Gas-dynamic Processes Research Articles

Research of hydrodynamic processes in the flow part of a low-flow thermopressor

This research explores the hydrodynamic processes within the flow section of a low-flow thermopressor as a jet-type heat exchanger that utilizes the instantaneous evaporation of highly dispersed liquid in accelerated superheated gas flow resulting in reducing gas temperature with minimum resistance losses in contrast to conventional surface heat exchanger. The efficiency of thermopressor, as a contact heat exchanger, is highly dependent on the design of the flow section and the water injection nozzle. Geometric characteristics perform a crucial role in shaping gas-dynamic processes along the length of the thermopressor's flow section, influenced by resistance losses and local resistance in the tapering and expanding channel segments. Therefore, the optimum thermopressor design has to ensure minimize pressure losses. Using Computational Fluid Dynamics (CFD), the prototype thermopressor models were simulated and the results were compared with experimental data. The empirical equations for local resistance coefficients of thermopressor diffuser and confuser were received to evaluate the impact of various design parameters. The obtained local resistance coefficients for the confuser ranged from 0.02 to 0.08 and for the diffuser – from 0.08 to 0.32. The practical recommendations on geometric and operating parameters and characteristics for enhancing the efficiency of hydrodynamic processes in thermopressor flow part were given.

CFD Analysis of Gas-Dynamic and Heat Transfer Processes in a Propulsion System Using Polymer Fuel

In the presented work, a computer model of thermodynamic and gas-dynamic processes in a rocket engine of a new type, which uses solid polymers as fuel is considered. The design feature is the presence of a central body - a gasification chamber, where solid polymer fuel is decomposed into volatiles. To conduct the research, a preliminary thermodynamic analysis of the combustion of gasification products was carried out. Based on the results of the thermodynamic analysis using the mathematical model of the turbulent flow of viscous compressible gas, the processes of gas dynamics and heat transfer in the chamber and nozzle of the rocket engine were simulated. Analyses are made for the geometry of a real experimental sample of a polymer-fueled rocket engine developed at Oles Honchar Dnipro National University (Ukraine), which has passed the first successful tests. As a result of CFD simulation, dynamic and thermal fields in the combustion chamber and engine nozzle were obtained, and ways of further improvement of the design were determined.

Методика уточненного расчета давления в тормозных цилиндрах поезда с учетом влияния утечек сжатого воздуха, распределенных по длине тормозной магистрали

Objective: to develop a methodology for estimating the filling value of the brake cylinders of a freight train, taking into account the amount of air leakage distributed along the length of the brake line. As initial data for determining the pressure of the brake cylinders, use the pressure drop in the brake line along the length of the train, the amount of charging pressure in the head of the train and the discharge stage of the equalizing tank. Methods: experimental study of gas dynamic processes in key volumes of the braking system in the head and tail parts of the train, such as: brake line and brake cylinder. Approximation of experimental data obtained from the braking system of a real train with the derivation of generalized equations. Results: as a result of the research, refined mathematical models were obtained that allow determining the pressure in the brake cylinder of any car, as well as the average pressure in the brake cylinders along the length of the train, taking into account the amount of leakage of the charging pressure in the head of the train and the length of the train in the cars. Practical significance: The application of a new methodology for calculating the filling value of brake cylinders will allow taking into account the influence of the length of the brake line on the braking force of each train car. This will help to correct the equation of train movement and improve the accuracy of calculating the braking distance of freight trains, taking into account the technical condition of the braking network.

Time-dependent gas dynamic diffusion process in shale matrix: model development and numerical analysis

Gas diffusion is a pivotal process during shale gas recovery, which is determined by diffusion coefficient to a large extent. In previous studies, the gas diffusion coefficient is generally assumed as a constant. However, increasing experiments prove that the diffusion coefficient of shale gas is strongly time-dependent. Therefore, to perfect the theory of shale gas diffusion, this paper proposes a time-dependent diffusion model for shale gas, which incorporates time-dependent gas diffusion coefficient, composing of the bulk diffusion coefficient for free gas in organic and inorganic pores, as well as the surface diffusion coefficient for adsorbed gas in organic pores. To validate the accuracy of the new theory, we calibrate the theoretical results against experimental data, and the results show that they have strong correlation, and the time-dependent diffusion model is superior to classical model. Finally, the numerical analysis of gas dynamic diffusion process in shale matrix is conducted. The results show that at the end of diffusion, a large amounts of shale gas remain trapped in the matrix core due to the attenuation of gas diffusion coefficient. In addition, neglecting the time-dependent nature of gas diffusion in shale matrix leads to a significant overestimation of gas production.

Про фундаментальну підготовку фахівців авіаційної та аерокосмічної галузей

The subject of the study is the state of the fundamental training of specialists in aviation, rocket, and space technology. Recently, the processes of expanding and deepening the fundamental training of specialists in the specialized areas of specific higher education institutions have been intensified. Unfortunately, experience of recent years has shown, the priorities rightfully belong to the aviation and aerospace industries, both in the scientific/creative and design/production spheres. Training of the specialists in the field of aerohydrodynamics of aircraft and their components; gas dynamics of the modern aircraft engines of various types, is currently the priority. In addition, both – the problems in aeroelasticity and research in the field of aerodynamic acoustics related to the environmental safety of the operation of aviation equipment are important for the design of the modern aircraft. Moreover, the design of aircraft that overcomes trans- and supersonic flight speed, requires in-depth study of the processes of heat and mass exchange determining physico-chemical transformations, which are also present in the internal gas-dynamic processes of gas-turbodynamic and rocket engines of aircraft. Structure and comparative analysis study of programs and courses for fundamental training of specialists in the aerospace industry at the universities of USA, Canada, Germany, China, as well as in KhAI, Ukraine, are presented. This study provides comparative information about scientific and experimental bases of aerodynamic complexes available in Ukraine and in leading organizations of North America and Western Europe. This study demonstrates the real unification of deep fundamental theoretical knowledge and practical skills with experimental research based on existing modern research laboratories. Conclusion. Analysis and comparative indicators presented in paper allow us to state that based on today’s needs, the National Aerospace University "Kharkiv Aviation Institute" is capable of significant increase of the quality of training for specialists of all levels for the developed aviation and rocket-space industries of Ukraine.

Взаимосвязь окружной скорости и потерь энергии в проточной части центростремительной турбины с частичным облопачиванием рабочего колеса

Low-consumption turbomachines are devices that play an important role in the drive of various units in the field of shipbuilding, aircraft engineering and other branches of heavy engineering. They have some advantages over a high-average power turbine. The largest number of low-consumption turbomachines are made partial, i.e. with partial intake. The principle of a turbine with partial flapping of the impeller is considered as one of the types of partial turbomachines. The influence of the main velocity characteristic of the turbine stage on the loss of kinetic energy in the stage is investigated. The simulation of gas dynamic processes occurring in the turbine stage was carried out using the ANSYS Workbench software package. With the help of this complex, a three-dimensional geometric model of the turbine stage with varying degrees of impeller damping was created. By applying the finite element method, a computational grid, a computational model are generated, and boundary conditions of a numerical experiment are set. The result of the numerical experiment is graphs of the dependence of kinetic energy loss on the circumferential velocity (speed characteristics of the turbine stage). This dependence can be represented not only graphically, but also with the help of mathematical apparatus. An example of such an apparatus is the polynomial dependence. The considered mathematical design can be used in order to optimize mathematical models of gas flow in the flow part of a low-flow turbine. Cubic two-parameter polynomials of kinetic energy losses in the flow part of the nozzle and impeller are obtained, and an assessment of its applicability in the current mathematical model is given.

Multi-mode Optimization of Diesel Engine Turbocharging

The thermogasdynamic engine system consisting of a number of subsystems of varying complexity is considered. The solution to the optimization problem in general is carried out by a multi-step iterative process of exchanging information between the levels repeatedly with refinement for all successive iterations of the initial data. Mathematical models of gas-dynamic processes in the flow section in variable modes, the simulation model of a gas turbine engine, and the model of multi-mode optimization of a gas turbine engine have been developed. The optimization of general-mode parameters is carried out in the space of points each of which reaches a minimum expression for the mode parameters.

Modelling of gas-dynamic processes in the design of small-sized installation for the production of micro-powders by gas spraying melt quenching in a horizontal reactor.

A new scheme for obtaining metal powders by gas spraying is present. The atomization takes place in a horizontal reactor where the interacting flows of the melt and the atomizing gas are perpendicular. The theoretical calculations performed within the selected approximation, quantitative values of process parameters, describing the interaction of flows were obtained as a result. The penetration depth of the gas stream into the melt jet at different pressures and gas flow rates was appreciated. The liquid melt jet, in initial approximation, as a flow of non-reactive particles of a spherical shape with a diameter in the range 40-250 μm in order to evaluate the selected parameters of the design of the spray chamber (atomizer) was considered. A relationship between the distribution of gas flow velocities and the distribution of the velocities of condensed particles in the atomizer chamber was modelled. We have found the areas of the atomizer in which the “reverse” flow of light particles (with a diameter of less than 80 μm). The vortex motion of the gas in the chamber induces this effect. We have found and modeled the correlation between the distribution of gas flow velocities and the distribution of the velocities of condensed particles in the atomizer chamber. The simulation results show that the investigated range of gas-dynamic characteristics in the sprayer of the chosen design ensures the production of powder materials of a given dispersion.

Stochastic Modeling of Star Formation Histories. III. Constraints from Physically Motivated Gaussian Processes

Galaxy formation and evolution involve a variety of effectively stochastic processes that operate over different timescales. The extended regulator model provides an analytic framework for the resulting variability (or “burstiness”) in galaxy-wide star formation due to these processes. It does this by relating the variability in Fourier space to the effective timescales of stochastic gas inflow, equilibrium, and dynamical processes influencing giant molecular clouds' creation and destruction using the power spectral density (PSD) formalism. We use the connection between the PSD and autocovariance function for general stochastic processes to reformulate this model as an autocovariance function, which we use to model variability in galaxy star formation histories (SFHs) using physically motivated Gaussian processes in log star formation rate (SFR) space. Using stellar population synthesis models, we then explore how changes in model stochasticity can affect spectral signatures across galaxy populations with properties similar to the Milky Way and present-day dwarfs, as well as at higher redshifts. We find that, even at fixed scatter, perturbations to the stochasticity model (changing timescales vs. overall variability) leave unique spectral signatures across both idealized and more realistic galaxy populations. Distributions of spectral features including Hα and UV-based SFR indicators, Hδ and Ca H and K absorption-line strengths, D n (4000), and broadband colors provide testable predictions for galaxy populations from present and upcoming surveys with the Hubble Space Telescope, James Webb Space Telescope, and Nancy Grace Roman Space Telescope. The Gaussian process SFH framework provides a fast, flexible implementation of physical covariance models for the next generation of spectral energy distribution modeling tools. Code to reproduce our results can be found at https://github.com/kartheikiyer/GP-SFH.

Экспериментальное исследование работы пневматических тормозов грузового подвижного состава при однотрубном и двухтрубном питании

The article demonstrates the results of the study of the pneumatic processes of standard and upgraded rolling stock braking systems. The purpose of the study was to identify the shortcomings of the classical pneumatic braking system that affect the current level of safety and speed of freight trains, as well as the possibility of eliminating them by upgrading the existing braking system using a two-tube power supply. Based on the data obtained from the study of the upgraded braking system performed in laboratory conditions, as well as data obtained from experiments conducted on trains, graphs of the dependence of the compressed air pressure of the brake line, brake cylinders and feed line on time for the new braking system are compiled. According to the results of the performed studies, it was concluded that the standard braking system has a number of disadvantages associated with the speed of gas dynamic processes and the uneven distribution of pressure in the brake cylinders along the length of the train. The study found that the two-tube braking system will increase the speed and safety of trains.

Моделирование участка газотранспортной системы в среде Simulink

The article discusses the possibility of modeling a section of a gas transportation system in the Simulink environment in order to develop approaches for managing the balance of incoming and outgoing flows. The model consists of gas elements such as a controlled reservoir, a pipeline, a flow sensor, a pressure and temperature sensor, gas properties, and a solver. Testing of the model showed its adequacy to physical gasdynamic processes. The use of the model will make it possible to generate data, train neural networks, identify and classify deviations in real data, and make decisions on predictive maintenance, aimed at increasing the efficiency of managing the gas transportation system as a whole.

Assessment of the influence of fuel system elements on the filling coefficient of a gas engine

The purpose of this work is to determine the dependence of the filling factor on the position and burial of the gas supply tube in the inlet manifold of the gas engine. Modeling of gas-dynamic processes occurring during engine intake was carried out by finite element method in the Ansys Fluent engineering analysis software environment. As geometric models for modeling, the part of the engine intake system in which the gas fuel supply tubes were located, which were located in different parts of the intake manifold and had a different amount of burial into the air flow, was considered. Simulations have shown that gas inlet tubes are the source of significant hydraulic losses in the engine inlet system, and as the amount of pipe buria into the inlet manifold cavity increases, these losses increase. Keywords filling ratio, engine intake process modeling, gas engine, hydraulic losses, gas supply elements, intake manifold

Plasma-Chemical Disposal of Silicon and Germanium Tetrachlorides Waste by Hydrogen Reduction

The processes of hydrogen reduction of silicon and germanium chlorides under the conditions of high-frequency (40.68 MHz) counteracted arc discharge stabilized between two rod electrodes are investigated. The main gas-phase and solid products of plasma-chemical transformations are determined. Thermodynamic analysis of SiCl4 + H2 and GeCl4 + H2 systems for optimal process parameters was carried out. Using the example of hydrogen reduction of SiCl4 by the method of numerical modeling, gas-dynamic and thermal processes for this type of discharge are investigated. The impurity composition of gas-phase and solid reaction products is investigated. The possibility of single-stage production of high-purity Si and Ge mainly in the form of compact ingots, as well as high-purity chlorosilanes and trichlorogermane, is shown.

Comparative numerical analysis of electromagnetic forces in DC and HFPC TIG welding

The paper presents a detailed theoretical analysis of the electromagnetic forces in the arc plasma and the weld pool metal in Tungsten Inert Gas (TIG) welding at direct current (DC) and high-frequency pulse current (HFPC) modulation with a frequency of 10 kHz. The electromagnetic (Lorentz) force, acting on arc plasma and metal is presented via potential (magnetic pressure) and rotational (equivalent electromagnetic force) force components. This approach allows us to substantially simplify the analysis of the Lorentz force effect on the arc plasma and weld pool metal under different arc burning modes. It was shown that in HFPC TIG welding with a given frequency, the effect of modulated current on the arc plasma is inherently non-stationary, whereas the effect on the weld pool metal is determined by the time-averaged magnitude of electromagnetic force throughout the period of current modulation. The proposed approach serves as a basis for numerical analysis of the electromagnetic forces in arc plasma and weld pool metal during DC and HFPC modes of the welding process. We established that the application of HFPC modulation promotes a greater intensity of both the gas-dynamic processes in the welding arc, thereby significantly increasing the pressure on the weld pool surface, and convective heat transfer from the most heated central region near the weld pool surface towards the weld pool bottom. Both these factors lead to an increase of the arc penetrability in the case of the HFPC mode compared with the DC mode, all other conditions being equal.

Physical simulation aspects of structural changes in rock samples under thermobaric conditions at great depths

When designing the parameters for the development of oil and gas field at significant depths, crucial to comprehend how certain factors affect the behavior of reservoir rocks and host rocks. These factors include the high level of rock stress, the ambient temperature field, and the hydro- and gas-dynamic processes within the mass. The impact of one or a combination of these factors can result in alterations to the construction, structure, composition, and properties of the rock mass and, ultimately leading to a mismatch between the design solutions and the actual conditions.The purpose of the research is to establish a methodology for conducting laboratory studies that investigate the impact of the mode of occurrence of oil and gas field reservoirs at great depths on the properties of rock samples.The research objectives encompass a theoretical analysis and the identification of the principal factors influencing rock behavior and changes in internal structure. Additionally, the objectives include developing laboratory research methods that comprehensively simulate these factors and conducting trial experiments to assess their effects.As part of the project, tests were conducted on sandstone samples collected from depth ranging from 3.5 to 4 km within the hydrocarbon field. These studies were performed while simulating thermobaric reservoir conditions, which include temperature, rock pressure, and reservoir pressure.The results of these experiments, aimed at examining the behavior of rock samples as closely as possible to their natural reservoir occurrence at depth of 3.5–4 km, are presented. It has been observed that rock samples of the same lithology, collected from nearly identical depths, can exhibit significant differences in deformation characteristics, both in the pre- and off-limit regions of loading. The findings from these studies provide the initial data for the development and refinement of geomechanical model behavior for materials that take into account not only fracture strength criteria but also dilatancy processes at various stages of rock deformation. Increasing lateral pressure within the range of 0 to to 55 MPa causes relatively minor change in ultrasonic vibration velocities, typically ranging from 1 to 10%. This makes it challenging to determine the necessity of utilizing these results for indirectly assessing changes in rock properties within the mass. Nevertheless, within the context of geophysical studies, considering variations in velocity values enhances the quality of result interpretation, especially given the substantial geometric dimensions of the rock masses under investigation.Research into the acoustic emissions of rocks in a complex stressed state enables the monitoring of spatial micro- and macrofracturing processes throughout the entire loading phase of samples. This provides a more comprehensive understanding of changes in their internal structure. The article delves into the factors that impact structural changes in oil and gas field rocks, particularly as their development extends to greater depths. The study outlines methodological approaches that facilitate the investigation of physical and mechanical properties of rock samples, while accurately modeling complex thermobaric conditions. Additionally, the it describes the technical specifications of the testing equipment, ensuring the closest possible replication of the actual conditions of reservoir rock occurrences. Lastly, the study reveals key features related to the deformation and fracture of rock samples during testing under lateral pressures of 55 MPa and pore pressures of 30 MPa, along with the creation of temperature fields up to 100 °C.

Numerical Simulation of Gas Dynamic Processes in a RFI-11/60 RF Plasmotron

Numerical Simulation of Gas Dynamic Processes in a RFI-11/60 RF Plasmotron

THREE-DIMENSIONAL BROWNFIELDS: THE TRAGEDY OF THE MINING COMMUNITIES

The processes of active restructuring in the mining industry of many countries have entailed the physical closure of enterprises, accompanied by measures to mitigate their environmental and social impacts. Brownfields that emerged in districts with developed mining industries are predominantly perceived through a stereotypically flat, superficial, and narrowly literal lens. Adhering to such an approach is risky both in terms of ecology and in the aspect of economic losses incurred in territories with concentrated localization of mines. The article provides substantiation for the importance of perceiving brownfields within a threedimensional space, with due consideration given to geological deformations, dynamics of underground water and gas flows, and the potential of gravitational and geo-thermal energy. The authors propose interpreting brownfields as either oper ating or abandoned industrial sites with buildings and infrastructure facilities on the ground surface, as well as natural landscapes that are negatively affected by geological, hydrodynamic, and gas-dynamic processes characteristic of the disturbance of the subsoil due to underground or open-pit mining operations. The reuse and recycling of industrial waste accumulated within brownfields alone cannot ensure the survival of coal-mining towns. Similarly, depopulation cannot be halted solely through economic instruments. Thus, the strategy for the development of coal-mining towns should entail ‘enlightened’ restructuring in line with the ideas of ‘Smart Shrinking’.

Исследование течения, создаваемого скользящим разрядом, с помощью методов компьютерного зрения

A quantitative study has been made of the flow with shock waves generated in air by a sliding surface discharge lasting less than one microsecond. The high-speed flow was visualized using the shadowgraph method, the process was recorded at a rate of 124 000 frames/s, the exposure time was 1 μs. The aim of this work is to study the dynamics of the two discontinuities: the cylindrical shock wave and the contact surface generated by the discharge. Each experiment allowed several hundred images to be taken of a short-lived gas-dynamic process lasting up to 1 ms. A YOLOv8 convolutional neural network was trained and used to determine the positions of the discontinuities. A data set of 984 markups was labeled. The model on the mAP50 metric achieved 0.887 and the mAP50-95 was 0.557. The model was used to automatically measure the vertical dimensions of the contact discontinuity. It expands at times up to 0.4 - 0.8 ms to a vertical size of 5 - 11 mm. The x-t plots and the velocities of the cylindrical shock waves were measured. It is shown that up to 1 ms after the discharge, the flow development is due to the blast wind motion behind the shock wave. It is shown that the use of computer vision can significantly speed up the analysis of high-speed flow visualizations and the extraction of quantitative information.

Evaluation of coal mines’ rock mass gas permeability in the equivalent stress zone

Purpose. Based on a comparative analysis of the internal mechanism of shape change of rock samples, which were loaded in specified deformations mode, and geomechanical and gas-dynamic processes in coal mass, to establish a causal link between these phenomena. To qualitatively characterise their gas permeability as a function of the rock’s volume expansion. To justify the possibility of using a full “stress-strain” diagram as a technogenic methane deposit formation model and its spatial localisation. Methodology. Theoretical research is based on using the solid mechanic constitutive principles and results of studying the rock samples failure in the mode of specified strains. Findings. The ability to use a full “stress-strain” diagram for detecting and localising methane reservoirs during the coal seams excavation was proved during the research. It was found that the compaction threshold coincides with the bearing pressure maximum in front of the longwall face. This area corresponds to the rock mass with minimal porosity and minimal filtration, which allows considering it as an envelope of an artificial gas deposit. Regularities that connect the three-dimensional equivalent stress state with the final gas permeability of the gas-saturated coal mass were obtained. These data allow creating a predictive numerical geomechanical model of methane migration paths. Originality. The ability to use a full “stress-strain” diagram in the controlled strain mode for numerical modelling of gas permeability of a methane-saturated coal mass during the mining of coal seams and the determination of technogenic gas deposit boundaries are justified. Dependences of the current and final gas permeability on the rock’s mechanical characteristics in a post-peak strain state are obtained. Practical value. Functional dependencies based on geomechanical models are obtained that allow the identification and localisation of technogenic methane reservoirs in mines during coal seam excavation, with subsequent utilisation of the extracted gas. Furthermore, methane removal enhances mining safety by reducing the risk of gas dynamic phenomena while decreasing gas emissions into the atmosphere contributes to reducing the greenhouse effect.

Modeling of the Gas Dynamic Processes with Different Equations of State

The work is devoted to the study of the features of gas-dynamic processes at the high pressures. The flows of air, hydrogen and water vapor are considered. The results obtained using the ideal gas equation and two real gas equations - van der Waals and Soave-Redlich-Kwong are analyzed. The comparison has been done on the numerical simulation results for the safety valve operation problem. The problem was solved in a three-dimensional non-stationary formulation using the finite volume method. Numerical solution method was built on the basis of the Godunov’s method. The results of a comparison of isotherms for each media are presented. Those are obtained using the considered equations of state in the regions when the gases thermodynamic parameters are changed. The influence of the gas model on the processes in the safety valve has been studied in detailsfor hydrogen. A detailed comparison of the local distributions of pressure, temperature, density, and flow velocity has been made. The complex impact of the flow parameters was studied using the integral characteristics - the gas-dynamic force acting on the disk and the gas flow rate. It has been found the gas-dynamic forces obtained within the framework of ideal gas model and the Soave-Redlich-Kwong gas are close to each other in magnitude and exceed the force for the van-der-Waals gas. However, the flow rate of ideal gas significantly exceeded that for both real gases. It is due to a twofold increase in density, which is not compensated by a decrease in the flow velocity. Thus, to obtain accurate data on the dynamic and velocity effects of gas flows on technical devices at high pressures it is necessary to use the real gas equations of state.