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Velocity gradient

About: Velocity gradient is a research topic. Over the lifetime, 3013 publications have been published within this topic receiving 77120 citations.


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TL;DR: In this paper, non-axisymmetric density features, so called clumps, form primarily at the base of the wind on super-Sobolev length scales, and the density of clumps differs by a factor of 3$ from the azimuthal average, the magnitude of their velocity dispersion is comparable to the flow velocity and they produce $\sim 20\%$ variations in the column density.
Abstract: We study non-axisymetric features of 3D line driven winds in the Sobolev approximation, where the optical depth is calculated using the full velocity gradient. We find that non-axisymmetric density features, so called clumps, form primarily at the base of the wind on super-Sobolev length scales. The density of clumps differs by a factor of $\sim 3$ from the azimuthal average, the magnitude of their velocity dispersion is comparable to the flow velocity and they produce $\sim 20\%$ variations in the column density. Clumps may be observable because differences in density produce enhancements in emission and absorption profiles or through their velocity dispersion which enhances line broadening.

20 citations

Journal ArticleDOI
TL;DR: An orthokinetic coagulation model including the effects of agglomeration and local stress-induced aggregate breakup was developed and it was concluded that mass transfer between regions of varying flow strain rate and/or velocity gradient should be included in accurate coagulations modeling.

19 citations

Journal ArticleDOI
TL;DR: In this article, the authors studied the migration of chiral particles in shear flow by parallel disk rotational rheometer and showed that the particles can be separated by the velocity gradient field.
Abstract: The migration of chiral particles in shear flow is studied by parallel disk rotational rheometer. The chiral particles, made of silicon rubber with its two edges cut, are placed between the disks. When the disk rotates, the chiral particles move not only along the flow direction, but also migrate along the direction perpendicular to the flow (i.e., the radial direction). The migration direction, inner or outer, is determined by the handedness of the particle. This is the first experiment to show that the chiral particles can be separated by the velocity gradient field. The migration velocity is measured as a function of the shear rate, and compared with the result of simulation.

19 citations

Journal ArticleDOI
TL;DR: In this paper, a finite element analysis of the velocity profile for 30, 50, and 80% stenoses provides a basis for the study of the experimental results, and the authors show that in the presence of 30 and 50% stenosis, particularly for the low velocities which would be associated with diastole, the duration of the signal correlation increases in a region which is distal to the stenosis and near the vessel walls.
Abstract: A theoretical and experimental study of the received ultrasonic signal from calibrated stenotic flow phantoms is presented. A finite element analysis of the velocity profile for 30, 50, and 80% stenoses provides a basis for the study of the experimental results. High-resolution images of the returned signal obtained from a unique experimental system and a high volume concentration of scatterers are then presented. The authors show that in the presence of 30 and 50% stenoses, particularly for the low velocities which would be associated with diastole, the duration of the signal correlation increases in a region which is distal to the stenosis and near the vessel walls, rather than the expected decrease. This results from the decrease in the mean velocity and velocity spread within this region. In the presence of high velocities associated with systolic flow, the magnitude of the reverse flow component increases as does the peak velocity in the center of the vessel. These changes produce an increase in the radial velocity gradient, a shift in the gradient peak, and a decrease in the correlated signal interval in comparison with laminar flow. Thus, the spatial variation in the mean velocity and velocity gradient, and spatial variation in the signal correlation can be used to detect the change in the flow profile. >

19 citations

Journal ArticleDOI
TL;DR: The flow structure of one isothermal swirling case in the Sydney swirl flame database was studied using two numerical methods: Reynolds-averaged Navier-Stokes (RANS) approach and large eddy simulation (LES) as mentioned in this paper.
Abstract: The flow structure of one isothermal swirling case in the Sydney swirl flame database was studied using two numerical methods. Results from the Reynolds-averaged Navier-Stokes (RANS) approach and large eddy simulation (LES) were compared with experimental measurements. The simulations were applied in two different Cartesian grids which were investigated by a grid independence study for RANS and a post-estimator for LES. The RNG k-ɛ turbulence model was used in RANS and dynamic Smagorinsky-Lilly model was used as the sub-grid scale model in LES. A validation study and cross comparison of ensemble average and root mean square (RMS) results showed LES outperforms RANS statistic results. Flow field results indicated that both approaches could capture dominant flow structures, like vortex breakdown (VB), and precessing vortex core (PVC). Streamlines indicate that the formation mechanisms of VB deducted from the two methods were different. The vorticity field was also studied using a velocity gradient based method. This research gained in-depth understanding of isothermal swirling flow.

19 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202318
202233
2021127
2020116
2019134
201892