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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, the dynamics of an orthonormal frame attached to each Lagrangian fluid particle undergoing three-axis rotations, by using quaternions in combination with Ertel's theorem for frozen-in vorticity, were derived.
Abstract: Experimentalists now measure intense rotations of Lagrangian particles in turbulent flows by tracking their trajectories and Lagrangian-average velocity gradients at high Reynolds numbers. This paper formulates the dynamics of an orthonormal frame attached to each Lagrangian fluid particle undergoing three-axis rotations, by using quaternions in combination with Ertel's theorem for frozen-in vorticity. The method is applicable to a wide range of Lagrangian flows including the three-dimensional Euler equations and its variants such as ideal magneto-hydrodynamics. The applicability of the quaterionic frame description to Lagrangian averaged velocity gradient dynamics is also demonstrated.

26 citations

Journal ArticleDOI
TL;DR: In this article, the topological and dynamical features of small scales are studied in the context of decaying magnetohydrodynamic turbulent flows using direct numerical simulations, showing that structures and dynamics at the time of maximum dissipation depend on the large scale initial conditions at the examined Reynolds numbers, and that each flow has a different shape for the joint probability density functions of the invariants of the velocity gradient in contrast to the universal teardrop shape of hydrodynamic turbulence.
Abstract: The topological and dynamical features of small scales are studied in the context of decaying magnetohydrodynamic turbulent flows using direct numerical simulations. Joint probability density functions (PDFs) of the invariants of gradient quantities related to the velocity and the magnetic fields demonstrate that structures and dynamics at the time of maximum dissipation depend on the large scale initial conditions at the examined Reynolds numbers. This is evident in particular from the fact that each flow has a different shape for the joint PDF of the invariants of the velocity gradient in contrast to the universal teardrop shape of hydrodynamic turbulence. The general picture that emerges from the analysis of the invariants is that regions of high vorticity are correlated with regions of high strain rate S also in contrast to hydrodynamic turbulent flows. Magnetic strain dominated regions are also well correlated with region of high current density j. Viscous dissipation (∝S2) as well as Ohmic dissipati...

25 citations

Journal ArticleDOI
TL;DR: The gas-kinetic BGK-NS scheme is extended to an adaptive grid for the viscous flow simulations, where the grid points can be easily moved and concentrated on the regions with large velocity and density gradients, such as the boundary layer and multi-material interface.

25 citations

Journal ArticleDOI
TL;DR: In this paper, the effects of geometrical and physical parameters such as Reynolds number, number of holes and nanoparticles volume fraction on the thermal and viscous entropy generation rates and Bejan number are investigated.
Abstract: Entropy generation analysis for the Cu–water nanofluid flow through a heat exchanger tube equipped with perforated conical rings is numerically investigated. Frictional and thermal entropy generation rates are defined as functions of velocity and temperature gradients. Governing equations are solved by using finite volume method, and Reynolds number is in the range of 5000–15,000. The effects of geometrical and physical parameters such as Reynolds number, number of holes and nanoparticles volume fraction on the thermal and viscous entropy generation rates and Bejan number are investigated. The results indicate that the thermal irreversibility is dominant in most part of the tube. But it decreases with increasing the nanoparticle volume fraction. Frictional entropy generation reduces with increasing the number of holes from 4 to 10. This is because of stronger velocity gradient near the perforated holes. Bejan number decreases with augment of Reynolds number.

25 citations

Journal ArticleDOI
TL;DR: In this article, the wall-adapting local eddy-viscosity (WALE) model was designed for large-eddy simulation (LES) of turbulent boundary layer, in transitional flow.

25 citations


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