Computational Gas Dynamics Research Articles

“The effect of the nozzle blade pitch on the velocity coefficient of the inflow turbine with partial blading of the runner

A numerical experiment with three groups of low-consumption inflow turbine with partial blading of the runner is considered in the paper. Geometric models of turbine stages with partial flapping of the runner with different grid spacing of the nozzle diaphragm have been developed. The object of this study is centripetal turbine stages with partial flapping of the impeller. The subject of the study is the efficiency coefficient and the velocity coefficient of the nozzles of the inflow turbine. The research method is numerical simulation of the working fluid flow using elements of computational gas dynamics. The aim of the study is to determine the effect of the nozzle blade pitch on the efficiency of the nozzle diaphragm of low-consumption inflow turbine with partial blading of the runner. The main objectives of the study are creating geometric models of turbine stages with different nozzle pitch, determining the boundary conditions of the experiment, conducting and processing the results of the experiment. The graphs of the dependence of the nozzle velocity coefficient and the efficiency of the low-consumption inflow turbine stage are provided. A comparative analysis of the nozzle velocity coefficient and the efficiency coefficient of three turbine stages with different grid spacing of the nozzle diaphragm is carried out. The velocity fields of the flow part of the turbine stages and the integral values of the parameters necessary for the three-dimensional calculation are obtained. The influence of the nozzle blade pitch on the velocity coefficient of the nozzle diaphragm and the efficiency coefficient of the turbine stage is determined. The nature and dependence of this geometric parameter on the efficiency of the study object is established, conclusions on further improvement of turbine stages with partial blading of the runner are made.

Актуализация руководств по безопасности в области оценки риска аварий на производственных объектах

Changes in the legislation in the field of industrial safety, as well as the experience of declaring industrial safety, developing safety cases for hazardous production facilities and other work related to risk analysis (assessment), required introduction of changes to the set of Rostechnadzor safety guidelines, most of which were developed in the period of 2013–2018. For this purpose, in agreement with Rosteсhnadzor, the specialists from the Group of Companies «Industrial Safety» (STC IS), STC «Industrial Safety» CJSC, ANO «Industrial Risk Research Agency», Fund of James Bruce) on a voluntary basis in the period of 2020–2022 prepared and sent to Rostechnadzor the drafts of amendments of 13 safety guides, which are currently approved. The article presents a classification of the above safety guides by content and considers a set of methods for accident risk analyses. The changes are presented in these guides related to the legal requirements for terminology, the need to make the set of safety guides more systematic. The algorithms for calculating risk indicators and affected areas were refined, the most significant of which can be distinguished: taking into account the variable clutter at the location of the fuel-air mixtures cloud, proceeding from the modern ideas about the assessment of the explosion consequences; including in the calculation of explosion parameters a model of computational gas dynamics, as well as the model designed for numerical simulation in the ejection of the jet section of the flow; actualization of the parametric models for calculating the effects of shock wave propagation in a physical explosion. The main directions are proposed concerning further improvement of the methodological support of risk analysis at the hazardous production facilities.

Влияния угла наклона сопел на коэффициент скорости центростремительной турбины с частичным облопачиванием рабочего колеса

The paper considers a numerical experiment with three groups of low-consuming inflow turbines with partial blading of the runner. Geometrical models of the turbine stages with partial blading of the runner at different angles of the nozzle inclination have been developed. The inflow turbine stages with partial blading of the runner are investigated. The efficiency and speed coefficient of the inflow turbine nozzles are calculated. There has been carried out numerical modeling of the working fluid flow by using the computational gas dynamics elements. Pick values of the nozzle apparatus velocity coefficient and the turbine stage efficiency are defined. Geometric models of the turbine stages with different nozzle inclination angles are developed, the boundary conditions of the experiment are determined, and the experiment results are analyzed and shown. There are given the dependence graphs of the nozzle velocity coefficient and the efficiency of a low-consuming inflow turbine stage. Comparative analysis of the nozzle velocity coefficient and the efficiency of three turbine stages with different inclination angles of the nozzles in the nozzle apparatus has been carried out. Conclusions are drawn about further procedures on improving the flow part of the runner to increase the efficiency of the stage.

Investigation of the stress-strain state of a turbine blade twisted according to the potential vortex law by the finite element method

Increase of power and complication of turbomachinery design is accompanied by stricter requirements to their reliability. Increasing the service life of turbomachinery is also one of the main tasks of quality improvement. Since the blade is a highly loaded element of any turbomachine, high operational requirements are imposed on it, expressed in reliability and durability of this element. A large number of factors affect the performance of the blade, one of which is its twist. The purpose of the current study is to determine the effect of twist of a gas turbine blade twisted according to the potential vortex law.The results of research of twist law influence on stress-strain state of the blade of the last stage of axial gas turbine, twisted according to the potential vortex laware presented. For this purpose, using the internal packages Ansys, CFX and Static Structural, we performed an interdisciplinary conjugate analysis of the solutions of the computational gas dynamics and static strength problems. During the analysis of the static strength problem we considered the tensile stresses arising in the field of centrifugal forces, bending stress (in different planes — from the pressure difference between inlet and outlet and from the pressure difference on the concave and convex surfaces of the blade), torsional stress, as well as thermal stress.Evaluation of the obtained results in conjunction with the analysis of previously derived analytical dependencies allowed to establish the influence of blade twist on the stress-strain state. The factor of torsion stresses and deformations should be taken into account when designing twisted blades and their subsequent gas-dynamic and strength estimation.

NUMERICAL STUDY OF THE BALANCE OF KINETIC ENERGY LOSSES IN THE FLOW PART OF A LOW-CONSUMPTION INFLOW TURBINE

The development of marine power engineering and automation, due to qualitative and quantitative changes by a significant increase in the capacity of modern power plants is considered in the paper. The object of this study is the flow part of a low-consumption inflow turbine, the subject of the study is the loss of kinetic energy in the stage of a low-consumption inflow turbine. The method of investigation is numerical simulation of gas flow using computational gas dynamics; the purpose of the study is to compare the values of kinetic energy loss coefficients in the nozzle diaphragm, impeller and output velocity losses obtained during physical and numerical experiments. The main objective of the study is to compare the values of kinetic energy loss coefficients in the turbine stage obtained during a physical experiment with the results of a numerical experiment. It is noted that low-consumption turbines are characterized by small dimensions, which do not allow to fully carrying out a physical experiment. A balance of losses of a low-consumption inflow turbine is performed in the study. A good convergence of the loss coefficients values obtained by the numerical method with the results of the physical experiment has been established. Conclusions about the possibility of applying numerical modeling for identical types of turbine stages are made.

Modification of the Redlich-Kwong-Aungier Equation of State to Determine the Main Thermodynamic Parameters in the Pure Liquid CO2 Region

The most important parameters for determining the state of real gas and the thermodynamic properties of the working fluid in a pure liquid region are pressure, specific volume, enthalpy and entropy. The paper presents a modified Redlich-Kwong-Aungier equation of state for determining pressure, specific volume, enthalpy and entropy in the pure liquid phase of real gas. CO2 was selected as the studied working fluid. When solving this problem, the author identified the main parameters of liquid carbon dioxide thermo-dynamics with the least error in comparison with experimental data in a wide range from 220 K to 300 K. It is possible to calculate pressure, specific volume, density, enthalpy and entropy of liquid CO2 with the help of the proposed method, for which the initial data are temperature, density, critical properties, molar mass and acentric factor of the working fluid. In particular, a modified Redlich-Kwong-Aungier equation is used to calculate the pressure of the working fluid. The author proposes a correlation equation of the scale correction, which is used in the Redlich-Kwong-Aungier equation for CO2 in the region of pure liquid phase. The results obtained for the pressure, enthalpy and entropy of liquid CO2 showed good agreement with the basic values, which provides the application of the proposed method in the field of pure liquid CO2, limited by the temperature range from 220 K to 300 K. The simplicity of the equation of state and the small number of empirical coefficients allows to use this method to solve practical problems of computational gas dynamics without spending a lot of time on calculations.

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The subject of the research is modern marine turbomachines which differ in many types, designs, purposes, materials and working bodies. It is noted that this diversity is guaranteed by the use of modern computer technologies from the stage of preliminary preparation of production to the release of final products. The design stage of turbine units taking into account the external characteristics of the turbine stage - power, speed, efficiency, shaft torque and others is considered. The efficiency of the stage is expressed by the efficiency coefficient, which is determined by the energy losses available in the stage. Losses, in turn, are expressed by losses in each individual element of the turbine stage design. At the same time, it is noted that the losses in the nozzle apparatus are decomposed into friction losses, edge and end losses. The object of the study is the nozzle apparatus of a low-consumption inflow turbine. The subject of the study is the velocity coefficient of the nozzle apparatus of a low-consumption inflow turbine. The research method is numerical simulation of gas flow using computational gas dynamics. The purpose of the study is to compare the value of the speed coefficient of the nozzle apparatus obtained during a physical experiment with the results of numerical modeling of the nozzle apparatus with subsonic (narrowing) channels. The conducted studies have shown that low-consumption inflow turbines are characterized by small sizes that do not allow us to fully carry out a physical experiment. A graph of the dependence of the velocity coefficient of the nozzle apparatus on the Mach number is provided in the study. A good convergence of the values of the velocity coefficient of the nozzle apparatus obtained by the numerical method with the results of the physical experiment has been established. The velocity fields of the flow part of the nozzle apparatus are obtained in the range of the Mach number ranging from 0.66 to 0.88. The possibility of using numerical modeling for this type of nozzle apparatus is concluded.

Processing and visualization of the results of parametric numerical calculations

In modern problems of mathematical modeling in computational gas dynamics, it is increasingly necessary to implement parametric studies. In these cases, the key factors of the problem under consideration vary with the chosen step within the given ranges. Calculations of this kind can be effectively carried out by constructing a generalized computational experiment. A generalized computational experiment is a computational technology that combines the solution of mathematical modeling problems, parallel technologies, and visual analytics technologies. The results of a generalized computational experiment are multidimensional arrays, where the dimension of the arrays corresponds to the number of key factors. Processing and visual presentation of such arrays requires solving a number of separate tasks. The processing and visual presentation of the results are carried out for target functionals represented as a function of many variables. The report presents an examples of solving specific processing and visualization problems based on the implemented generalized computational experiment for 3D cone in supersonic flow.

Application of computational gas dynamics methods for calculating losses during rotation of solids in low vacuum conditions

On the basis of a mathematical model with distributed parameters, a method for determining aerodynamic losses during high-frequency rotation of a flywheel accumulator is developed. The power of losses due to friction of the rotor against the air is determined as a function of the pressure in the chamber. A comparative analysis of the aerodynamic losses under low vacuum conditions at various pressures of the working medium and the data obtained on the basis of empirical dependences and presented in the scientific literature on this topic is carried out. The maximum difference between the loss power values is no more than 25%. The data deviation decreases as the pressure in the chamber decreases.

Уточнение характеристик аэродинамического сопротивления движению специальных колесных шасси и тягачей на основе применения методов вычислительной газодинамики

An accurate assessment of the characteristics of the aerodynamic resistance to movement is important for the preliminary selection of the parameters of the engine, transmission and chassis of a special wheeled chassis or tractor. The strength of the movement resistance affects the dynamic characteristics of the car. The existing calculation methods allow for a wide variation of the aerodynamic drag coefficient, which complicates the task of preliminary selection of car parameters. The purpose of this article is to clarify and develop the engineering methodology for carrying out traction-dynamic calculations of special wheeled vehicles and tractors based on the results of computer modeling performed using computational fluid and gas dynamics (CFD modeling) methods. The modeling methodology and calculation results of a special wheeled chassis manufactured by JSC «BAZ» are considered.

Solution of super- and hypersonic gas dynamic problems with a model of high-temperature air

The study considers the solution of a number of problems of supersonic and hypersonic gas dynamics using a model that takes into account the dissociation and ionization of air. The results of verification and validation of the developed numerical method using various difference schemes (the Roe scheme, Rusanov scheme, AUSM scheme) for discretizing convective flows are presented. The formulation of the mathematical model for high-temperature air uses the presence of equilibrium chemical reactions of dissociation and ionization. For this purpose, at high incoming flow velocities, the Kraiko model is applied, which includes equilibrium chemical reactions in air at high temperatures. To discretize the basic equations, the finite volume method on an unstructured grid is applied. One of the features of the constructed mathematical model is the implementation of the transition between physical and conservative variables. Relationships are given, with the help of which the transition from conservative variables to physical ones and vice versa is carried out when using the high-temperature air model. To ensure the stability of numerical calculations, an entropy correction is introduced. The decrease in entropy in the solution of hyperbolic equations is excluded by introducing an artificial viscosity according to Neumann, as well as by using the Godunov method with an exact solution of the Riemann problem and methods based on the approximate solution of the problem of the decay of an arbitrary discontinuity. A number of problems of supersonic gas dynamics (supersonic flow in a channel with a straight step and supersonic flow around a sphere) are numerically solved taking into account high-temperature effects. The criteria for the accuracy of numerical calculations related to the location of shock-wave structures are discussed. The calculated shock-wave structure of the flow is compared with the data available in the literature, as well as with calculations using the perfect gas model. Some results of numerical calculations are compared with the available experimental data. The shock-wave flow patterns obtained in the framework of the inviscid model, which takes into account the effect of viscosity and its dependence on temperature, and the turbulent flow model are compared. On the basis of numerical simulation data, the influence of viscous effects on the flow characteristics in a channel with a straight step and hypersonic flow around a sphere is considered. The influence of various numerical factors on the shape of the bow shock and the presence of fluctuations in the solution behind the shock is emphasized. As part of the work, a computational module was prepared for the commercial package Ansys Fluent, implemented with the help of user programming tools. The prepared module expands the standard capabilities of commercial software focused on solving computational gas dynamics problems, and is available to Ansys Fluent users for solving hypersonic aerodynamics problems. The developed means of numerical simulation can be useful in the design and optimization of hypersonic aircraft.

МОДЕЛЮВАННЯ ТА ОПТИМІЗАЦІЯ ПРОЦЕСУ ОЧИЩЕННЯ ПОВІТРЯ ВІД ЗЕРНОВОГО ПИЛУ ЗАСОБАМИ ОБЧИСЛЮВАЛЬНОЇ ГІДРОГАЗОДИНАМІКИ

The article is dedicated to the development of generalized methods of calculation, modeling and optimization of the cyclones’ parameters that are used to clean the air from the grain dust. The basis of the developed methods is the usage of computational hydraulic gas dynamics, in particular the SOLIDWORKS software package and the integrated CFD-package SOLIDWORKS Flow Simulation, as well as the principles of theory of similarity and dimensions. The deposition efficiency coefficient was chosen as the optimization criterion that can be calculated as the ratio of the mass of deposited particles to the total mass of grain dust particles entering the working volume of the cyclone. By means of SOLIDWORKS, a parametrized solid model of cyclone with the necessary elements of adaptation for further study of gas-dynamic processes was created. The dependence of the deposition efficiency on various parameters that can be optimized, in particular, on the pressure at the inlet and outlet nozzles of the cyclone was studied; volumetric flow rate of air to be purified; design dimensions of the working chamber of the cyclone etc. The usage of the simulation methods allowed to obtain an extended database of optimization parameters and values of the objective function that correspond to them. The generalization of the obtained data set in the form of dimensionless criteria was enabled by the analysis of the dimensions of the quantities that affect the deposition efficiency. Using the basics of similarity theory, the type of functional dependence between similarity criteria was established. The constant parameters of the mentioned power function are determined using a two-dimensional approximation using a software package for mathematical calculations – Mathcad 15. The obtained mathematical model allows to select the optimal operating modes (volumetric air flow, inlet and outlet pressures of cyclone etc.) depending on the design and the size of the cyclone that allows to maximize the efficiency of grain dust deposition.

The flow research in vane diffusers of centrifugal compressors transonic stages

. Computational fluid and gas dynamics methods are used at all stages of design, including blade machine design: from the creation of a schematic design to a detailed study of all the main units [1, 2]. The industries using refrigeration centrifugal compressors (oil refining, chemical, food) development requires the machines unit capacity, efficiency and reliability increase, the weight and size characteristics and metal consumption decrease. Since this machine type production often has a small-scale or individual character, and the needs for machine specified characteristics maintain during the entire service life exists, design remains an important stage in the creation process. This article is devoted to the possibility of validating the calculations using the numerical gas dynamics methods research. The centrifugal compressor end stage numerical and a full-scale research were made during the investigation; refrigeration centrifugal compressor end stage full-scale investigation carried out by D.A. Kapelkin was chosen as a base of the research [3]. As a result, the diffuser flow numerical simulation results were analyzed and the calculated and full-scale characteristics comparison was carried out. Recommendations for the numerical gas dynamics methods application are given in a particular case, applied to refrigeration centrifugal compressors vane diffusers gas-dynamic calculations.

Моделирование влияния процессов рассеяния на силу излучения высокотемпературной струи методом Монте-Карло

The purpose of the paper was to study the scattering effect in the gas jet model on the angular dependence of the radiation intensity. Along with the Monte Carlo method used as the main calculation method, we applied a direct numerical solution of the equation of radiation transfer in a non-scattering medium, known as the discrete directions method, or Ray-Tracing Method. We compared the results obtained using the two methods when calculating a non-scattering medium in order to verify the solution according to the Monte Carlo scheme. Furthermore, we calculated the medium with an increasing value of the local scattering coefficient. Findings of research show the significant effect of scattering processes on the redistribution of radiation energy from the surface of the object. The computational algorithm is implemented on the CUDA C architecture. The use of analytical jet models, e.g. according to Abramovich's theory, and the results of calculations in the computational gas dynamics packages makes it possible to calculate the values of the radiation intensity for a wide class of objects

Сalculated analysis of the influence of operation and design factors on the parameters of oxygen-hydrogen low-thrust rocket engines

The paper presents the results of calculating thermodynamic and thermophysical properties of the combustion products of gaseous oxygen-hydrogen fuel according to the ideal LRE model taking into account the phase state of the components, as well as the parameters of a low-thrust engine according to the model of computational gas dynamics to ensure the selection of operation and design factors that define the design of a thruster for advanced aerospace objects. It is shown that ideal models can be used for the selection of some parameters, such as: the excess oxidant ratio, the pressure in the combustion chamber, the geometric degree of area expansion ratio. High-level computational gas dynamics models need to be used for the selection of some of the parameters of the engine to be designed, such as: design parameters of the propellant injection pattern, reduced length of the combustion chamber and some others. Air specific impulse was used as the selection criterion. The obtained calculation data allow one to choose the main parameters of the engine being designed with account for real processes in the combustion chamber and the nozzle of the engine.

Lagrangian visualization methods in computational gas dynamics

Lagrangian visualization methods in computational gas dynamics

Numerical studies of nozzle thrust characteristics of supersonic civil aircraft by computational gas dynamics method

Numerical studies of nozzle thrust characteristics of supersonic civil aircraft by computational gas dynamics method

The investigation of absolute flow non-uniform velocity distributions influence at the centrifugal compressor axial radial impeller inlet using numerical calculation methods in ANSYS CFX

Currently, methods of numerical modelling are widely used. They are especially widely used in the design of turbo compressors. For the specific task of designing new flowing parts of a centrifugal compressor, it is not recommended to deviate from the canonical design techniques, but it is preferable to supplement them with numerical methods. This article is devoted to the end two-element stage investigation of a centrifugal compressor with an axial radial impeller; the stage main dimensions were obtained using the method of V.F. Rice. In order to obtain the necessary pressure characteristics and determine the dependence for the absolute velocity non-uniform distribution at the inlet to the axial radial impeller, the flow path main dimensions were optimized using numerical calculation methods. The calculation was performed using the SST turbulence model using computational gas dynamics methods in the ANSYS CFX software environment. Based on the optimization results, five compressor designs and corresponding characteristics were obtained. The absolute velocity distribution nature at the inlet to the centrifugal compressor axial radial impeller for five flow path variants is investigated. Empirical dependences are obtained for the deviation of the absolute velocity at the inlet in the hub section axial radial impeller and the absolute velocity deviation at the shroud from the absolute velocity at the average diameter based on the results of a numerical experiment. Recommendations are made for further absolute velocity distributions investigating at the inlet to the compressor impeller.

Применение технологии DVM/DVMH для решения параметрических задач вычислительной газовой динамики

Применение технологии DVM/DVMH для решения параметрических задач вычислительной газовой динамики

Study of Wind Effects on Unique Buildings

The article deals with a numerical simulation of wind effects on the building of the Church of the Intercession of the Holy Virgin in the village Bulzi of the Chelyabinsk region. We presented a calculation algorithm and obtained pressure fields, velocity fields and the fields of kinetic energy of a wind stream, as well as streamlines. Computational fluid dynamic (CFD) evolved three decades ago at the interfaces of calculus mathematics and theoretical hydromechanics and has become a separate branch of science the subject of which is a numerical simulation of different fluid and gas flows as well as the solution of arising problems with the help of methods that involve computer systems.This scientific field which is of a great practical value is intensively developing. The increase in CFD-calculations is caused by the improvement of computer technologies, creation of multipurpose easy-to-use CFD-packagers that are available to a wide group of researchers and cope with various tasks. Such programs are not only competitive in comparison with physical experiments but sometimes they provide the only opportunity to answer the research questions. The following advantages of computer simulation can be pointed out:a) Reduction in time spent on design and development of a model in comparison with a real experiment (variation of boundary conditions).b) Numerical experiment allows for the simulation of conditions that are not reproducible with environmental tests (use of ideal gas as environment).c) Use of computational gas dynamics methods provides a researcher with a complete and ample information that is necessary to fully describe different processes of the experiment.d) Economic efficiency of computer calculations is more attractive than an experiment.e) Possibility to modify a computational model which ensures efficient timing (change of the sizes of wall layer cells in accordance with the chosen turbulence model).