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This article presents the results of an analytical and computer study of the chaotic evolution of a regular velocity field generated by a large-scale harmonic forcing. The authors obtained an analytical solution for the flow stream function and its derivative quantities (velocity, vorticity, kinetic energy, enstrophy and palinstrophy). Numerical modeling of the flow evolution was carried out using the OpenFOAM software package based on incompressible model, as well as two inhouse implementations of CABARET and McCormack methods employing nearly incompressible formulation. Calculations were carried out on a sequence of nested meshes with 64², 128², 256², 512², 1024² cells for two characteristic (asymptotic) Reynolds numbers characterizing laminar and turbulent evolution of the flow, respectively. Simulations show that blow-up of the analytical solution takes place in both cases. The energy characteristics of the flow are discussed relying upon the energy curves as well as the dissipation rates. For the fine mesh, this quantity turns out to be several orders of magnitude less than its hydrodynamic (viscous) counterpart. Destruction of the regular flow structure is observed for any of the numerical methods, including at the late stages of laminar evolution, when numerically obtained distributions are close to analytics. It can be assumed that the prerequisite for the development of instability is the error accumulated during the calculation process. This error leads to unevenness in the distribution of vorticity and, as a consequence, to the variance vortex intensity and finally leads to chaotization of the flow. To study the processes of vorticity production, we used two integral vorticity-based quantities — integral enstrophy ($\zeta$) and palinstrophy $(P)$. The formulation of the problem with periodic boundary conditions allows us to establish a simple connection between these quantities. In addition, $\zeta$ can act as a measure of the eddy resolution of the numerical method, and palinstrophy determines the degree of production of small-scale vorticity.

This work is devoted to the numerical study of high-speed mixing layers of compressible flows. The problem under consideration has a wide range of applications in practical tasks and, despite its apparent simplicity, is quite complex in terms of modeling. Because in the mixing layer, as a result of the instability of the tangential discontinuity of velocities, the flow passes from laminar flow to turbulent mode. Therefore, the obtained numerical results of the considered problem strongly depend on the adequacy of the used turbulence models. In the presented work, this problem is studied based on the two-fluid approach to the problem of turbulence. This approach has arisen relatively recently and is developing quite rapidly. The main advantage of the two-fluid approach is that it leads to a closed system of equations, when, as is known, the long-standing Reynolds approach leads to an open system of equations. The paper presents the essence of the two-fluid approach for modeling a turbulent compressible medium and the methodology for numerical implementation of the proposed model. To obtain a stationary solution, the relaxation method and Prandtl boundary layer theory were applied, resulting in a simplified system of equations. In the considered problem, high-speed flows are mixed. Therefore, it is also necessary to model heat transfer, and the pressure cannot be considered constant, as is done for incompressible flows. In the numerical implementation, the convective terms in the hydrodynamic equations were approximated by the upwind scheme with the second order of accuracy in explicit form, and the diffusion terms in the right-hand sides of the equations were approximated by the central difference in implicit form. The sweep method was used to implement the obtained equations. The SIMPLE method was used to correct the velocity through the pressure. The paper investigates a two-liquid turbulence model with different initial flow turbulence intensities. The obtained numerical results showed that good agreement with the known experimental data is observed at the inlet turbulence intensity of $0.1 < I < 1 \%$. Data from known experiments, as well as the results of the $k − kL + J$ and LES models, are presented to demonstrate the effectiveness of the proposed turbulence model. It is demonstrated that the two-liquid model is as accurate as known modern models and more efficient in terms of computing resources.

A new flow modeling method on unstructured grid was proposed. As a basis system this method used quasi-hydro-dynamic equations. The finite volume method vas used for solving these equations. The Delaunay triangulation was used for constructing mesh. This proposed method was tested in modeling of incompressible flow through a channel with complex profile. The acquired results showed that the proposed method could be used in flow modeling in unstructured grid.

An approach to evaluation of a parametric portrait of integral equations of the theory of liquids in the RISM approximation was proposed. To obtain all associated solutions the continuation method was used. The equations reduced to a two-centered molecule model for symmetry reasons were deduced for molecular liquids. For molecular liquids, some equations were obtained which could be reduced, for symmetry reasons, to a two-center molecular model. To avoid critical points we changed the dependence of RISM-equations on reverse compressibility. The suggested method was used to perform numerical computations of methane reverse compressibility isotherms with three closures. No bifurcation of solutions was observed in the case of the partially linearized hypernetted chain closure. For other closures bifurcations of solutions were obtained and the model behavior nontypical for simple liquids was observed. In the case of Percus-Yevick closure nonphysical solutions were obtained at low temperature and density. Additional solution branch with a kink in the bifurcation point was obtained in the case of hypernetted chain closure at temperature above the critical point.

Efficient method for numerical solving of the steady transport equation in x-y-z-geometry has been suggested. The equation is being solved on hexagonal mesh, reflecting real structure of the reactor active zone cross-section. Method of characteristics is used, that inherits all the outcomes from the two-dimensional r-z-geometry calculation. Two variants of the method of characteristics have been applied for solving the transport equation in a cell: method of short characteristics and its conservative modification. It has been confirmed that in three-dimensional geometry conservative method has advantage over pure characteristic and it produces highly accurate solution, especially for quasi-diffusion tensor components.

The computer code NINE (Newtonian Iteration for Nonlinear Equation) for numerical solution of the boundary problems for nonlinear differential equations on the basis of continuous analogue of the Newton method (CANM) is presented. Numerov’s finite-difference appproximation is applied to provide the fourth accuracy order with respect to the discretization stepsize. Algorithms of calculating the Newtonian iterative parameter are discussed. A convergence of iteration process in dependence on choice of the iteration parameter has been studied. Results of numerical investigation of the particle-like solutions of the scalar field equation are given.

The problems of radiative-conductive heat transfer in the scattering layer are considered. They consist in finding the temperature profile and improving the heat transfer from boundaries. For their solution the Monte Carlo method is used. The different approaches of parallelization of proposed algorithm are analyzed.

This article is dedicated to numerical algorithms for solving problems of ignition and unsteady combustion of gunpowder on a uniform computational grid, and a grid with concentration near the surface of the combustion at a constant and adapts the depth under the heated layer of computational domain. The analysis of efficiency of a numerical grid.

The problem is formulated for description of objects having various natures which uses a system of linear equations with variable number exceeding the number of the equations. An important feature of this problem that substantially complicates its solving is the existing of restrictions imposed on a number of the variables. In particular, the choice of biochemical reaction aggregate that converts a preset substrate (a feedstock) into a preset product belongs to this kind of problems. In this case, unknown variables are the rates of biochemical reactions which form a vector to be determined. Components of this vector are subdivided into two groups: 1) the defined components, $\vec{y}$; 2) those dependent on the defined ones, $\vec{x}$. Possible configurations of the domain of $\vec{y}$ values permitted by restrictions imposed upon $\vec{x}$ components have been studied. It has been found that a part of restrictions may be superfluous and, therefore, unnecessary for the problem solving. Situations are analyzed when two or more $\vec{x}$ restrictions result in strict interconnections between $\vec{y}$ components. Methods of search of the basis solutions which take into account the peculiarities of this problem are described. Statement of the general problem and properties of its solutions are illustrated using a biochemical example.

In this work, we propose a method of the numerical solution of the magnetostatic problem for domains with boundaries containing corners. With the help of this numerical method, the magnetic systems of rectangular configuration were simulated with high accuracy. In particular, the calculations of some modifications of the magnetic system SP-40 used in the NIS JINR experimental installation, are presented. The basic feature of such a magnet is a rectangular aperture, hence, the area in which the boundary-value problem is solved, has a smooth border everywhere, except for a finite number of angular points in the vicinity of which the border is formed by crossing two smooth curves. In such cases the solution to the problem or derivatives of the solution can have a special feature. A behavior of the magnetic field in the vicinity of an angular point is investigated, and the configuration of the magnet was chosen numerically. The width of the area of homogeneity of the magnetic field increased from 0.5 m up to 1.0 m, i. e. twice.