Secondary Velocity Fields in the Conducting Airways of the Human Lung

Fresconi, Frank; Prasad, Ajay K.

doi:10.1115/1.2768374

Cited by 50 publications

(46 citation statements)

References 31 publications

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“…This reduces the shear close to the inner side of the bifurcation. This is in contrast to the pattern found in the left main bronchus and in simplified geometries (Grosse et al 2007;Fresconi and Prasad 2007;Zhang and Kleinstreuer 2002).…”

Section: First Bifurcationcontrasting

confidence: 80%

“…However, these studies focus on limited regions of the bronchial tree, namely the first bifurcation. On the other hand, multiple studies (both numerical and experimental) indicate that, for moderate oscillation frequency, the effects of unsteadiness are minor (Zhang and Kleinstreuer 2002;Fresconi and Prasad 2007;Theunissen and Riethmuller 2008). Such a regime in which the viscous forces dominate the unsteady inertial forces is characterized by a Womersley number less than one:…”

Section: Introductionmentioning

confidence: 94%

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Three-dimensional inspiratory flow in the upper and central human airways

et al. 2015

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Section: First Bifurcationcontrasting

confidence: 80%

Section: Introductionmentioning

confidence: 94%

Three-dimensional inspiratory flow in the upper and central human airways

et al. 2015

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“…27,[31][32][33][34][35][36][37] In an oscillatory flow setting, a nonzero mean flow averaged over one time period may be observed. This nonzero mean flow can result in significant drift of particles at end cycle called steady streaming.…”

Section: B Eulerian Streaming Stokes Drift and Lagrangian Drift Vementioning

confidence: 99%

Steady streaming: A key mixing mechanism in low-Reynolds-number acinar flows

et al. 2011

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Study of mixing is important in understanding transport of submicron sized particles in the acinar region of the lung. In this article, we investigate transport in view of advective mixing utilizing Lagrangian particle tracking techniques: tracer advection, stretch rate and dispersion analysis. The phenomenon of steady streaming in an oscillatory flow is found to hold the key to the origin of kinematic mixing in the alveolus, the alveolar mouth and the alveolated duct. This mechanism provides the common route to folding of material lines and surfaces in any region of the acinar flow, and has no bearing on whether the geometry is expanding or if flow separates within the cavity or not. All analyses consistently indicate a significant decrease in mixing with decreasing Reynolds number ͑Re͒. For a given Re, dispersion is found to increase with degree of alveolation, indicating that geometry effects are important. These effects of Re and geometry can also be explained by the streaming mechanism. Based on flow conditions and resultant convective mixing measures, we conclude that significant convective mixing in the duct and within an alveolus could originate only in the first few generations of the acinar tree as a result of nonzero inertia, flow asymmetry, and large Keulegan-Carpenter ͑K C ͒ number.

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“…Confluent airstreams in the daughter bifurcations during exhalation produce secondary flows with two or more pairs of counter-rotating vortices. This complex pattern of secondary motion has an augmented dispersion effect that is similar to turbulence and results in relatively blunt cross-sectional velocity profiles in the trachea during exhalation (Fresconi and Prasad 2007;Longest and Vinchurkar 2009). Therefore, a uniform distribution of velocity at the laryngeal inlet appears to be a reasonable first order approximation to in vivo conditions.…”

Section: Boundary Conditionsmentioning

confidence: 98%

Characterization of Submicrometer Aerosol Deposition in Extrathoracic Airways during Nasal Exhalation

Longest

2009

Aerosol Science and Technology

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Submicrometer and especially fine aerosols that enter the respiratory tract are largely exhaled. However, the deposition of these aerosols under expiratory conditions is not well characterized. In this study, expiratory deposition patterns of both ultrafine (<100 nm) and fine (100-1000 nm) respiratory aerosols were numerically modeled in a realistic nasal-laryngeal airway geometry. Particle sizes ranging from 1 through 1000 nm and exhalation flow rates from 4 through 45 L/min were considered. Under these conditions, turbulence only appeared significant in the laryngeal and pharyngeal regions, whereas the nasal passages were primarily in the laminar regime. Exhaled particles were simulated with both a continuous-phase drift flux velocity correction (DF-VC) model and a discrete Lagrangian tracking approach. For the deposition of ultrafine particles, both models provided a good match to existing experimental values, and simulation results corroborated an existing in vivo-based diffusion parameter (i.e., D 0.5 Q −0.28 ). For fine particles, inertia-based deposition was found to have a greater dependence on the Reynolds number than on the Stokes number (i.e., St 0.1 k Re 0.9 ), indicating that secondary flows may significantly influence aerosol deposition in the nasal-laryngeal geometry. A new correlation was proposed for deposition in the extrathoracic airways that is applicable for both ultrafine and fine aerosols over a broad range of nasal exhalation conditions. Results of this study indicate that physical realism of the airway model is crucial in determining particle behavior and fate and that the laryngeal and pharyngeal regions should be retained in future studies of expiratory deposition in the nasal region.

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Secondary Velocity Fields in the Conducting Airways of the Human Lung

Cited by 50 publications

References 31 publications

Three-dimensional inspiratory flow in the upper and central human airways

Three-dimensional inspiratory flow in the upper and central human airways

Steady streaming: A key mixing mechanism in low-Reynolds-number acinar flows

Characterization of Submicrometer Aerosol Deposition in Extrathoracic Airways during Nasal Exhalation

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