On a Shock Front in Burgers Turbulence

We investigate how chaos propagates in the solution of Burgers equation _t u+u _x u=0 with initial condition u(,0) distributed as a white noise on and 0 on . We describe the evolution of the shock front that travels to the left. Asymptotics are given for both large and small time t.     

On the Landau–Lifschitz Degrees of Freedom in 2-D Turbulence

We show that if the Kraichnan theory of fully developed turbulence holds, then the Landau–Lifschitz degrees of freedom is bounded (up to a logarithmic term) by G ^1/2, where G is the Grashof number.     

液晶大气湍流模拟器

提出平行取向液晶器件作为大气湍流模拟器(ATS)的应用,研制出平行排列TFT型二维阵列液晶湍流模拟器(LC ATS)．基于Zernike多项式模拟大气湍流的理论,在Zygo干涉仪上,利用此湍流模拟器产生Zernike模式面形,能够很好的产生Zernike多项式的前2~8项模式面形．并且选取前231项Zernike模式,进行湍流的计算模拟与液晶湍流模拟器的实验模拟,计算模拟与实验模拟的湍流结果比较接近,说明此类型液晶湍流模拟器可以模拟大气湍流.     

Gibbsian Hypothesis in Turbulence

We show that Kolmogorov multipliers in turbulence cannot be statistically independent of others at adjacent scales (or even a finite range apart) by numerical simulation of a shell model and by theory. As the simplest generalization of independent distributions, we suppose that the steady-state statistics of multipliers in the shell model are given by a translation-invariant Gibbs measure with a short-range potential, when expressed in terms of suitable spin variables: real-valued spins that are logarithms of multipliers and XY-spins defined by local dynamical phases. Numerical evidence is presented in favor of the hypothesis for the shell model, in particular novel scaling laws and derivative relations predicted by the existence of a thermodynamic limit. The Gibbs measure appears to be in a high-temperature, unique-phase regime with paramagnetic spin order.     

Turbulence over arrays of obstacles in low temperature helium gas

Turbulence produced in low temperature helium gas flowing over arrays of rectangular- and triangular-shaped blunt obstacles is investigated experimentally. The set-up allows both low fluctuation rates (down to 8%), and high microscale Reynolds numbers, (up to 1 150). The forced Kolmogorov equation is found to apply accurately. Similar to another flow configuration (counter rotating flow case [1]), the analysis of the flatness factor evolution with the Reynolds number reveals a transitional behavior around 650. Received 26 August 1999 and Received in final form 28 August 2000     

Turbulence noise

We show that the large-eddy motions in turbulent fluid flow obey a modified hydrodynamic equation with a stochastic turbulent stress whose distribution is a causal functional of the large-scale velocity field itself. We do so by means of an exact procedure of statistical filtering of the Navier-Stokes equations, which formally solves the closure problem, and we discuss the relation of our analysis with the decimation theory of Kraichnan. We show that the statistical filtering procedure can be formulated using field-theoretic path-integral methods within the Martin-Siggia-Rose (MSR) formalism for classical statistical dynamics. We also establish within the MSR formalism a least-effective-action principle for mean turbulent velocity profiles, which generalizes Onsager's principle of least dissipation. This minimum principle is a consequence of a simple realizability inequality and therefore holds also in any realizable closure. Symanzik's theorem in field theory—which characterizes the static effective action as the minimum expected value of the quantum Hamiltonian over all state vectors with prescribed expectations of fields—is extended to MSR theory with non-Hermitian Hamiltonian. This allows stationary mean velocity profiles and other turbulence statistics to be calculated variationally by a Rayleigh-Ritz procedure. Finally, we develop approximations of the exact Langevin equations for large eddies, e.g., a random-coupling DIA model, which yield new stochastic LES models. These are compared with stochastic subgrid modeling schemes proposed by Rose, Chasnov, Leith, and others, and various applications are discussed.     

Sensing Atmospheric Turbulence by Laser Radiation

Atmospheric turbulence sensing by lateral fluctuations of thin beams is described. Practical use of correlation functions of lateral fluctuations to investigate the refractive index spectrum and its parameters, inner and outer scale and structure constant, is presented. A “maximum” method is also shown to derive the inner scale independently of the other parameters, without either knowing much of the turbulence or solving an inverse problem.Presented at the International Commission for Optics Topical Meeting, Kyoto, 1994.     

On the Inertial Range Bounds of K-41-like Magnetohydrodynamics Turbulence

The spectral slope of magnetohydrodynamic (MHD) turbulence varies depending on the spectral theory considered; −3/2 is the spectral slope in Kraichnan–Iroshnikov–Dobrowolny (KID) theory, −5/3 in Marsch–Matthaeus–Zhou and Goldreich–Sridhar theories, also called Kolmogorov-like (K-41-like) MHD theory, the combination of the −5/3 and −3/2 scales in Biskamp, and so on. A rigorous mathematical proof to any of these spectral theories is of great scientific interest. Motivated by the 2012 work of A. Biryuk and W. Craig (Physica D 241(2012) 426–438), we establish inertial range bounds for K-41-like phenomenon in MHD turbulent flow through a mathematical rigor; a range of wave numbers in which the spectral slope of MHD turbulence is proportional to −5/3 is established and the upper and lower bounds of this range are explicitly formulated. We also have shown that the Leray weak solution of the standard MHD model is bonded in the Fourier space, the spectral energy of the system is bounded and its average over time decreases in time.     

可激发介质湍流的耦合同步及控制

利用相互耦合方法实现了两个处于湍流态的可激发系统的精确同步，给出了确定耦合系数的方法，计算了最大横向Lyapunov指数.并基于相互耦合，将处于湍流态的可激发系统与两个处于不同状态的可激发系统进行相互耦合，实现了用两种不同方法对湍流态的稳定控制. 关键词： 可激发介质 湍流控制 同步 耦合系数     

标量湍流的能量传输特性

应用直接数值模拟数据,从标量湍流传输的三波关系出发,进行湍流及标量湍流传输谱的多尺度分析,研究不同尺度间的能量传输性质,证实标量能量的传输与湍动能传输具有不同性质,大尺度速度脉动对标量传输有较大贡献,尤其是与标量小尺度脉动的相互作用,使标量模拟需要有比速度场更高的网格分辨率;并发现标量湍流的能量传输具有明显的非局部性;另外,定义了能量传输系数,发现在相同的Re数和Pe数条件下,标量湍流的对流惯性较速度脉动的惯性子区宽.     

湍流大气成像系统分辨率的研究

采用基于Kolmogorov 1941串级湍流模型建立的调制湍流折射率谱模型、简单透镜成像系统传递函数的高斯函数近似和平方近似,从理论上分析了大气成像系统的光学传递函数,研究了有限湍流尺度(湍流内、外尺度)对湍流大气中成像系统光学分辨率的影响。给出了成像系统长曝光光学传递函数和积分分辨率的近似解析关系。结果表明在采用大孔径成像系统成像时,应该考虑湍流尺度对大气系统成像的作用。     

Beyond Scaling and Locality in Turbulence

An analytic perturbation theory is suggested in order to find finite-size corrections to the scaling power laws. In the frame of this theory it is shown that the first order finite-size correction to the scaling power laws has following form , where η is a finite-size scale (in particular for turbulence, it can be the Kolmogorov dissipation scale). Using data of laboratory experiments and numerical simulations it is shown shown that a degenerate case with α ₀=0 can describe turbulence statistics in the near-dissipation range r > η, where the ordinary (power-law) scaling does not apply. For moderate Reynolds numbers the degenerate scaling range covers almost the entire range of scales of velocity structure functions (the log-corrections apply to finite Reynolds number). Interplay between local and non-local regimes has been considered as a possible hydrodynamic mechanism providing the basis for the degenerate scaling of structure functions and extended self-similarity. These results have been also expanded on passive scalar mixing in turbulence. Overlapping phenomenon between local and non-local regimes and a relation between position of maximum of the generalized energy input rate and the actual crossover scale between these regimes are briefly discussed. PACS: 47.27.-i, 47.27.Gs.     

不同湍流模型对热等离子体射流模拟的影响

本文应用大气压等离子体射流传热与流动的三维数学模型,在相同初始条件下,计算得到了采用不同湍流模型时氩等离子体射流对称轴线上的温度、速度及空气质量分数分布,并与文献中同等条件下的实验结果进行了比较,结果表明采用标准κ-ε模型和Realizableκ-ε模型时与实验结果相差较大,而采用RNGκ-ε湍流模型时模拟结果与实验数...     

Compressible Flow: Turbulence at the Surface

In a study of compressible flow, we have tracked the motion of particles that float on a turbulent body of water. The second moment of longitudinal velocity differences scales as in incompressible flow. However the separation R ²(t) of particle pairs does not vary in time according to the Richardson–Kolmogorov prediction R ²(t)t ³. As expected, the self diffusion d ²(t) shows a crossover between ballistic motion d ²(t)t ² at small t and uncorrelated motion d ²(t)t in the longtime limit.     

聚焦光束模拟湍流效应自适应光学补偿实验

报道了聚焦光束传输模拟湍流效应校正实验研究，描述了短曝光情况下，补偿效率积分概率的意义，给出了本套自适应光学系统补偿效率与变形镜驱动器的光束发射直径上的平均间中距和湍流相干长度的系统定标关系。     

Energy Transfer in Spectra of the d-Dimensional Past Grid Turbulence

Free decay theory of the homogeneous and isotropic developed turbulence isconsidered in the d-dimensional case. The basic quantities under our consideration are the kinetic energy spectrum E(k,t) and energy transfer spectrum T(k,t) as functions of wave number k and decay time t. Starting point for studying E and T represents their adaptation from the stationary model which predicts the Kolmogorov spectrum which is multiplicatively dependent on an unknown scaling function F. In order to study the spectra of decaying turbulence both parameters l and εɛ are supposed to be dependent on t. Formerly derived basic integro–differential equation for F (by Adzhemyan, et al., 1998) has been here solved numerically in the dimension interval d∈(2, 3) for two cases of the Saffman invariant and the Loitsyansky integral fixing an arbitrary theor parameter α (α ⩵ 2 and 4, correspondingly). The energy transfer spectrum T(k) has been analyzed for several dimensions d≤3 showing the presence of integration regions in the wavenumber space where an inverse energy cascade can occur. PACS numbers: 47.27.ef, 47.11.-j, 47.27.er     

Turbulence investigation in a laboratory model of the ascending aorta

This study aims to investigate turbulence inside a model of the human ascending aorta as a function of the main flow control parameters. For this purpose, we performed a two-dimensional in vitro investigation of the pulsatile flow inside a laboratory model of a healthy aorta by varying both the Reynolds and Womersley numbers. Our findings indicate that the velocity fluctuations become significant particularly during the deceleration phase of the flow, reach the maximum near the systolic peak and then decay during the rest of the diastole phase. Higher levels of turbulence were recovered for increasing Stroke Volumes, in particular maxima of Turbulent Kinetic Energy occurred in the bulk region while higher values of Reynolds shear stresses were found in correspondence of the sinus of Valsalva.     

Poloidal Structure of the Turbulence and the Turbulent Flux During Edge Plasma Biasing in the Castor Tokamak

The poloidal structure of the turbulence and the turbulent particle flux in the scrape-off layer (SOL) of the CASTOR tokamak are analysed by means of a poloidal ring of 124 probes distributed uniformly along the whole poloidal circumference. Fluctuation measurements are performed in standard ohmic regime as well as in discharges when a biased electrode is inserted either into the SOL or deeper into the confinement region. It is found that in both cases a strongly sheared radial electric field is created in the SOL, which de-correlates the density and radial velocity fluctuations and reduces their levels. Consequently, the turbulent flux is reduced. However, no phase shift is observed between density and radial velocity fluctuations. When the electrode is localized in the confinement region, all the above effects are less pronounced because of a smaller shear. In addition, the increase of the E × B velocity at biasing leads in both cases to the formation of oscillations in the temporal correlation function. These oscillations are specifically associated to the poloidal mode (m = q), which is created for a limited time and rotates poloidally. This mode does not modify the phase between density and radial velocity fluctuations and has no further effect on the turbulent flux.