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Freestream

About: Freestream is a research topic. Over the lifetime, 3428 publications have been published within this topic receiving 56147 citations.


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Journal ArticleDOI
TL;DR: Computational fluid dynamics was used to investigate particle aspiration efficiency in low-moving air typical of occupational settings, and orientation-averaged simulation estimates of aspiration efficiency agree with the linear form of the proposed linear low-velocity inhalable convention through 100 µm.
Abstract: Computational fluid dynamics was used to investigate particle aspiration efficiency in low-moving air typical of occupational settings (0.1-0.4 m s(-1)). Fluid flow surrounding an inhaling humanoid form and particle trajectories traveling into the mouth were simulated for seven discrete orientations relative to the oncoming wind (0°, 15°, 30°, 60°, 90°, 135° and 180°). Three continuous inhalation velocities (1.81, 4.33, and 12.11 m s(-1)), representing the mean inhalation velocity associated with sinusoidal at-rest, moderate, and heavy breathing (7.5, 20.8, and 50.3 l min(-1), respectively) were simulated. These simulations identified a decrease in aspiration efficiency below the inhalable particulate mass (IPM) criterion of 0.5 for large particles, with no aspiration of particles 100 µm and larger for at-rest breathing and no aspiration of particles 116 µm for moderate breathing, over all freestream velocities and orientations relative to the wind. For particles smaller than 100 µm, orientation-averaged aspiration efficiency exceeded the IPM criterion, with increased aspiration efficiency as freestream velocity decreased. Variability in aspiration efficiencies between velocities was low for small (<22 µm) particles, but increased with increasing particle size over the range of conditions studied. Orientation-averaged simulation estimates of aspiration efficiency agree with the linear form of the proposed linear low-velocity inhalable convention through 100 µm, based on laboratory studies using human mannequins.

23 citations

Journal ArticleDOI
TL;DR: In this article, the effects of building generated turbulent winds on the flight performance of autonomous quadrotors are modeled using time accurate Large Eddy Simulations where five representative points within the building wake are used to predict an average position hold deviation.

23 citations

01 Jan 1987
TL;DR: In this paper, the turbulent boundary layer under a freestream velocity that varies sinusoidally in time around a zero mean is considered, and a theory for the velocity and stress profiles at high Reynolds number is formulated.
Abstract: The turbulent boundary layer under a freestream velocity that varies sinusoidally in time around a zero mean is considered. The flow has a rich variety of behaviors including strong pressure gradients, inflection points in the velocity profile, and reversal of the shear stress. A theory for the velocity- and stress profiles at high Reynolds number is formulated. Well-resolved direct Navier-Stokes simulations are conducted over a narrow range of Reynolds numbers. The flow is also computed over a wider range of Reynolds numbers using a new algebraic turbulence model. The results produced by the three approaches and by experiments are compared. Detailed phase-averaged statistical results from the direct simulations are provided to assist turbulence-model development.

23 citations

Proceedings ArticleDOI
13 Jan 2014
TL;DR: In this article, a grid resolution study is presented in which the resolution required to resolve the flow within the cavity is determined and the effects of wall temperature and the thickness of the oncoming turbulent boundary on the solutions are examined and found not to affect the mean velocity and turbulence, and to affect mean mixing only slightly.
Abstract: Simulation results are presented for non-reacting flow within a supersonic cavity flameholder. The freestream is air at Mach 2. A case is simulated with no fuel injection, and two cases are simulated with different rates of ethylene fuel injected through holes located on the back face of the cavity. The simulations correspond to a series of experiments for which particle image velocimetry measurements of two velocity components were made within the cavity. The flow within the cavity is computed using unsteady hybrid Reynolds-averaged Navier-Stokes/large-eddy simulation, as well as steady-state Reynolds-averaged NavierStokes simulations. A thorough grid resolution study is presented in which the resolution required to resolve the flow within the cavity is determined. The effects of wall temperature and the thickness of the oncoming turbulent boundary on the solutions is examined and found not to affect the mean velocity and turbulence, and to affect mean mixing only slightly. For steady-state Reynolds-Averaged Navier-Stokes simulations, several turbulence models are used and compared to the hybrid Reynolds-averaged Navier-Stokes/large-eddy simulation results, and the effects of the turbulent Schmidt number, are investigated. The influence of the side walls are investigated by comparing simulations of the full-width duct to simulations of a partial-width duct that uses periodic boundary conditions. The results of the simulations are also compared to the velocity measurements from the experiments, and the hybrid Reynolds-averaged Navier-Stokes/large-eddy simulation results are found to compare well with the experiment in most locations.

23 citations

Journal ArticleDOI
TL;DR: In this article, the diffusion of a thin tangential jet of an aqueous solution of drag-reducing polymer injected into the water- turbulent boundary layer of a flat plate at a freestream Reynolds number, 3.6 x 10 to the seventh power, and the accompanying drag reduction are investigated for a variety of initial concentrations and ratios of injection to freestrain velocities.
Abstract: The diffusion of a thin tangential jet of an aqueous solution of drag-reducing polymer injected into the water- turbulent boundary layer of a flat plate at a freestream Reynolds number, 3.6 x 10 to the seventh power, and the accompanying drag reduction are investigated for a variety of initial concentrations and ratios of injection to freestream velocities. The concentration distribution along the wall is found to be mainly represented by two regions. In the first region the wall concentration is practically constant and equal to the injected one; in the second region the concentration varies approximately as the inverse of the distance from the injection slit. The length of the first region is significantly increased by the polymer solution injection as compared with the pure solvent injection. The drag-reduction effect associated with the polymer injection depends on the trailing-edge concentration achieved as a result of the diffusion process.

23 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023195
2022350
2021108
2020113
201986
2018118