Three-dimensional Voronoï analysis is performed to quantify both global and local aspects of clustering of inertial spheroidal particles in wall turbulence using data sets from a direct numerical simulation coupled with a Lagrangian point-particle approach. We consider oblate and prolate spheroids and characterize their inertia and shape by means of the Stokes number St and aspect ratio λ, respectively. It is observed that particles tend to drift toward the wall, and this tendency is most prominent for St = 30. Although inertia dominates over shape on the particle clustering, intermediate asphericity (λ = 0.33 and 3) is found to promote spheroids’ flux to the wall for St ≤ 30, while heavy spheroids (St = 100) with greater departure from spheres (λ = 0.1 and 10) distribute more evenly across the channel. The tendency of inertial spheroids to concentrate locally in preferred turbulence structures decreases with the distance from the walls. Owing to the particles’ preferential distribution in lower-than-mean fluid velocity regions, the local clustering of spheroidal particles decreases with the increasing asphericity. Particles with large inertia (St ≥ 30), especially spheres and prolate spheroids, are more likely to cluster in the viscous sublayer.

The dynamical behavior of inertial disk-like particles in turbulent vertical channel flow is investigated by an Eulerian-Lagrangian point-particle approach. Gravity effects on distribution, translation, rotation and orientation statistics of non-spherical particles modeled as oblate spheroids have been studied both in an upward and a downward flow and compared with results obtained in the absence of gravity. Altogether 12 different particle classes have been studied, with inertia and shape parameterized by means of Stokes number St and aspect ratio λ ≤ 1. The St =5 disk-like particles distribute more evenly across the channel in upward than in downward flow.The gravity effect on the particle concentration diminishes with large inertia and the spheroid shape has only a modest influence. Although the gravity significantly affects the streamwise and wall-normal mean slip velocities with increasing inertia, the particle shape rarely has any impact on the translational motion, except for the mean wall-normal velocity. The fluctuations of the velocity of disk-like particles are mainly ascribed to inertia, whereas the gravity and shape only have marginal effects. The presence of gravity is moreover found to have a negligible effect on the particles' orientation and rotation, in spite of the striking effect of λ on the orientation and rotation seen in the near-wall region. The tendency of the disks to align their symmetry axis orthogonal to the fluid vorticity in the channel center is stronger for particles with modest inertia.In the near-wall region, however, oblate spheroids preferentially align with the fluid vorticity for St >>1. The observed behavior is believed to be caused by the influence of the gravity force on the turbophoresis; i.e. that inertial particles move towards low-turbulence regions.

The effect of maxillary skeletal expansion (MSE) on upper airway in adolescent patients is not clear. The purpose of this study was to determine the upper airway airflow with MSE treatment using computational fluid dynamics analysis. Three-dimensional upper airway finite element models fabricated from cone beam computed tomography images were obtained before and after treatment in an adolescent patient with maxillary constriction. Turbulent analyses were applied. The nasal cavity (NC) was divided into 6 planes along the y-axis and the pharynx was divided into 7 planes in the z-axis. Changes in cross-sectional area, airflow velocity, pressure, and total resistance at maximum expiration and maximum inspiration were determined at each plane after MSE treatment. The greatest increase in area occurred in the oropharynx which was around 40.65%. The average increase in area was 7.42% in the NC and 22.04% in the pharynx. The middle part of pharynx showed the greatest increase of 212.81 mm2 and 217.99 mm2 or 36.58% and 40.66%, respectively. During both inspiration and expiration, airflow pressure decreased in both the NC and pharynx, which ranged from −11.34% to −23.68%. In the NC, the average velocity decrease was -0.18 m/s at maximum expiration (ME) and −0.13 m/s at maximum inspiration (MI). In the pharynx, the average velocity decrease was -0.07 m/s for both ME and MI. These results suggest that treatment of maxillary constriction using MSE appliance may show positive effects in improvement of upper airway cross-sectional areas and reduction of upper airway resistance and velocity.

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