大气湍流光学参数分析

利用两种不同大气湍流结构常数模型,讨论了不同高度的湍流对大气湍流光学参数的影响。通过理论计算得出:相干长度和对数振幅起伏方差主要由低层大气湍流决定,而等晕角、倾斜等晕角、格林伍德频率和泰勒频率由对流层顶附近的高层湍流决定。分析了垂直高度30 km以下的3部分大气湍流对等晕角的贡献比例,在给定的不同强度湍流下,对流层顶附近的高层大气湍流贡献比例都大于25％,而低层大气湍流的贡献比例都小于3%。     

Path-averaged differential meter of atmospheric turbulence parameters

A path-averaged differential meter of the structure constant of the atmospheric refractive index, C _n ², has been developed and tested. The results of a model numerical experiment on measuring C _n ² and the horizontal component of average wind velocity transverse to the path are reported.     

A study on turbulence modulation via an analysis of turbulence anisotropy-invariants

We investigate the turbulence modulation by particles in a turbulent two-phase channel flow via an analysis of turbulence anisotropy-invariants. The fluid turbulence is calculated by a large eddy simulation with a point-force two-way coupling model and particles are tracked by the Lagrangian trajectory method. The channel turbulence follows the two-component turbulence state within the viscous sub-layer region and outside the region the turbulence tends to follow the right curve of the anisotropy-invariant....     

Large-eddy simulations of fluid and magnetohydrodynamic turbulence using renormalized parameters

In this paper a procedure for large-eddy simulation (LES) has been devised for fluid and magnetohydrodynamic turbulence in Fourier space using the renormalized parameters. The parameters calculated using field theory have been taken from recent papers by Verma [1,2]. We have carried out LES on 64³ grid. These results match quite well with direct numerical simulations of 128³. We show that proper choice of parameter is necessary in LES.     

海洋湍流中自适应光学成像系统特征参量研究

随着水下光通信、传感和激光雷达等应用的发展,研究水下光学系统成像特性具有重要意义.本文研究了海洋湍流对自适应光学成像系统特征参量(如Strehl比、Greenwood时间常数和等晕角)的影响.推导出了海洋湍流中短曝光成像Strehl比的近似解析表达式,并证明:除了在近场D_G/r_0=1附近外(D_G和r_0分别为光学系统的光瞳直径和海洋湍流中可见参数),该近似公式均可保证足够的精度.此外,还得到了海洋湍流中Greenwood时间常数和等晕角的表达式.研究表明:随着海水盐度变化引起的海洋湍流逐渐占主导地位时,这三个特征参量值均减小;随着海水湍流动能耗散率的减小或海水湍流温度方差耗散率的增大,这三个特征参量值也均减小.本文研究结果对工作于水下湍流环境中自适应光学成像系统应用具有理论参考意义.     

Express analysis of spectra in precision experiments

Some precision experiments require several tens of hours for measurements. In this case, it is important to take into account possible drift of the detection system parameters in time. An express analysis program has been developed for early detection of significant distortions in recorded spectra, their filtration, and correction of results. Original Russian Text ? N.A. Gundorin, N.D. Dikoussar, N.G. Maznyj, L.B. Pikelner, I.M. Salamatin, M.I. Tsulaja, 2009, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2009, Vol. 73, No. 2, pp. 261–263.     

用常规气象参数估算光学湍流廓线方法的比较

采用美国SPARC数据中心提供的高分辨率无线电探空数据,运用Tatarski公式,对由外尺度或湍流能量耗散率结合常规气象参数估算的折射率结构常数结果进行了比较,间接证明了Sterenborg将外尺度选取1 m时的合理性。并比较了Coulman和Dewan两个外尺度经验公式估算的折射率结构常数。对比分析表明：利用外尺度或湍流能量耗散,结合常规气象参数,都能够估算出折射率结构常数。因湍流能量耗散率观测十分困难,该方法的合理性和代表性需待实验检验。Coulman的外尺度公式只是简单的经验公式,其普适性也需实验检验。而Dewan的外尺度公式中含有实测风速参数,由对流层和平流层不同区域的外尺度公式估算的折射率结构常数相对合理。     

用常规气象参数估算光学湍流廓线方法的比较

 采用美国SPARC数据中心提供的高分辨率无线电探空数据,运用Tatarski公式,对由外尺度或湍流能量耗散率结合常规气象参数估算的折射率结构常数结果进行了比较,间接证明了Sterenborg将外尺度选取1 m时的合理性。并比较了Coulman和Dewan两个外尺度经验公式估算的折射率结构常数。对比分析表明：利用外尺度或湍流能量耗散,结合常规气象参数,都能够估算出折射率结构常数。因湍流能量耗散率观测十分困难,该方法的合理性和代表性需待实验检验。Coulman的外尺度公式只是简单的经验公式,其普适性也需实验检验。而Dewan的外尺度公式中含有实测风速参数,由对流层和平流层不同区域的外尺度公式估算的折射率结构常数相对合理。     

Visibility graph analysis of wall turbulence time-series

The spatio-temporal features of the velocity field of a fully-developed turbulent channel flow are investigated through the natural visibility graph (NVG) method, which is able to fully map the intrinsic structure of the time-series into complex networks. Time-series of the three velocity components, $(u,v,w)$, are analyzed at fixed grid-points of the whole three-dimensional domain. Each time-series was mapped into a network by means of the NVG algorithm, so that each network corresponds to a grid-point of the simulation. The degree centrality, the transitivity and the here proposed mean link-length were evaluated as indicators of the global visibility, inter-visibility, and mean temporal distance among nodes, respectively. The metrics were averaged along the directions of homogeneity ($x,z$) of the flow, so they only depend on the wall-normal coordinate, $y^{+}$. The visibility-based networks, inheriting the flow field features, unveil key temporal properties of the turbulent time-series and their changes moving along $y^{+}$. Although intrinsically simple to be implemented, the visibility graph-based approach offers a promising and effective support to the classical methods for accurate time-series analyses of inhomogeneous turbulent flows.     

Variation analysis of turbulence resistance and angular spreading for partially coherent beam in turbulence

A new factor M is proposed to characterize the similarity of the behavior of a partially coherent beam (PCB) to its coherent counterpart when propagating through atmospheric turbulence. It is shown that there exists a boundary in the range of the source coherent length. The decreasing rates of free space angular spreading and of turbulence distance with the source coherent length are different before and after the coherent length arriving at the boundary value, by which the change trend of M can be concluded.     

Generalized Stokes parameters of random electromagnetic vortex beams propagating through atmospheric turbulence

By using the extended Huygens–Fresnel principle, the analytical expressions for the generalized Stokes parameters of random electromagnetic Gaussian Schell-model (GSM) vortex beams propagating through atmospheric turbulence are derived, and used to study the changes in spectral Stokes parameters of random electromagnetic GSM vortex beams in atmospheric turbulence and to compare the results of random electromagnetic GSM vortex-free beams. The influence of atmospheric turbulence on the spectral Stokes parameters is analyzed. The validity of our results is interpreted physically.     

海洋湍流中光波特征参量和短期光束扩展的研究

Nikishov等建立的海洋湍流功率谱模型中,假设了海水有着稳定的分层.但是,实际海水通常不是稳定分层的,温度与盐度的涡流扩散率是不相等的.2017年,Elamassie等建立了考虑这些因素的更合理的海洋湍流功率谱模型.湍流介质中光波空间相干长度等基本特征参量在表征湍流强度和光传输相位校正技术等方面起着重要作用.本文基于Elamassie海洋湍流功率谱模型,重新推导出了海洋湍流中光波结构函数、光波空间相干长度和Fried参数的解析公式,并校验了所得公式的正确性.研究发现：当温度变化引起的光学湍流占主导地位时,Nikishov海洋湍流功率谱模型把湍流强度低估了;当盐度变化引起的光学湍流占主导地位时,Nikishov海洋湍流功率谱模型把湍流强度高估了.基于Elamassie海洋湍流功率谱模型,本文推导出了高斯光束短期光束扩展的半解析公式,并验证了其正确性.研究还表明：海水稳定分层与否,短期光束扩展差异很大.本文研究结果对水下湍流环境中的光通信、成像和传感等应用具有重要意义.     

Speckle photography applied to statistical analysis of turbulence

A speckle photographic technique is used for visualizing the planar distribution of the refractive deflection angles of light transmitted through the compressible turbulent flow. Both double and single (prolonged) exposure speckle photography are applied for statistical analysis of such flows. Using single (prolonged) exposure speckle photography (SPESP), instantaneous quantitative measurement of 2-D distribution of turbulence intensity in a flame is performed. Anisotropy of turbulence is visualized by a diffraction halo form and quantitatively evaluated by measuring the diffraction halo diameters. Using double exposure speckle photography (DESP), quantitative visualization of the planar distribution of the refractive deflection angles of the light transmitted through the compressible turbulent flow is done. Turbulent structures are visible in the patterns of the deflection angles isolines. The 2-D correlation functions of these deflection angles are constructed and analyzed. The 3-D density correlation functions are evaluated using the Erbeck–Merzkirch integral transformation.     

Two-parameter expansion in the renormalization-group analysis of turbulence

The renormalization of the solution of the Navier-Stokes equation for randomly stirred fluid with long-range correlations of the driving force is analysed near two dimensions. It is shown that a local term must be added to the correlation function of the random force for the correct renormalization of the model at two dimensions. The interplay of the short-range and long-range terms in the large-scale behaviour of the model is analysed near two dimensions by the field-theoretic renormalization group. A regular expansion in 2ε=d-2 and δ=2-λ is constructed, whered is the space dimension and λ the exponent of the powerlike correlation function of the driving force. It is shown that in spite of the additional divergences, the asymptotic behaviour of the model near two dimensions is the same as in higher dimensions, contrary to recent conjectures based on an incorrect renormalization procedure.     

Two-parameter expansion in the renormalization-group analysis of turbulence

The renormalization of the solution of the Navier-Stokes equation for randomly stirred fluid with long-range correlations of the driving force is analysed near two dimensions. It is shown that a local term must be added to the correlation function of the random force for the correct renormalization of the model at two dimensions. The interplay of the short-range and long-range terms in the large-scale behaviour of the model is analysed near two dimensions by the field-theoretic renormalization group. A regular expansion in 2ε=d-2 and δ=2-λ is constructed, whered is the space dimension and λ the exponent of the powerlike correlation function of the driving force. It is shown that in spite of the additional divergences, the asymptotic behaviour of the model near two dimensions is the same as in higher dimensions, contrary to recent conjectures based on an incorrect renormalization procedure.     

Estimation of turbulence spectra parameters from log-amplitude fluctuations spectra of an optical wave

From the general formula for the temporal frequency log-amplitude fluctuations spectra the asymptotic expressions are found, valid for the geometric and wave approximations. A comparison of the plane and spherical wave formulas with those valid for the beam wave is made in all frequency regions. The difference between the on-axis and off-axis beam spectra is presented. The possibility of estimating from the log-amplitude scintillations the inner and outer scales of turbulence together with the exponent of turbulence spectra in the subrange is briefly discussed.     

基于气象参数戈壁沙漠地区近地面大气湍流建模

提出一种适合戈壁沙漠地区的近地面大气湍流模型。通过测量近地面层不同高度处温度、湿度、压强和风速等常规气象参数,结合模型可给出近地面层大气湍流强度。模型计算的近地面层大气湍流强度通常白天值最大,中午前后出现较宽的最大值区间,在日出时段和日落时段出现较明显的最小值,夜间呈不规则变化,该结果能够很好地反映近地面层大气湍流强度的变化特性。在影响大气湍流强度变化的参数中,大气温度的变化趋势直接影响着大气湍流强度的变化：通常白天大气温差较高时,大气湍流强度较强;大气温差较低时,大气湍流强度较弱;大气温差起伏较大的时刻,大气湍流强度的变化也会较大,大气温差起伏趋势与大气湍流强度变化趋势有相似之处。