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TRANSPORTATION OF passive scalar IN INHOMOGENEOUS TURBULENCE

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Acta Mechanica Sinica 2000年第1期16卷 21-28页

作者：崔桂香陈宇光张兆顺许春晓 L.Shao J.P.Bertoglio Department of Engineering Mechanics Tsinghua UniversityBeijing 100084China Laboratory of Fluid Mechanics and Acoustics Ecole Centrale de LyonFrance

The paper studies the transportation of passive scalar in the inhomogeneous turbulence by means of large eddy simulation. The prediction accuracy is verified by the well-known Comte-Bellot spectrum of the homogeneous turbulence. The mean transportation properties are predicted with satisfaction and the underestimation of the thermal flux by the phenomenological models has been disclosed. The high intermittence of the temperature fluctuations has been found in the inhomogeneous turbulence and it is the reason for the underestimation of turbulent thermal flux by the phenomenological model.

关键词： turbulence passive scalar large eddy simulation

Space-time correlations of passive scalar in Kraichnan model

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Theoretical & Applied Mechanics Letters 2023年第5期13卷 338-340页

作者： Ping-Fan Yang Liubin Pan Guowei He State Key Laboratory of Nonlinear Mechanics Institute of MechanicsChinese Academy of SciencesBeijing 100190China School of Engineering Sciences University of Chinese Academy of SciencesBeijing 100049China School of Physics and Astronomy Sun Yat-Sen UniversityZhuhai 519082China

We consider the two-point,two-time(space-time)correlation of passive scalar R(r,τ)in the Kraichnan model under the assumption of homogeneity and *** the fine-gird PDF method,we find that R(r,τ)satisfies a diffusion equation with constant diffusion coefficient determined by velocity variance and molecular *** can be expressed in terms of the two-point,one time correlation of passive scalar,i.e.,R(r,0).Moreover,the decorrelation o R(k,τ),which is the Fourier transform of R(r,τ),is determined byR(k,0)and a diffusion kernal.

关键词： Space-time correlation passive scalar Kraichnan model

Influence of velocity spatiotemporal correlations on the anomalous scaling exponents of passive scalars

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Chinese Physics B 2009年第12期18卷 5117-5122页

作者：张晓强王光瑞陈式刚 Graduate School of China Academy of Engineering Physics Center for Nonlinear Studies Institute of Applied Physics and Computational Mathematics

In this paper, we consider spatial-temporal correlation functions of the turbulent velocities. With numerical simulations on the Gledzer-Ohkitani-Yamada （GOY） shell model, we show that the correlation function decays exponentially. The advecting velocity field is regarded as a colored noise field, which is spatially and temporally correlative. For comparison, we are also given the scaling exponents of passive scalars obtained by the Gaussian random velocity field, the multi-dimensional normal velocity field and the She-Leveque velocity field, introduced by She, et al. We observe that extended self-similarity sealing exponents H（p）/H（2） of passive scalar obtained by the colored noise field are more anomalous than those obtained by the other three velocity fields.

关键词： shell models passive scalar anomalous scaling exponents

Influence of Velocity Shell Correlations on Anomalous Scaling Exponents of passive scalars in Shell Models

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Communications in Theoretical Physics 2008年第7期50卷 211-214页

作者： ZHANG Xiao-Qiang WANG Guang-Rui CHEN Shi-Gang Graduate School of China Academy of Engineer Physics P.O. Box 8009（28） Beijing 100088 China Center for Nonlinear Studies Institute of Applied Physics and Computational Mathematics P.O. Box 8009（28） Beijing 100088 China

We propose a new approach to the old-standing problem of the anomaly of the scaling exponents of passive scalars of turbulence. Different to the original problem, the distribution function of the prescribed random velocity field is multi-dimensional normal and delta-correlated in time. Here, our random velocity field is spatially correlative. For comparison, we also give the result obtained by the Gaussian random velocity field without spatial correlation. The anomalous scaling exponents H（p） of passive scalar advected by two kinds of random velocity above are determined for structure function up to p= 15 by numerical simulations of the random shell model with Runge-Kutta methods to solve the stochastic differential equations. We observed that the H（p）＇s obtained by the multi-dimeasional normal distribution random velocity are more anomalous than those obtained by the independent Gaussian random velocity.

关键词： shell models passive scalar distribution function

Probability Distribution Function of passive scalars in Shell Models

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Communications in Theoretical Physics 2008年第4期49卷 1033-1038页

作者： ZHANG Xiao-Qiang WANG Guang-Rui CHEN Shi-Gang Department of Physics Hebei Normal University Shijiazhuang 050016 China Graduate School of the China Academy of Engineering Physics P.O. Box 8009（28） Beijing 100088 China Center for Nonlinear Studies Institute of Applied Physics and Computational Mathematics Beijing 100088 China

A shell-model version of passive scalar problem is introduced, which is inspired by the model of K. Ohkitani and M. Yakhot [K. Ohkitani and M. Yakhot, Phys. Rev. Lett. 60 （1988） 983; K. Ohkitani and M. Yakhot, Prog. Theor. Phys. 81 （1988） 329]. As in the original problem, the prescribed random velocity field is Gaussian and 5 correlated in time. Deterministic differential equations are regarded as nonlinear Langevin equation. Then, the Fokker-Planck equations of PDF for passive scalars are obtained and solved numerically. In energy input range （n 〈 5, n is the shell number.）, the probability distribution function （PDF） of passive scalars is near the Gaussian distribution. In inertial range （5≤ n ≤ 16） and dissipation range （n ≥ 17）, the probability distribution function （PDF） of passive scalars has obvious intermittence. And the scaling power of passive scalar is anomalous. The results of numerical simulations are compared with experimental measurements.

关键词： shell model passive scalar distribution function

Anomalous scaling in a non-Gaussian random shell model for passive scalars

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Chinese Physics B 2007年第10期16卷 2848-2854页

作者：赵英奎陈式刚王光瑞 Graduate School of China Academy of Engineering Physics Beijing 100088 China Center for Nonlinear Studies Institute of Applied Physics and Computational Mathematics Beijing 100088 China

In this paper, we have introduced a shell-model of Kraichnan＇s passive scalar problem. Different from the original problem, the prescribed random velocity field is non-Gaussian and σ correlated in time, and its introduction is inspired by She and Levveque （Phys. Rev. Lett. 72, 336 （1994））. For comparison, we also give the passive scalar advected by the Gaussian random velocity field. The anomalous scaling exponents H（p） of passive scalar advected by these two kinds of random velocities above are determined for structure function with values of p up to 15 by Monte Carlo simulations of the random shell model, with Gear methods used to solve the stochastic differential equations. We find that the H（p） advected by the non-Gaussian random velocity is not more anomalous than that advected by the Gaussian random velocity. Whether the advecting velocity is non-Gaussian or Gaussian, similar scaling exponents of passive scalar are obtained with the same molecular diffusivity.

关键词： scaling shell model She and Leveque (SL) model non-Gaussian passive scalar

Large-eddy-simulation of 3-dimensional Rayleigh-Taylor instability in incompressible fluids

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Science China Mathematics 2002年第1期45卷 95-106页

作者：王丽丽李家春谢正桐 Inst. Appl. Phys. and Compl. Math. Beijing 100088 China LNM Institute of Mechanics Chinese Academy of Science Beijing 100080 China

The 3-dimensional incompressible Rayleigh-Taylor instability is numerically studied through the large-eddy-simulation ( LES) approach based on the passive scalar transport model. Both the instantaneous velocity and the passive scalar fields excited by sinusoidal perturbation and random perturbation are simulated. A full treatment of the whole evolution process of the instability is addressed. To verify the reliability of the LES code, the averaged turbulent energy as well as the flux of passive scalar are calculated at both the resolved scale and the subgrid scale. Our results show good agreement with the experimental and other numerical work. The LES method has proved to be an effective approach to the Rayleigh-Taylor instability.

关键词： Rayleigh-Taylor instability large-eddy-simulation passive scalar turbulent mixing

Effect of Oscillation Structures on Inertial-Range Intermittence and Topology in Turbulent Field

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Communications in Computational Physics 2016年第1期19卷 251-272页

作者： Kun Yang Zhenhua Xia Yipeng Shi Shiyi Chen State Key Laboratory of Turbulence and Complex Systems Center for Applied Physics and TechnologyCollege of EngineeringPeking UniversityBeijing 100871P.R.China Collaborative Innovation Center of Advanced Aero-Engine Beijing 100191P.R.China

Using the incompressible isotropic turbulent fields obtained from direct numerical simulation and large-eddy simulation,we studied the statistics of oscillation structures based on local zero-crossings and their relation with inertial-range intermittency for transverse velocity and passive *** results show that for both the velocity and passive scalar,the local oscillation structures are statistically scaleinvariant at high Reynolds number,and the inertial-range intermittency of the overall flow region is determined by the most intermittent structures characterized by one local *** flow patterns conditioned on the oscillation structures are characterized by the joint probability density function of the invariants of the filtered velocity gradient tensor at inertial *** demonstrate that the most intermittent regions for longitudinal velocity tend to lay at the saddle area,while those for the transverse velocity tend to locate at the vortex-dominated *** connection between the ramp-cliff structures in passive scalar field and the corresponding saddle regions in the velocity field is also verified by the approach of oscillation structure classification.

关键词： Oscillation structure intermittency transverse velocity passive scalar

Stirring by anisotropic squirming

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Theoretical & Applied Mechanics Letters 2022年第4期12卷 286-293页

作者： Zhi Lin Sirui Zhu Lingyun Ding School of Mathematical Sciences Zhejiang UniversityHangzhouZhejiang 310027China Department of Mathematics University of North CarolinaChapel HillNC 27599United States

We consider a fluid stirred by the locomotions of squirmers through it and generalize the stochastic hydrodynamic model proposed by Thiffeault and Childress,***.A(2010)and Lin et al.,*** Mech.(2011)to the case in which the swimmers move in anisotropically random directions.A non-diagonal effective diffusivity tensor is derived with which the diffusive preference of a passive particle along any given direction can be computed to provide more details of the phenomena beyond scalar *** further identify a fraction from the orthogonal decomposition of the drift-induced particle displacement to distinguish the underlying nonlinear mixing mechanism for different types of *** simulations verify the analytical results with explicit examples of prescribed,anisotropic stirring *** also connect our formulation to several measures used in clinical medical research such as diffusion tensor imaging where anisotropic diffusion has a significant consequence.

关键词： Mixing and transport passive scalar Anisotropic diffusion