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.     

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。     

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.     

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.     

Performance analysis of non-line-of-sight ultraviolet communication through turbulence channel

The bit error rate performance of non-line-of-sight ultraviolet communication through atmospheric turbulence is studied. The communication performance degradation under different strengths of turbulence is evaluated.Particularly, under strong turbulence conditions, the communication distance can be shortened by 30%, or at a given distance the communication rate can be reduced by half than the counterpart of no turbulence.     

湍流气象探空仪的研制及其性能分析

 最新研制的湍流气象探空仪是将温度脉动仪附加在常规气象探空仪上,实现了两路折射率结构常数、温湿压常规气象参数、温度谱等测量。通过在合肥和长春的实验表明该系统具有较高的测量精度和稳定性,在高空低温动态条件下探空仪系统噪声与温度脉动仪地面常温静态条件下的噪声相当。探空系统噪声引起的等效折射率结构常数小于2×10^-18 m^-2/3。能服务于激光传输、大气质量评价及天文台选址等相关领域对大气光学湍流研究的需要。     

Nonlinear dynamical analysis of turbulence in a stable cloud layer

An eight mode truncated spectral model based on Burgers' approximation to the one-dimensional Navier-Stokes equations is used to compute the Lyapunov dimension of the dynamical attractor for turbulence in a stable cloud layer. The model results are compared with the correlation dimension obtained earlier from a time series of radar Doppler and reflectivity signals from a turbulent layer in a marine stratus cloud. The analysis supports a weak coupling explanation for the lower correlation dimension found for the reflectivity time series compared with that for the Doppler time series. Turbulent Prandtl number emerges from the analysis as a flow parameter which can enlarge the dimension of the model's dynamical attractor, but the attractor dimension computed for the model remains lower than the radar Doppler correlation dimension. Linear stability analysis of the model's equilibrium states suggests that a nontruncated version of the model will possess an attractor which is also of lower dimension than the radar Doppler correlation dimension. (c) 1995 American Institute of Physics.