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1.
In the transitional channel flow, the large-scale intermittent structure of localised turbulence, which is called the turbulent stripe pattern, can be found in the form of stripe arrangement. The structure of the turbulent stripe pattern is an oblique laminar–turbulent banded pattern and is inclined with respect to the streamwise direction. We performed direct numerical simulation at a transitional Reynolds number and very low-rotation numbers, and focused on the turbulent stripe pattern in the plane Poiseuille flow subjected to spanwise system rotation. We captured the turbulent stripe pattern in a rotating channel flow and found the augmentation and diminution of the turbulent stripe pattern were affected by the spanwise rotation. The contents of the discussion are the spatial size of the turbulent stripe pattern on the basis of the instantaneous flow fields, the energy spectra, and various statistics relating to the spanwise velocity component that characterise the turbulent stripe pattern. The turbulent stripe pattern was found to contain kinetic energy that was larger in very weakly rotating flows than in the static system. It was also found that the magnitude of the spanwise secondary flow increases, while the quasi-laminar region is wider at a very lowrotation number. 相似文献
2.
《中国物理 B》2020,(2)
We investigate the flow patterns of irregular sand particles under avalanching mode in a rotating drum by using the spatial filtering velocimetry technique.By exploring the variations of velocity distribution of granular flow,we find a type of avalanching pattern of irregular sand particles which is similar to that of spherical particles flow.Due to the fact that the initial position of avalanche in this pattern locates at the middle of the drum and the avalanche propagates toward the edge area gradually,we named it as mid-to-edge avalanching pattern.Furthermore,we find another avalanching pattern which slumpS from the edge and propagates toward the opposite edge of the flow surface,named as edge-to-edge pattern.By analyzing the temporal and spatial characteristics of these two types of avalanching patterns,we discover that these two types of avalanche patterns are caused by that the avalanching particles constantly perturb the axial adjacent particles.Thus,the particles on the flow surface are involved in avalanching sequentially in order of the axial distance from the initial position. 相似文献
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利用气液两相流电导波动信号构建了流型复杂网络. 基于K均值聚类的社团探寻算法对该网络的社团结构进行了分析,发现该网络存在分别对应于泡状流、段塞流及混状流的三个社团,并且两个社团间联系紧密的点分别对应于相应的过渡流型. 基于复杂网络理论从全新的角度探讨了两相流流型复杂网络社团结构及统计特性问题,并取得了满意的流型识别效果,与此同时,在对该网络特性进一步分析的基础上,发现了对两相流流动参数变化敏感的相关复杂网络统计量,为更好地理解两相流流型动力学特性提供了参考.
关键词:
两相流流型
复杂网络
社团探寻算法
网络统计特性 相似文献
5.
Optical trapping and guiding using laser have been proven to be useful for non-contact and non-invasive manipulation of small objects such as biological cells, organelles within cells, and dielectric particles. We have numerically investigated so far the motion of a Brownian particle suspended in still water under the illumination of a speckle pattern generated by the interference of coherent light scattered by a rough object. In the present study, we investigate numerically the motion of a particle in a water flow under the illumination of a speckle pattern that is at rest or in motion. Trajectory of the particle is simulated in relation with its size, flow velocity, maximum irradiance, and moving velocity of the speckle pattern to confirm the feasibility of the present method for performing optical trapping and guiding of the particle in the flow. 相似文献
6.
V. Lepiller A. Goharzadeh A. Prigent I. Mutabazi 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(4):445-455
We have investigated the influence of a weak radial
temperature gradient in a wide gap and large aspect ratio
Couette-Taylor system. The inner cylinder is rotating and can be
heated or cooled, the outer cylinder is at rest and immersed in a
large thermal bath. We found that a radial temperature gradient
destabilizes the Couette flow leading to a pattern of traveling
helicoidal vortices occurring only near the bottom of the system.
The size of the pattern increases as the rotation frequency of the cylinder is increased. We
have characterized the spatiotemporal properties of the pattern and we have shown that it
behaves as a wall mode found in the simulation of the
complex Ginzburg-Landau equation with homogeneous boundary
conditions. 相似文献
7.
Results of a study of the flow rate — pressure head characteristics of a perforated membrane immersed in an oscillating liquid flow are reported; such characteristics need to be known when hydropneumodiodes are used as a pump. We show that the perforation pattern (or, more specifically, the number of perforated holes) affects just the rate of the liquid flow through membrane. 相似文献
8.
We report the results of experiments on electrically driven convection that occurs in a thin, freely suspended film of smectic A liquid crystal when an electric field is applied in the plane of the film. Convection in a vortex pattern is found above a well-defined critical voltage. The film behaves as a two-dimensional isotropic liquid: neither its thickness nor the director field are modified by the flow. We present measurements of the critical voltage at the onset of convection in two experimental configurations—one which allows the injection of charges into the film from the electrodes, and one which does not. When injection is present, the critical voltage for the onset of flow increases monotonically with increasing frequency of applied field. With no injection, there is no instability at DC and the critical voltage diverges there. The nature of the flow pattern observed at onset changes with frequency. Below a certain frequency the film flows in vortices that extend over the width of the film; above this frequency the flow is confined to two lines of smaller vortices localized along the electrodes. We present a simple discussion of the mechanisms which drive the convection. 相似文献
9.
We introduce a short review of chemically driven convection together with a series of our experiments on hydrodynamic instabilities induced by chemical waves excited in the batch reactor of a Belousov-Zhabotinsky reaction. Several unresolved phenomena are picked out and possible mechanisms are discussed extensively. Interesting features of these phenomena can be summarized as being caused by the ‘global and dynamic hydrodynamic pattern induced by chemical waves’. These chemically induced global pattern of hydrodynamic phenomena may not be simply explained by the reaction-diffusion-convection model based on Marangoni instability (surface tension-driven convection), which produces only a localized structure of the convection pattern. Observed flow waves show global and dynamic patterns of convection that generate a functional structure associated with hierarchical patterns appearing in the reaction-diffusion-convection system. In particular, we clarify the existence of a continuous stream of hydrodynamic flow with growing amplitude and its rotating direction. We find that the flow does not stabilize to a motionless state until the system has self-collapsed. This new picture of the flow waves requires a revision of the reaction-diffusion-convection model. The established flow structure can be regarded as a mixing and/or transport process to supply the substrate from the peripheral region to the centre of the chemical waves to sustain the reaction. This characteristic may be a function of the hierarchical structure. A new mechanism for the viscous-elastic feature of the gas-liquid interface is discussed in order to understand these curious phenomena of interest. 相似文献
10.
Vasquez DA 《Physical review letters》2004,93(10):104501
We predict a new type of instability induced by shear flow in chemical systems. A homogeneous steady state solution of a reaction-diffusion system loses stability in a Poiseuille flow. The instability appears as the speed of the flow increases beyond a certain threshold. This results in a steady pattern moving with the average fluid velocity. The chemical reaction consists of two species (activator and inhibitor) moving with identical velocities. Contrary to Turing's instability, the pattern arises when the activator has a higher diffusivity than the inhibitor. 相似文献
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We use a combination of numerical simulations and experiments to elucidate the structure of the flow of an electrically conducting fluid past a localized magnetic field, called magnetic obstacle. We demonstrate that the stationary flow pattern is considerably more complex than in the wake behind an ordinary body. The steady flow is shown to undergo two bifurcations (rather than one) and to involve up to six (rather than just two) vortices. We find that the first bifurcation leads to the formation of a pair of vortices within the region of magnetic field that we call inner magnetic vortices, whereas a second bifurcation gives rise to a pair of attached vortices that are linked to the inner vortices by connecting vortices. 相似文献
13.
S. S. Riaz S. Banarjee S. Kar D. S. Ray 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(4):509-515
We consider a reaction-diffusion system in crossed electric and magnetic fields lying on the reaction plane. It is shown that
a
charge separation along the direction normal to the reaction plane
resulting in a diffusional flux may cause a differential flow
induced chemical instability and stationary pattern formation on a
homogeneous steady state. This pattern is generically different from
a Turing pattern modified by the crossed fields. The special role of
magnetic field is emphasized. Our theoretical analysis is
corroborated by numerical simulation on a reaction-diffusion system
in three dimensions. 相似文献
14.
We present a 3-dimensional, linear analysis of electrohydrodynamic (EHD) roll instability in a nematic liquid crystal under
DC excitation. It is shown that the flexoelectric effect leads to a new symmetry of the flow pattern, viz. ahelical flow inoblique rolls. Our experimental observations agree with the theoretical predictions. 相似文献
15.
Duran J 《Physical review letters》2000,84(22):5126-5129
We observe ripples forming on the surface of a granular powder in a container submitted from below to a series of brief and distinct shocks. After a few taps, the pattern turns out to be stable against any further shock of the same amplitude. We find that the wavelength of the pattern is proportional to the amplitude of the shocks. Starting from considerations involving air flow through the porous granulate and avalanche properties, we build up a semiquantitative model which satisfactorily fits the set of experimental observations of either tapped or blown powder. 相似文献
16.
Acoustic streaming (AS) is the steady time-averaged flow generated by acoustic field, which has been widely used in enhancing mixing and particle manipulation. Current researches on acoustic streaming mainly focus on Newtonian fluids, while many biological and chemical solutions exhibit non-Newtonian properties. The acoustic streaming in viscoelastic fluids has been studied experimentally for the first time in this paper. We found that the addition of polyethylene oxide (PEO) polymer to the Newtonian fluid significantly altered the flow characteristics in the microchannel. The resulting acousto-elastic flow showed two modes: positive mode and negative mode. Specifically, the viscoelastic fluids under acousto-elastic flow exhibit mixing hysteresis features at low flow rates, and degeneration of flow pattern at high flow rates. Through quantitative analysis, the degeneration of flow pattern is further summarized as time fluctuation and spatial disturbance range reduction. The positive mode in acousto-elastic flow can be used for the mixing enhancement of viscoelastic fluids in the micromixer, while the negative mode provides a potential method for particle/cell manipulation in viscoelastic body fluids such as saliva by suppressing unstable flow. 相似文献
17.
We study the gravity induced instability of a liquid film formed below a plane grid which is used as a porous media in an original hydrodynamic experiment. The film is continuously supplied with a controlled flow rate. We give through a phase diagram the full spectrum of the different flow regimes and we investigate the dynamics of the observed structures. True secondary instabilities of a 2D periodic pattern are described. The control parameters are the flow rate and the viscosity. 相似文献
18.
We have studied the dynamics of avalanching wet granular media in a rotating drum apparatus. Quantitative measurements of the flow velocity and the granular flux during avalanches allow us to characterize novel avalanche types unique to wet media. We also explore the details of viscoplastic flow (observed at the highest liquid contents) in which there are lasting contacts during flow, leading to coherence across the entire sample. This coherence leads to a velocity-independent flow depth at high rotation rates and novel robust pattern formation in the granular surface. 相似文献
19.
We introduce thermometers to define the local temperature of an electronic system driven out-of-equilibrium by local ac fields. We discuss the behavior of the local temperature along the sample, showing that it exhibits spatial fluctuations following an oscillatory pattern. We show explicitly that the local temperature is the correct indicator for heat flow. 相似文献