Topic
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 article, the authors used a laser gradient meter to measure the wall velocity gradient with high spatial resolution and found that the measurement of the mean velocity gradient is less influenced by the nonlinearity of the velocity profile more distant from the wall than are the turbulence statistics.
52 citations
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TL;DR: In this paper, the role of structure in velocity gradient tensor statistics is examined for all local (incompressible) flow topologies characterisable by turbulent structures through the footprints they leave in conditional averages of the field, pertinent to non-local strain production.
Abstract: The statistics of the velocity gradient tensor , which embody the fine scales of turbulence, are influenced by turbulent ‘structure’. Whilst velocity gradient statistics and dynamics have been well characterised, the connection between structure and dynamics has largely focused on rotation-dominated flow and relied upon data from numerical simulation alone. Using numerical and spatially resolved experimental datasets of homogeneous turbulence, the role of structure is examined for all local (incompressible) flow topologies characterisable by . Structures are studied through the footprints they leave in conditional averages of the field, pertinent to non-local strain production, obtained using two complementary conditional averaging techniques. The first, stochastic estimation, approximates the field conditioned upon and educes quantitatively similar structure in both datasets, dissimilar to that of random Gaussian velocity fields. Moreover, it strongly resembles a promising model for velocity gradient dynamics recently proposed by Wilczek & Meneveau (J. Fluid Mech., vol. 756, 2014, pp. 191–225), but is derived under a less restrictive premise, with explicitly determined closure coefficients. The second technique examines true conditional averages of the field, which is used to validate the stochastic estimation and provide insights towards the model’s refinement. Jointly, these approaches confirm that vortex tubes are the predominant feature of rotation-dominated regions and additionally show that shear layer structures are active in strain-dominated regions. In both cases, kinematic features of these structures explain alignment statistics of the pressure Hessian eigenvectors and why local and non-local strain production act in opposition to each other.
52 citations
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TL;DR: In this paper, the authors used two ASCA observations of the Centaurus cluster to produce a velocity map for the gas in the cluster's central regions and found a significant (>99.8% confidence level) velocity gradient along a line near-perpendicular to the direction of the incoming subgroup and with a maximum velocity difference of ~3.4+-1.1 x 10−3.
Abstract: Several recent numerical simulations of off-center cluster mergers predict that significant angular momentum with associated velocities of a few x 10^{3} km/s can be imparted to the resulting cluster. Such gas bulk velocities can be detected by the Doppler shift of X-ray spectral lines with ASCA spectrometers. Using two ASCA observations of the Centaurus cluster, we produced a velocity map for the gas in the cluster's central regions. We also detected radial and azimuthal gradients in temperature and metal abundance distributions, which seem to be associated with the infalling sub-group centered at NGC 4709 (Cen 45). More importantly, we found a significant (>99.8% confidence level) velocity gradient along a line near-perpendicular to the direction of the incoming sub-group and with a maximum velocity difference of ~3.4+-1.1 x 10^{3} km/s. It is unlikely (P < 0.002) that the observed velocity gradient is generated by gain fluctuations across the detectors. While the observed azimuthal temperature and abundance variations can be attributed to the interaction with Cen 45, we argue that the intracluster gas velocity gradient is more likely due to a previous off-center merging event in the main body of the Centaurus cluster.
51 citations
01 Jul 1955
TL;DR: In this paper, the authors presented relations for the calculation of heat transfer at the forward stagnation point of both two-dimensional and axially symmetric blunt bodies, which were obtained from exact solutions to the equations of the laminar boundary layer, are presented in terms of local velocity gradient at the stagnation point.
Abstract: Report presenting relations for the calculation of heat transfer at the forward stagnation point of both two-dimensional and axially symmetric blunt bodies. The relations for the heat transfer, which were obtained from exact solutions to the equations of the laminar boundary layer, are presented in terms of local velocity gradient at the stagnation point.
51 citations
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TL;DR: In this paper, the authors present the first experimental evidence of a colloidal motor behavior of a suspension, which is obtained by making use of Quincke rotation: the spontaneous rotation of insulating particles suspended in a weakly conducting liquid when the system is submitted to a DC electric field.
51 citations