous rings. The experiments were carried out
with a flow rate comparable with a resting state (trachea-based Reynolds number
of Re<sub>D</sub> = 2650). In the second experiment, we developed a similar
experiment but in a model with a tracheal stenosis (70% in the middle of the model) and no bronchi. In
this case we increase the Reynolds number to Re<sub>D </sub>= 3350, still a
resting breathing state condition.</p>
<p>For both experiments, we
used transparent models and refractive index-matching methods were used to
observe the flow, particularly near the wall. The flow was seeded with tracers
to perform particle image velocimetry and particle tracking velocimetry to
quantify the effect the rings have on the flow near the trachea and bronchi
walls. From the results, we present a previously unknown phenomenon in the
cavities between the cartilaginous rings: a small recirculation is observed in
the upstream side of the cavities throughout the trachea. This recirculation is
due to the adverse pressure gradient created by the expansion, which traps particles
within the ring cavity. In addition, we found that the cartilaginous rings induce velocity fluctuations into the
flow, which enhances the near-wall momentum of the flow reducing the separation
after the stenosis. Size of the recirculation is reduced by 11% and the maximum
upstream velocity is reduced by 38%, resulting in a much weaker recirculation
because of the rings. Also noticed a delay in the separation from the trachea
to bronchi bifurcation. </p>
<p>The detection of recirculation zones in the cartilage ring
cavities and the perturbation sheds light on the particle deposition mechanism
and helps explain results from previous studies that have observed an
enhancement of particle deposition in models with cartilage rings. The results
highlight the importance to include the cartilaginous rings in respiratory flow
studies. Finally, we compared the results from the stenotic case with Reynolds-averaged
Navier-Stokes (RANS) models (k
– ε, k – ε RNG, k – ω, k – ω SST, k – ω SST LRN and 4-equation Transition SST).
In the results, indicate significant
discrepancies between the experimental measurements and the simulations, mainly
in the area with flow separation after the contraction. Therefore, RANS
algorithms should not be considered reliable for research purposes in
respiratory fluid dynamics without experimental validation. </p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/8980244 |
| Date | 15 August 2019 |
| Creators | Jose Alberto Montoya Segnini (7023242) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/Experimental_Analysis_of_the_Effect_of_Cartilaginous_Rings_in_Tracheobronchial_Flow_and_Stenotic_Trachea_Flow/8980244 |
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