Gas-dynamic Processes Research Articles

Fire detection system call points types selection based on the gas and smoke environment physical parameters dynamic study in different premises

Fire detection system call points types selection is determined by the gas-smoke environment prevailing physical parameter in fire case and by this parameter change dynamic as combustion develops. Obtaining of practically important information about the gas-smoke environment prevailing parameters during a fire, their changes dynamic and the time when they reach the threshold values for call points for real objects is possible on the numerical studies results basis using the FDS program complex modeling heat and mass transfer and gas dynamic processes occurring during a fire. The performed calculations made it possible to obtain the temperature dependences, smoke optical density and carbon monoxide concentration in the near-ceiling area on time since the ignition start for a number of characteristic rooms for various purposes. The call points type choosing ambiguity for rooms with different fire load indicators is shown. The calculated data can serve as a basis for choosing the fire detection system call points types, as well as for setting up and effective functioning of multi-sensor and multi-criteria fire detectors.

Thick Cu-hBN Coatings Using Pulsed Gas Dynamic Spray Process: Coating Formation Analysis and Characterization

Thick Cu-hBN Coatings Using Pulsed Gas Dynamic Spray Process: Coating Formation Analysis and Characterization

Seyakha catastrophic blowout and explosion of gas from the permafrost in the Arctic, Yamal Peninsula

For the first time, in a channel of the Arctic river, on the Yamal Peninsula, a pingo-like feature (PLF) was revealed, where, as a result of powerful blowout, self-ignition and explosion of gas on the 28th of June 2017, the giant Seyakha Crater (C11) was formed. Expeditions in 2017, 2018 and 2019 on the C11 Crater and analysis of remote sensing data allowed to reconstruct geodynamical processes of rapid (approximately 3.5 years) growth of the PLF, caused by high gas pressure, and active thermoabrasive processes in summer seasons (speed up to 1.6 m per day), destroying the C11 Crater walls. It was discovered that before the explosion, a gas-filled thermokarst chamber (ice cavity) had existed in permafrost. Based on the use of the ground penetrating radar survey, a model of the crater and the structure of near-surface deposits was created. A previously unknown rise in the base of ground ice, probably connected with gas-dynamic process, was revealed. A scheme of distribution of frozen soil and ground ice fragments, ejected from the crater, was created and analyzed, their maximum distance from the explosion epicenter was defined as 380 m. Long-term gas emission from the crater was observed, which allowed to make a conclusion about volcanic mechanism of eruption. Large distances from deep wells to the location of the explosion (15 km and more) and determined microbial genesis of gas indicate high probability of natural origin of gas blowout and formation of the C11 Crater.

Mathematical Modeling of the Operation of an Expander-Generator Pressure Regulator in Non-Stationary Conditions of Small Gas Pressure Reduction Stations

Long-distance gas transfer requires high pressure, which has to be reduced before the gas is conveyed to the customers. This pressure reduction takes place at natural gas pressure reduction stations, where gas pressure is decreased by using gas flow energy for overcoming local resistance, represented by a throttling valve. This pressure energy can be reused, but it is difficult to implement it at small pressure reduction stations, as the values of unsteadiness significantly increase when the gas approaches consumers, whereas gas flow rate and pressure decrease. This work suggests replacing throttling valves at small pressure reduction stations for expander-generator units, based on volumetric expanders. Two implementations are proposed. A mathematical model of gas-dynamic processes, which take place in expander-generator units, was developed using math equations. With its help, a comparison was made of the stability of the operation of two possible control schemes in non-stationary conditions, and the feasibility of using an expander-generator regulator as a primary one for a small natural gas pressure reduction station was confirmed.

Coupled heat transfer in the cavity of constant volume with pulse-periodical energy supply

The possibilities of organizing a repetitively pulsed process with given frequency characteristics in a cavity of constant volume with an external energy supply to the working gas mixture are considered. Modelling of gas-dynamic and thermal processes is carried out using the numerical solution of the conjugate heat transfer problem. The gas medium is described on the basis of a viscous compressible gas model. To find the temperature field in the walls of the structure, the equation of non-stationary heat conduction is solved. The conjugation of temperature fields in a gas and a solid is carried out using an iterative procedure. In the calculations, the geometrical parameters of the cavity, the density of the energy supply, the initial pressure, and the composition of the working mixture are varied. The results of calculations obtained in the framework of the one-dimensional and two-dimensional formulation of the problem under the action of both a single pulse and a series of pulses are compared. The results obtained demonstrate the possibility of implementing the required frequency characteristics of the process for given geometric and energy parameters. Keywords: pulse-periodical energy process, gas laser, coupled heat transfer, numerical simulation, energy supply, pulse.

Сопряженный теплообмен в области постоянного объема при импульсно-периодическом подводе энергии

The possibilities of organizing a repetitively pulsed process with given frequency characteristics in a cavity of constant volume with an external energy supply to the working gas mixture are considered. Modelling of gas-dynamic and thermal processes is carried out using the numerical solution of the conjugate heat transfer problem. The gas medium is described on the basis of a viscous compressible gas model. To find the temperature field in the walls of the structure, the equation of non-stationary heat conduction is solved. The conjugation of temperature fields in a gas and a solid is carried out using an iterative procedure. In the calculations, the geometrical parameters of the cavity, the density of the energy supply, the initial pressure, and the composition of the working mixture are varied. The results of calculations obtained in the framework of the one-dimensional and two-dimensional formulation of the problem under the action of both a single pulse and a series of pulses are compared. The results obtained demonstrate the possibility of implementing the required frequency characteristics of the process for given geometric and energy parameters.

АНАЛИЗ ТЕМПЕРАТУРНО-КОНЦЕНТРАЦИОННОЙ ЗАВИСИМОСТИ ТЕРМИЧЕСКИХ ДЕФОРМАЦИЙ ФОСФОРИТОВ ПРИ НАГРЕВЕ

The work presents the results of experimental studies of thermal deformations of phosphate raw materials, which have a significant impact on the progress of chemical and energy technological processes of thermal treatment in roasting conveyor and agglomeration machines. Influence on the value of thermal deformations of chemical and mineralogical composition of phosphate raw materials supplied for processing was revealed. Parameters of thermal deformation during heating are determined taking into account heating rate. It has been found that thermal deformations in the region of high temperatures contribute to softening and melting of phosphate materials, thereby contributing to negative gas dynamics processes in the dense layer of phosphorite pellets on the sintering machine conveyor or in the sintering layer on the agglomeration machine belt

ЧИСЛЕННОЕ МОДЕЛИРОВАНИЕ ПРОЦЕССОВ ВЗАИМОВЛИЯНИЯ ВОЛНЫ ГАЗА И ДЕФОРМИРОВАННОЙ ПРЕГРАДЫ В МОДЕЛЬНОМ КАНАЛЕ АВИАЦИОННОГО ДВИГАТЕЛЯ

The aim of the study is to adapt the ANSYS CFX and ANSYS Mechanical engineering analysis systems for numerical calculations of acoustic processes in the model channels of an aircraft engine. Numerical experiments were carried out in the 2FSI (2-way Fluid-Structure Interaction Explained) formulation, which allows taking into account the interaction between the gas and the structure. A mathematical model for gas-dynamic processes is formulated, which is based on the laws of conservation of mass, momentum, energy and is closed by the equations of state of an ideal compressible gas and turbulence. A mathemati-cal model is formulated for estimating the stress-strain state of a structure, taking into account the movement of the partition in the framework of the linear theory of elasticity. Boundary conditions are determined. The task of the study was to evaluate the influence of the choice of the type of partition material on the propagation of a sound wave along the flow to the partition and beyond. As a partition, materials were chosen that differ in the value of the modulus of elasticity and Poisson's ratio, steel, tita-nium and polyethylene. Graphical dependences of the pressure amplitude at six control points are obtained. Graphs of moving partitions depending on the type of material are obtained. Computational experiments were carried out at Perm National Re-search Polytechnic University using the computing resources of the cluster of the Center for High-Performance Computing Sys-tems.

ERFWHG CHANGE IN THE PULSE-POWER CHARACTERISTICS OF THE ENGINE WORKING WITH THE CYLINDER DISCONNECTING IN IDLE MODE

The parameters of gas-dynamic processes in the engine cylinders affect the forces on the supports. By evaluating the impulse actions and peak values of the forces on the supports, it is possible to evaluate the efficiency of each cylinder. (Research purpose) The research purpose is studying the process of changing the external impulse-power characteristics of an internal combustion engine operating in idle mode with some disconnected cylinders. (Materials and methods) The article presents a methodology for quantifying the impulse effect of the engine on the supports during the combustion cycle and expansion of each cylinder and experimental studies on a diesel four-cylinder four-stroke engine D-243. During the research, the fuel supply to one, two and three cylinders was gradually turned off and the forces arising in the supports were recorded using strain sensors and a set of measuring equipment. (Results and discussion) With uniform engine operation with a minimum crankshaft rotation speed in idle mode, the peak values of the forces on the supports during the combustion and expansion cycles reached an average value of 200 newtons, the magnitude of their impulse action takes an average value of 8.2 kilonewtons-seconds equal for all cylinders. With the gradual shutdown of the cylinders, the peak values of the forces on the supports at the combustion and expansion stroke increase to 910 newtons when working with only one cylinder, and the average value of the force pulse is 50 kilonewtons-seconds. The depressurization of non-working cylinders increases the peak force effect of the working engine cylinder on the supports to 1200 newtons, and the pulsed force effect up to 85 kilonewtons-seconds. (Conclusions) The proposed methodology for evaluating the parameters of the gas-dynamic processes of the engine based on the external pulse-power characteristics will allow to quickly assess the technical condition and efficiency of each cylinder and the engine as a whole.

Strength and Service Life of a Steam Turbine Stop and Control Valve Body

The stability of operation of steam turbines depends (along with other factors) on the reliable operation of their steam distribution systems, which are based on stop and control valves. This paper considers the strength of the elements of the K-325-23.5 steam turbine valves, in whose bodies, after 30 thousand hours of operation, cracks came to be observed. Previously determined were the nature of gas-dynamic processes in the flow paths of the valves and the temperature state of the valve body in the main stationary modes of operation. To do this, a combined problem of steam flow and thermal conductivity in stop and control valves was solved in a three-dimensional formulation by the finite element method. Different positions of the valve elements were considered taking into account the filter sieve. The assessment of the thermal stress state of the valve body showed that the maximum stresses in different operating modes do not exceed the yield strength. Therefore, the assessment of the creep of the valve body material is important to determine the valve body damage and service life. Modeling the creep of the stop and control valves of the turbine was performed on the basis of three-dimensional models, using the theory of hardening, with the components of unstable and steady creep strains taken into account. The creep was determined at the maximum power of the turbine for all the stationary operating modes. The maximum calculated values of creep strains are concentrated in the valve body branch pipes before the control valves and in the steam inlet chamber, where in practice fatigue defects are observed. However, even for 300 thousand hours of operation of the turbine (with a conditional maximum power) in stationary modes, creep strains do not exceed admissible values. The damage and service life of the valve bodies were assessed by two methods developed at A. Pidhornyi Institute of Mechanical Engineering Problems of the NAS of Ukraine (2011), and I. Polzunov Scientific and Design Association on Research and Design of Power Equipment. (NPO CKTI) – 1986. The results of assessing the damage and the turbine valve body wear from the effects of cyclic loading and creep of the turbine in stationary modes for 40, 200 and 300 thousand hours show that the thermal conditions of the body in the steam inlet chamber are not violated (without taking into account possible body defects after manufacture). The damage in valve body branch pipes after 300 thousand hours of operation exceeds the admissible value, with account taken of the safety margin. At the same time, the damage from creep in stationary operating modes is about 70% of the total damage. The maximum values of damage are observed in the areas of the body where there are defects during the operation of the turbine steam distribution system. The difference between the results of both methods in relation to their average value is ~20%.

Influence of valve effect on energy efficiency of layer gasdynamic systems

The direction of gas movement and the properties of the granular layer, which must be taken into account in the Darcy-Weisbach formula, have a significant effect on the energy efficiency of gas-dynamic processes in layered systems. The complex form of the regularity of the coefficient of resistance from the content of fine fractions in the layer is justified by the wavy shape of the channels in which the fine fractions are located. However, this phenomenon can be justified by the forced migration of small particles inside the cavities of the layer under the influence of mobile gases. The influence of the mobility of particles during air blowing of separated and mixed granular layers on the coefficient of gas-dynamic resistance is investigated. A smooth decrease in the value of the coefficient with an increase in the air flow rate before the transition of the layer to the fluidization mode was observed for monofraction layers. Fractures, caused by the formation of a low-permeability area due to the placement of small fractions in narrow places between large ones, have been identified for the separated layers. The presence of such a fracture depends on the ratio of particle sizes and their roughness. The increase in pressure under the bed allows the fines to gradually move upward through the voids between the larger fractions. A layer of small balls formed on top and the pressure loss in the entire steel layer is about twice as high as for the separated layer. This is due to the fact that the small balls completely fill the voids between the large pellets and the total height of the column of balls in the channels of the layer has approximately doubled in relation to the initial filling height. In addition, the tortuosity of the channels between large pellets, through which air passes, increases, which contributes to an increase in the gas-dynamic resistance to the layer. An abrupt transition to a "fluidized" bed is observed for a monofractional charge of small balls at a critical gas pressure drop, pressure pulsations occur ±100 Pа and consumption ±0,365·10–3 m3/s. A spontaneous sharp drop in the drop occurs after the formation of geyser channels. The rigid structure of the layer, characteristic of the agglomeration process, ensures uniform movement of gases in the layer, but the valve effect occurs when the content of fine fractions in the layer is more than 3.1 % and increases the energy consumption for the movement of gases in the layer by 30 %. The placement of two or more particles in such cavities between large and retained in them due to friction forces occurs in this case. Elimination of the low-permeability barrier will increase the height of the dormant layer from 400 to 550–600 mm and reduce the consumption of solid fuel of the charge by 10–15 % due to its redistribution along the height.

Continental shale gas dynamic enrichment and evolution over geological time

Shale gas content alters with geological time, which indicates that its formation has evolved and is dynamically enriched. In this paper, a numerical model is proposed to describe the dynamic enrichment and evolution process of shale gas over geological time. The model involves the coupled process of geological conditions (temperature and pressure), source rock quality (abundance, type and maturity), and reservoir characteristics (mineral composition and pore characteristics). By comprehensively considering the gas occurrence state, pore water content and overpressure, we divide the shale gas dynamic evolution process into six stages: dissolved gas stage, adsorbed gas stage, free gas stage, overpressure formation stage, overpressure maintenance stage, and overpressure reduction stage. As a case study of continental shale gas from the Shahezi Formation in the Xujiaweizi Fault Depression, the dissolved and adsorbed gas stages are of less significance to shale gas accumulation, despite their long life. In contrast, the free gas and overpressure formation stages with short geological times are of decisive significance for the efficient accumulation of shale gas, whereas the overpressure maintenance and reduction stage are of great significance to shale gas preservation. Moreover, the gas-in-place content simulated by this method is close to the estimated value of the process analysis method, which is higher than that estimated by the United States Bureau of Mine method and lower than that estimated by the Amoco curve fitting method.

Application of the Riemann problem with complex equations of state for modeling three-dimensional flows of real media

The paper considers the numerical simulation of spatial flows of real media in safety valves on the basis of the problem of an arbitrary discontinuity breakdown with complex equations of state. The solution is constructed by means of the developed numerical method, which is a modification of the classical scheme by S. K. Godunov and includes various complex equations of state of matter. The Van der Waals equations of state were used to model the flow of real gases, and the Mie-Grüneisen equation was used to describe the flow of a real weakly compressible fluid. It is shown that the proposed numerical schemes allow for modeling fluid and gas dynamic processes in real fluids and gases with shock waves and contact discontinuities and can be used both in areas of classical medium behavior and in areas with non-classical behavior.

Числове дослідження змішування в системі генерації газової суміші

The subject of research is a gas-dynamic process of mixture formation with a given component mass fraction during overflow through the mixer nozzles in the mixture generation system. The aim of the study is the scientific and experimental evaluation of the mixer technical solutions to ensure the accuracy and homogeneity of the gas mixture. The current work conducts numerical study on the flow of a gas flow through the mixer nozzles of the mixture generation system, ensuring its stoichiometric component composition and homogeneity. The problem is solved by developing adequate mathematical models of gas-dynamic flow and analyzing the results of numerical simulations. The following results were obtained. A mixer with the nozzles in the mixture generation system has been created and a technical solution for its design has been scientifically substantiated. The areas of flow sections of mixer nozzles are experimentally established. A mathematical model of generating a mixture with a given component mass fraction was developed and a series of numerical experiments was conducted to study its overflow through the mixer. A 3D simulation was conducted using ANSYS CFX software. The stationary formulation of the problem is applied. In the nozzles of closed overflow of the mixer, the heat exchange of the gas flow with the walls is taken into account by solving a separate problem and determining the corresponding heat transfer coefficients. At the inputs to the mixer, the ratio of the initial pressure of the components of the mixture is determined, which ensures its stoichiometric composition. The fields of the gas flow velocities, the mass flow rate of the components of the gas mixture through the mixer, and pressure and temperature fields are obtained. Based on the simulation results, it was found that the design of the developed mixer ensures the creation of a gas mixture with a homogeneity of at least 3%. With a constant pressure ratio of the mixture components to the mixer inlet, the gas mixturedosing accuracy can be achieved at least 1%.

Oscillatory and transient flow modes in block nozzle arrangements with a base region

Multi-jet interactions are characterized by a number of shock and expansion waves, formation of turbulent shear layers and subsonic recirculation zones. The problem of the occurrence of unsteady, transient and oscillatory, processes arising in the nozzle devices of rocket engines at different flight modes is discussed. The main flow regimes, the sequence of their change and qualitative patterns of shock-wave structures that arise in each of the regimes are considered. The main emphasis is paid to the causes of occurrence and mechanisms of maintenance of low-frequency oscillations of the base pressure. The regularities of changes in the amplitude-frequency characteristics of oscillations are studied depending on the main parameters of the problem. Areas of existence of oscillatory processes are found, and a search is carried out for the ranges of design parameters, geometric characteristics of nozzle assemblies that provide a non oscillating flow of gas-dynamic processes. Hysteresis phenomena of shock-wave structure at increase or decrease in the reservoir total pressure is observed.

Flow visualization around cylinder under surface discharge action in the still atmosphere

The paper presents the universal gas-discharge system for surface discharge generation on a cylinder body providing PIV experiments and shadow studies. The system enables the flow visualization around cylinder, discharge power consumption measurements and of temperature fields on the cylindrical surface recording. Under surface discharge action on cylindrical surface in the quiescent air, the flow accompanied by the formation of a near-wall vortex structure and a set of the radially-oriented jets is visualized. The observed jets leave the thermal boundary layer and are able to influence to the gas areas located far away. The presented results indicate the effectiveness of the surface discharges use to control gas-dynamic, thermo-physical and mass transfer processes in the vicinity of streamlined bodies such as cylinders.

Spectral analysis of gas dynamic processes in the inlet system of a piston engine with turbocharger

THE PURPOSE. To carry out a comparative analysis of the spectra of gas-dynamic characteristics of flows in the intake systems of piston engines with and without turbocharging, to assess the degree of influence of the turbocharger on the flow structure in such systems, and also to propose a method for the gas-dynamic improvement of processes in the system under consideration. METHODS. Due to the complexity of the object of research, an experimental approach was taken as a basis. The experiments were carried out on a single-cylinder piston engine model, which could be equipped with a turbocharger. A system for collecting and processing experimental data based on an analog-to-digital converter was used in the study. Data on changes in local values of velocity and static pressure of pulsating flows in the intake system during the engine's operating cycle were obtained using a constant temperature hot-wire anemometer and a fast-acting pressure sensor. Spectral analysis of functions of flow velocity and pressure versus time was carried out on the basis of the fast Fourier transform algorithm.RESULTS. The article presents a comparative analysis of the spectra of the amplitudes of the velocity and pressure pulsations in the intake system of an engine with and without turbocharging. Also proposed is a method for stabilizing the pulsating flow in the intake system by installing a leveling grid in the outlet channel of the turbocharger compressor. CONCLUSION. It is shown that the installation of a turbocharger leads to a significant change in the structure of gas flows in the intake system of the engine. It has been established that the presence of a leveling grid in the intake system of a turbocharged piston engine leads to a decrease in the low-frequency amplitudes of the flow velocity and pressure pulsations up to 30%. It is shown that the probability of failure-free operation of an automobile engine (cylinder diameter – 82 mm, piston stroke – 71 mm) increases by almost 1% when a leveling grille is used in the intake system.

Improving the performance of the air-cooling unit in the cooling system of a radar

The article discusses the issues of reducing the size of the cooling unit of the antenna of a radar station by improving the gas-dynamic processes occurring in the air-cooling unit. The results of the experimental studies of the gas flow in a plate-fin heat exchanger, being blown by one axial fan are presented. The feasibility of changing the number of axial fans for organizing a more uniform flow around the heat-exchange surfaces has been determined by calculation and theoretical methods. The calculation results are confirmed by experimental studies of the air flow in the segment of the heat exchanger, which is provided by a smaller fan.

The Development Peculiarities of Gas-Dynamic Processes of a Pulsing Gas Flow in a Dense Layer

The Development Peculiarities of Gas-Dynamic Processes of a Pulsing Gas Flow in a Dense Layer

Mathematical modeling of a swirling jet in applications to low-emission combustion of low-grade fuels

Abstract. The search for new solutions in the field of energy, preventing negative impact on the environment, is one of the priority tasks for modern society. Natural gas occupies a stable position in the demand of the UES of Russia for fossil fuel. Biogas is a possible alternative fuel from organic waste. Biogas has an increased content of carbon dioxide, which affects the speed of flame propagation, and a lower content of methane, which reduces its heat of combustion. However, the combined combustion of natural gas and biogas, provided that the mixture of fuel and oxidizer is well mixed, can, on the one hand, reduce the maximum adiabatic temperature in the combustion chamber of power boilers at TPPs, and, on the other, increase the stability of biogas combustion. For the combined combustion of natural gas and biogas in operating power boilers, it is necessary to reconstruct the existing burners. For a high-quality reconstruction of burners capable of providing stable and low-toxic combustion of fuel, it is important to have theoretical data on the combustion effect of combustion of combinations of organic fuels on the temperature distribution in the combustion zone and on its maximum value. In this paper, self-similar solutions of the energy equation for axisymmetric motion of a liquid (gas) in a model of a viscous incompressible medium are obtained. Basing on them, a stationary temperature field in swirling jets is constructed. A set of programs based on the ANSYS Fluent software solver has been developed for modeling and researching of thermal and gas-dynamic processes in the combustion chamber. On the basis of the k - ϵ (realizable) turbulence model, the combustion process of a swirling fuel-air mixture is simulated. The results of an analytical and numerical study of the temperature and carbon dioxide distribution in the jet are presented.