Development and Testing of a Methodology for Assessing of the Correlation Velocity Measurements’ Accuracy for the Hydrodynamic Investigations of the Turbulent Coolant Flow in Nuclear Reactor Elements

The correlation method of the coolant flow measuring is widely used in research practice including for studying of turbulent coolant flows in scale models of elements of nuclear power plants. The aim of this work was to develop a technique for assessing the effect of noise recorded by a measuring system on the flow rate readings obtained using the correlation method.A technique to assess the effect of noise as well as the relative position and acquisition period of sensors is presented. An insignificant concentration of a salt solution (NaCl or Na2SO4 ) is used as a passive impurity which creates a conductivity gradient of the medium recorded by a conductometric system. Turbulent pulsations at the interface between two concurrent isokinetic flows in a channel with a square cross section are used as the signal source for the correlational algorithm.Paper presents the values of the turbulence′s transport time between spatial conductometers, the results of estimating the spectral power density and band of the recorded signal and also the signalto-noise ratios of the measuring system obtained on their basis which are subsequently used to estimate the confidence interval of the transport time.As a result of measurements the relationship between the confidence interval value and the signal length were obtained. The measurements which were carried out at different relative positions of conductometers make it possible to make a conclusion about an increase in the spectral width of the signal and, as a consequence, a decrease in the length of the confidence interval with increasing of distance between sensors.The presented work is an approbation of this approach for its application as part of an experimental model of a nuclear reactor in order to determine per-channel flow rates in the channels of the core simulator using mesh conductometric sensors taking into account the effect of noise.

ECONOMIC ALGORITHM FOR EVALUATING THE PARAMETER FOR THE GLOBAL MODEL OF TRANSFER AND DIFFUSION

The paper considers the data assimilation algorithm for the global model of transport and diffusion. An algorithm is proposed for finding an estimate of an unknown parameter for the transport and diffusion problem of a passive impurity. Various options for data assimilation algorithms with unknown parameters are described: searching for a joint assessment of a system and a parameter and evaluating only a parameter. The problems of implementing data assimilation algorithms and methods for solving them are shown. The ensemble algorithm of the Kalman filter is given, the economical use of it is argued. An important property of the proposed algorithm is its locality - the algorithm can be applied locally in subdomains. The results of numerical experiments with model data for estimating the unknown emission of a passive impurity from concentration data are presented. A comparative analysis of the results is carried out

SIMULATION OF WINTER CIRCULATION OF THE ATMOSPHERE OVER THE BAIKAL REGION

In order to assess the influence of sources of pollutants on the atmosphere of the Lake Baikal water area, the ICMMG SB RAS model is adapted to the geographical and climatic conditions of the Baikal region. Two scenario calculations describing the characteristic circulation of the winter atmosphere in conditions when Lake Baikal is covered with ice and those in the presence of an open water surface were performed. Some variants of passive impurity transfer from Irkutsk by the North-West wind flow simulated in these scenarios are discussed. With the same large-scale input data, the impurity concentrations reaching the lake's water area were lower in the scenario with frozen Lake Baikal surface. A preliminary comparison of the results of calculations has shown that the influence of differences in the thermal properties of the surface of Lake Baikal in these scenarios is manifested in the atmosphere of the surrounding territory at distances of the order of the width of the lake.

Data assimilation system for estimating methane flows using satellite data

<p>This work is devoted to the urgent task of assessing regional flows of greenhouse gases from the Earth's surface according to satellite observations. The article presents the practical and theoretical results of the first year of study in the PhD program, later they will be included in the final dissertation. Flows will be estimated based on the observational data assimilation system for a three-dimensional model of diffusive transport of gas components in the atmosphere (MOZART-4). Model for Ozone and Associated Chemical Indicators, Version 4 (MOZART-4) is an autonomous global model for the transport of chemicals in the atmosphere.</p><p>The development of a modern system for the assimilation of real satellite data for assessing greenhouse gas sources is currently a very important theoretical and practical area in science. The ensemble approach is relevant and has great potential for using both stochastic and variational methods. In the process of implementation, this is an order of magnitude simpler, since there are no cumbersome matrix calculations using the model.</p><p>To solve the problem of estimating methane flows, the parameter estimation problem was solved: an algorithm for data assimilation was developed; the Kalman filter with the transformation of the local ensemble was used as the basis for it. Using an example of a model problem, an algorithm for estimating the concentration of a passive impurity and a parameter is developed. The case was also considered when only one parameter can be estimated in the assimilation system. In this case it is considered that at the forecasting stage the parameter does not change, and the calculations in accordance with the transport model are included in the operator H, for example, as in Feng (2009,2017). H is the observation operator; transfers predicted values to observation points (and observed variables). For example, for satellite methane data, H includes:</p><ol><li>a) interpolation to the observation point;</li> <li>b) vertical averaging (using the middle core);</li> <li>c) if the observation data is obtained from a large time interval, then the operator H also includes a forecast for the model in time.</li> </ol><p>Numerical experiments were carried out with model and real data. Using numerical experiments with the model, it was shown that a large problem (global) can be solved sequentially by subregion, independently in each subregion, which allowed the use of MPI and OpenMP.</p>

Modeling coal dust dispersion from pile with protection barriers

The results of laboratory studies to evaluate the effectiveness of barriers which are used to reduce dust pollution from the coal pile are presented. The use of the Г-shaped barrier, which is set differently near the coal pile model, has been studied. A numerical model is proposed to compute coal dust concentration in the air near the pile. The Navier–Stokes equations are used to model the wind flow over the coal pile. These equations are written in the variables “vorticity-stream function”. To simulate the process of coal dust dispersion from the coal pile, the equation of convective-diffusion transfer of the passive impurity is used. For numerical integration of the modeling equations, difference schemes of splitting are used. Developed numerical model allows to perform numerical experiments taking into account the complex geometric shape of the pile and screens. The results of the computational experiments are presented.

DATA ASSIMILATION METHOD FOR THE TASK OF PASSIVE IMPURITY PROPAGATION IN THE ATMOSPHERE BASED ON A DYNAMIC-STOCHASTIC APPROACH

In this paper, we consider the method of data assimilation for the problem the propagation of the concentration a passive impurity in the atmosphere. Classical approaches to solving such problems are described, features of the application of algorithms, their minuses and pros. Two algorithms are considered: the ensemble Kalman filter and the ensemble Kalmans moother. Various ways to improve the convergence of these algorithms, such as localization and inflation factor, are considered.

On the theory of the passive impurity distribution in the turbulent air flow

The statistical model of passive impurity transfer in surface boundary layers of the turbulent atmosphere in the presence of wind is offered. Analytical expressions of the normalized concentration of impurity for arbitrary correlation tensor of the second rank of velocity pulsation when the emission source is located at a certain height over the Earth's surface are obtained. The effective coefficient of turbulent diffusion contains coefficient of molecular diffusion, longitudinal and transverse turbulent diffusion coefficients. Numerical calculations were carried out using experimental data of ground(-based) observations. The isolines describing distribution of the passive impurities at calm case are depicted at different values of a wind speed and at certain distances from a source. Dynamics of globules formation with various concentration of impurity transferred by wind is constructed. They have specific characteristic spatial scales and lifetimes.Â

Some Problems of Statistical Modeling of Intermittent Turbulent Flows and Their Solutions

Some problems of statistical modeling of turbulent flows associated with the hydrodynamic effects of intermittency of various dynamic and scalar fields are identified, and a justification of their solutions is proposed. At first examines some problems of statistical modeling of large-scale (energy-containing) turbulence structure under the conditions of turbulent and nonturbulent fluid intermittency in the turbulent flow. This primarily applies to the problem of obtaining the differential equations of hydrodynamics for conditional statistical moments (conditional averages), i.e. for single-point statistical moments of each of the intermittent media of turbulent flow. To solve this problem is given a mathematically rigorous justification of conducting the operation of conditional averaging of the Navier-Stokes equations. As a result was obtained the system of differential equations for the conditional averages of turbulent and nonturbulent fluid. The main advantage of the obtained differential equations for the conditional averages is that these equations don’t contain the source terms. Therewith is given a physical substantiation of transformation process of nonturbulent fluid in turbulent, that occurs in a thin superlayer, which separates turbulent and nonturbulent fluid. Here also is given a justification of conducting the operation of total averaging of the partial derivates, which, as it turns out, is not a permutational and leads to a number of specific features in comparison with the unconditional averaging in RANS. Another problem associated with statistical modeling of inhomogeneous turbulent flows, i.e. flows with an inhomogeneous field of scalar substance. It is known that the dynamic field with turbulent fluid does not coincide with the inhomogeneous field of scalar substance. To solve this problem is proposed a method of calculating the statistical characteristics both of the turbulent fluid and the inhomogeneous field of a passive admixture concentration. It is shown, that the conditional averages of the passive admixture concentration are significantly different. In conclusion we consider the problem of statistical modeling of diffusional turbulent combustion of not pre-mixed chemically reacting gases, expressly the modeling by the known method PDF with involving the “reduced fuel concentration” as the passive impurity concentration. To solve this problem is given a justification of new differential equations, allowing to carry out calculations only of the conditional averages for the intersection region of the dynamic field of the turbulent fluid and the inhomogeneous field of the passive impurity concentration. Some results of such calculations, performed in the self-similar field of diffusion turbulent propane plume, are presented together with the experimental data available in literature.