System Of Gas Dynamics Research Articles

“A posteriori” limited high order and robust schemes for transient simulations of fluid flows in gas dynamics

In this paper, we propose a novel approximation strategy for time-dependent hyperbolic systems of conservation laws for the Euler system of gas dynamics that aims to represent the dynamics of strong interacting discontinuities. The goal of our method is to allow an approximation with a high-order of accuracy in smooth regions of the flow, while ensuring robustness and a non-oscillatory behaviour in the regions of steep gradients, in particular across shocks.Following the Multidimensional Optimal Order Detection (MOOD) ([15,17]) approach, a candidate solution is computed at a next time level via a high-order accurate explicit scheme ([3,5]). A so-called detector determines if the candidate solution reveals any spurious oscillations or numerical issue and, if so, only the troubled cells are locally recomputed via a more dissipative scheme. This allows to design a family of “a posteriori” limited, robust and positivity preserving, as well as high accurate, non-oscillatory and effective scheme. Among the detecting criteria of the novel MOOD strategy, two different approaches from literature, based on the work of [15,17] and on [35], are investigated. Numerical examples in 1D and 2D, on structured and unstructured meshes, are proposed to assess the effective order of accuracy for smooth flows, the non-oscillatory behaviour on shocked flows, the robustness and positivity preservation on more extreme flows.

Численное моделирование разрушения льда газодинамической струей

When operating gas compressor stations during heavy snowfalls, uncontrolled formation of ice build-up on the filters of air-purifying devices (ACDs) can occur, which leads to accidents and downtime. Previously, it was proposed to use a gas-dynamic system for cleaning gas-permeable deformable surfaces (GPDS) to clean HEU filters. An experimental setup has been created. The paper discusses numerical modeling of ice destruction on the gas turbine engine. To destroy ice, the energy of a gas-dynamic jet is used, modeled as a short-term pulse. The study is carried out in a 3D setting, taking into account the suction flow pressure and the interaction of the deformable substrate with the ice crust. The results obtained were verified. The research is carried out using ANSYS Explicit Dynamics on the high-performance computing complex of PNRPU. The main results on the influence of a gas-dynamic jet on the cleaning ability of a gas turbine engine are presented

Shock wave solution for the planar, cylindrically, and spherically symmetric flows of non-ideal relaxing gas

In the present article, we investigate one-dimensional non-ideal relaxing gas to study solution of shocks for planar and non-planar flows, more specifically cylindrically symmetric, and spherically symmetric flows. The analytic solution of the problem is determined in the characteristic plane. It signifies that linear solution in this plane reveals non-linear behavior in the physical plane. Also, the condition of shock formation has been determined by analyzing the growth and deterioration of shocks using transport equations. It is observed that nature of the solution completely depends upon relaxing gas parameters and non-idealness. All computations are done using computational package MATHEMATICA. • Shock wave solution to the non-ideal relaxing gasdynamic system is studied. • The condition of shock formation is determined. • The growth and deterioration of shocks is discussed. • Impact of relaxing gas and non-ideal parameters on the evolution of shock is studied.

Stationary Gas Dynamics and Heat Transfer of Turbulent Flows in Straight Pipes at Different Turbulence Intensity

The gas-dynamic and heat-exchange behaviours of air flows in gas-dynamic systems have a significant impact on the efficiency and environmental performance of most technical equipment (heat engines, power plants, heat exchangers, etc.). Therefore, it is a relevant task to obtain reliable experimental data and physical laws on the influence of cross-sectional shape and initial turbulence intensity on gas dynamics and the level of heat transfer. In this study, data were experimentally obtained on the instantaneous values of the local velocity and local heat transfer coefficients of stationary air flows in straight pipes with circular, square, and triangular cross-sections at different initial values of the turbulence intensity. The measurements were carried out with a constant temperature hot-wire anemometer, thermocouples, and pressure sensors. Based on the research results, data on the turbulence intensity and averaged local heat transfer along the length of pipes with different cross-sections were summarised. It has been established that turbulence intensity in a square pipe is up to 40% higher than in a round channel; in a triangular channel, on the contrary, it is up to 28% lower. After the air flow’s initial turbulence, the relaxation of the flow in square and triangular pipes occurs faster than in a round channel. It is found that the initial intensity of turbulence leads to an increase in the averaged local heat transfer, which is typical of all investigated pipe configurations and initial conditions.

Automatic gas dynamic volumetric system for aquatic products' MA preservation

As there are many links in the cold chain logistics process, which takes a long time, the processed aquatic products are easily damaged and deteriorated. And the growth and reproduction of microorganisms in aquatic products can be inhibited by MA (Modified Atmosphere) preservation, thus extending the shelf life of aquatic products. In this context, we have developed an automatic gas dynamic volumetric system for aquatic products' MA preservation. It can control the operation platform by a 4G network cell phone client and realize remote monitoring function. Particularly, there are the main contents and conclusions of the study: 1) Combined with MA preservation, intelligent control and network communication technologies, we overcame the difficulties of remote monitoring for gas dynamic volumetric. Then, according to MA preservation and automatic gas dynamic volumetric, we designed a logical structure of the system, including the specific distribution of the sensing layer, network transmission layer and application layer. 2) We established the mathematical model for the system based on the step response method, and designed the analog acquisition, control and gas dynamic volumetric system; In addition, in this system, we realized the gas dynamic volumetric based on the embedded PID control algorithm and mass flow controller; Then, we used 4G network for remote data transmission and 4G DTU as network data transceiver, and realized remote monitoring function of mobile client through cell phone terminal applet software. 3) The results were shown by testing the stability, accuracy and communication of the system: the gas concentration error of the system floated at ± 0.25% when the gas dynamic volumetric system was stable, which was 12 times more accurate than before, and the gas dynamic volumetric speed based on embedded PID control algorithm was increasing by approximately about 50%, which greatly improved the working conditions and production efficiency.

Error Estimates of the Godunov Method for the Multidimensional Compressible Euler System

We derive a priori error estimates of the Godunov method for the multidimensional compressible Euler system of gas dynamics. To this end we apply the relative energy principle and estimate the distance between the numerical solution and the strong solution. This yields also the estimates of the L^2-norms of the errors in density, momentum and entropy. Under the assumption, that the numerical density is uniformly bounded from below by a positive constant and that the energy is uniformly bounded from above and stays positive, we obtain a convergence rate of 1/2 for the relative energy in the L^1-norm, that is to say, a convergence rate of 1/4 for the L^2-error of the numerical solution. Further, under the assumption—the total variation of the numerical solution is uniformly bounded, we obtain the first order convergence rate for the relative energy in the L^1-norm, consequently, the numerical solution converges in the L^2-norm with the convergence rate of 1/2. The numerical results presented are consistent with our theoretical analysis.

High Order Semi-implicit WENO Schemes for All-Mach Full Euler System of Gas Dynamics

In this paper, we propose high order semi-implicit schemes for the all Mach full Euler equations of gas dynamics. Material waves are treated explicitly, while acoustic waves are treated implicitly, thus avoiding severe CFL restrictions for low Mach flows. High order accuracy in time is obtained by semi-implicit temporal integrator based on the IMEX Runge-Kutta (IMEX-RK) framework. High order in space is achieved by finite difference WENO schemes with characteristic-wise reconstructions adapted to the semi-implicit IMEX-RK time discretization. The schemes are proven to be asymptotic preserving and asymptotically accurate as the Mach number vanishes. Besides, they can well capture discontinuous solutions in the compressible regime, especially for two dimensional Riemann problems. Numerical tests in one and two space dimensions will illustrate the effectiveness of the proposed schemes.

Development of equipment and technology for precision air-plasma cutting of plate steel

The authors have investigated the structure of cutting seams obtained after cutting steel 09G2S with a new narrow-jet plasma torch of PMVR-5.3 type which has a number of design features in gas dynamic stabilization system (GDS) of plasma arc. To increase the efficiency of GDS in PMVR-5.3 plasma torch, a symmetrical input of plasma-forming gas (PFG) into the flow division system and a gas-dynamic flow stabilizer using two (forming and stabilizing) swirlers with a variable number of swirl channels were used. It is shown that the achieved advantage in GDS efficiency makes it possible to obtain high cutting quality of steel 09G2S with thickness of 40 mm with high productivity and lower energy costs. Analytical methods have proved a high degree of cutting precision of the new torch– a small cut width, no melting and rounding of the upper edge, as well as a grate in the cut lower part and splashes in the cut upper part, almost zero angular deviation, minimum values of the surface microrelief and width of the thermal impact zone. Metallographic analysis and determination of hardness showed the presence of three subzones in the thermal impact zone with significant structural changes in two of them. A number of factors were noted influencing the revealed changes in the structure formation, as well as changes in the elemental composition of the cutting seam surface layer revealed during the X-ray spectral analysis. Attention is drawn to the surface microrelief after plasma cutting, which in all quality indicators is commensurate with machining of the surface after milling and corresponds to the second class of quality in terms of surface cleanliness. It was proved that the use of the new narrow-jet plasma torch allows high-quality cutting of plate steel in thickness range up to 40 mm or more. However, welding of blanks without pre-machining can be carried out with a cutting thickness of no more than 20 mm.

Initial-boundary value problem for 1D pressureless gas dynamics

The paper considers the system of pressureless gas dynamics in one space dimension. The question of solvability of the initial-boundary value problem is addressed. Using the method of generalized potentials and characteristic triangles, extended to the boundary value case, an explicit way of constructing measure-valued solutions is presented. The prescription of boundary data is shown to depend on the behavior of the generalized potentials at the boundary. We show that the constructed solution satisfies an entropy condition and it conserves mass, whereby mass may accumulate at the boundary. Conservation of momentum again depends on the behavior of the generalized boundary potentials. There is a large amount of literature where the initial value problem for the pressureless gas dynamics model has been studied. To our knowledge, this paper is the first one which considers the initial-boundary value problem.

Устойчивые методы Рунге – Кутты второго и третьего порядка для решения задач газовой динамики разрывным методом Галеркина

The Runge – Kutta methods with stability region including the circle of maximum radius are considered. The methods are used to approximate gas dynamics system of equations using the discontinuous Galerkin method. Three second-order and one third-order methods fulfiling maximum disk property are proposed and investigated. Test problems for the 1D and 2D gas dynamics are considered. The ability of the obtained methods to maintain the stability and monotonicity of the numerical solution at the maximum avaliable time steps is studied.

Solution of Riemann problem of conservation laws in van der Waals gas

The present study is concerned with the analytical solution of Riemann problem for conservation laws of van der Waals gas. By utilizing Rankine–Hugoniot conditions and Lax entropy condition, we derive classical wave solution of Riemann problem and analyze their properties. Also, it is observed here that van der Waals gasdynamics system is more complex in comparison to ideal gasdynamics case. Further, the effect of presence of intermolecular forces of attraction between the particles and variation of covolume of the gas on the density and velocity distribution across the simple wave, shock wave and contact discontinuities is discussed.

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.

Delta Shock Solution for a Generalized Zero-Pressure Gas Dynamics System with Linear Damping

Delta Shock Solution for a Generalized Zero-Pressure Gas Dynamics System with Linear Damping

On Conditions for L2-Dissipativity of an Explicit Finite-Difference Scheme for Linearized 2D and 3D Barotropic Gas Dynamics System of Equations with Regularizations

We deal with 2D and 3D barotropic gas dynamics system of equations with two viscous regularizations: so-called quasi-gas dynamics (QGD) and quasi-hydrodynamics (QHD) ones. The system is linearized on a constant solution with any velocity, and an explicit two-level in time and symmetric three-point in each spatial direction finite-difference scheme on the uniform rectangular mesh is considered for the linearized system. We study L2-dissipativity of solutions to the Cauchy problem for this scheme by the spectral method and present a criterion in the form of a matrix inequality containing symbols of symmetric matrices of convective and regularizing terms. Analyzing these inequality and matrices, we also derive explicit sufficient conditions and necessary conditions in the Courant-type form which are rather close to each other. For the QHD regularization, such conditions are derived for the first time in 2D and 3D cases, whereas, for the QGD regularization, they improve those that have recently been obtained. Explicit formulas for a scheme parameter that guarantee taking the maximal time step are given for these conditions. An important moment is a new choice of an “average” spatial mesh step ensuring the independence of the conditions from the ratios of the spatial mesh steps and, for the QGD regularization, from the Mach number as well.

Simulation of Multi-Gas Jet Flows by Use of Quasi Gas Dynamic Equation System

In the present paper, we use the quasi gas dynamic (QGD) model together with a finite volume method for the simulation of a gas jet inflowing region filled with another gas in the presence of gravity forces. A flow picture for such flow strongly depends on the gases density ratio. Numerical simulations are held for a region filled with air under atmospheric pressure. Three variants of inflowing gas are considered: methane (light gas), butane (heavy gas) and helium (extremely light gas). A difference between flow pictures for these test cases is demonstrated. Results obtained with the presence of wind in the air are also compared. Grid convergence is established by use of different spatial meshes. Here, the the QGD model demonstrated good efficiency in modeling multi-gas jet flows. The calculations were also used for the adjustment of the numerical method parameters.

Global ill-posedness for a dense set of initial data to the isentropic system of gas dynamics

In dimension n=2 and 3, we show that for any initial datum belonging to a dense subset of the energy space, there exist infinitely many global-in-time admissible weak solutions to the isentropic Euler system whenever 1<γ⩽1+2n. This result can be regarded as a compressible counterpart of the one obtained by Székelyhidi–Wiedemann (ARMA, 2012) for incompressible flows. Similarly to the incompressible result, the admissibility condition is defined in its integral form. Our result is based on a generalization of a key step of the convex integration procedure. This generalization allows, even in the compressible case, to convex integrate any smooth positive Reynolds stress. A large family of subsolutions can then be considered. These subsolutions can be generated, for instance, via regularization of any weak inviscid limit of an associated compressible Navier–Stokes system with degenerate viscosities.

Asymptotic stability of viscous contact wave for the inflow problem of the heat-conductive ideal gas without viscosity

This paper is devoted to studying the inflow problem governed by the non-viscous and heat-conductive gas dynamic system in the one-dimensional half space. We establish the unique global-in-time existence and the asymptotic stability of the viscous contact wave. The contact discontinuity in the linearly degenerate field is less stable, and the dissipative mechanism for non-viscous systems is also weaker than that of viscous systems, these all make the problem more challenging. We used the weighted energy estimates to overcome those difficulties. Some technical discussions were created carefully by taking good advantage of properties of the supersonic region and the viscous contact wave.

Thermal and mechanical improvement of the air supply system of a turbocharged piston engine

A method of thermomechanical improvement of pulsating air flows in the intake system of a turbocharged piston engine is described. The main objective of this study is to develop a method for suppressing the rate of heat transfer to improve the reliability of a piston turbocharged engine. A brief review of the literature on improving the reliability of piston engines is given. Scientific and technical results were obtained on the basis of experimental studies on a full-scale model of a piston engine. The hot-wire anemometer method was used to obtain gas-dynamic and heatexchange characteristics of gas flows. Laboratory stands and instrumentation facilities are described in the article. The data on gas dynamics and heat exchange of stationary and pulsating air flows in gas-dynamic systems of various configurations as applied to the air supply system of a turbocharged piston engine are presented. A method of thermomechanical improvement of flows in the intake system of an engine based on a honeycomb is proposed in order to stabilize the pulsating flow and suppress the intensity of heat transfer. Data were obtained on the air flow rate and the local heat transfer coefficient both in the exhaust duct of the turbocharger compressor (i.e., without a piston engine) and in the intake system of a supercharged engine. A comparative analysis of the data has been carried out. It was found that the installation of a leveling grid in the exhaust channel of a turbocharger leads to an intensification of heat transfer by an average of 9%. It was found that the presence of a leveling grid in the intake system of a piston engine causes the suppression of heat transfer within 15% in comparison with the baseline values. It is shown that the use of a modernized intake system in a diesel engine increases its probability of failure-free operation by 0.8%. The data obtained can be extended to other types and designs of air supply systems for heat engines.

Керування газовими потоками в ракетних двигунах

In the new conditions of application of launch vehicle boosters, space tugs, etc., modern rocket engines often do not satisfy the current stringent requirements. This calls for fundamental research into processes in rocket engines for improving their efficiency. In this regard, for the past 5 years, the Department of Thermogas Dynamics of Power Plants of the Institute of Technical Mechanics of the National Academy of Sciences of Ukraine and the State Space Agency of Ukraine has conducted research on gas flow control in rocket engines to improve their efficiency and functionality. Mechanisms of flow perturbation in the nozzle of a rocket engine by liquid injection and a solid obstacle were investigated. A mathematical model of supersonic flow perturbation by local liquid injection was refined, and new solutions for increasing the energy release rate of the liquid were developed. A numerical simulation of a gas flow perturbed by a solid obstacle in the nozzle of a rocket engine made it possible to verify the known (mostly experimental) results and to reveal new perturbation features. In particular, a significant increase in the efficiency of flow perturbation by an obstacle in the transonic region was shown up, and some dependences involving the distribution of the perturbed pressure on the nozzle wall, which had been considered universal, were refined. The possibility of increasing the efficiency of use of the generator gas picked downstream of the turbine of a liquid-propellant rocket engine was investigated, and the advantages of a new scheme of gas injection into the supersonic part of the nozzle, which provides both nozzle wall cooling by the generator gas and the production of lateral control forces, were substantiated. A new concept of rocket engine thrust vector control was developed: a combination of a mechanical and a gas-dynamic system. It was shown that such a thrust vector control system allows one to increase the efficiency and reliability of the space rocket stage flight control system. A new liquid-propellant rocket engine scheme was developed to control both the thrust amount and the thrust vector direction in all planes of rocket stage flight stabilization. New approaches to the process organization in auxiliary elements of rocket engines on the basis of detonation propellant combustion were developed to increase the rocket engine performance.

Influence of roughness of pipes surface on flow capacity and energy efficiency of gas pipelines operation

Long-term operation of main gas pipelines, the presence of water and mechanical impurities in the transported gas lead to erosion and corrosion damages to the inner surface of pipes, which causes an increase in its roughness. The increase in roughness results in an increase of the hydraulic resistance of natural gas pipelines, as well as affects theirs transport and energy consumption parameters. To manage the regimes of operation of main gas pipelines it is necessary to adequately predict their flow capacity and energy consumption for natural gas transportation under real values of pipe roughness which is higher than designed ones. On the basis of gas-dynamic equations of the steady-state gas movement the regularities of the influence of the pipe surface roughness on the hydraulic energy consumption of gas transportation at constant gas flow in the section of the gas pipeline are established. The regularities of the influence of the pipe surface roughness on the hydraulic efficiency coefficient of the gas pipeline section under idem difference of squares of inlet and outlet gas pressure values are clarified. It is established that the value of hydraulic efficiency coefficient of the gas pipeline section for specified value of absolute equivalent roughness of the pipe surface actually does not depend on the pipe inner diameter and slightly depends on the flowrate in the gas pipeline. The method of capacity and energy efficiency determination of the gas-dynamic system called compressor station – pipeline section for the increased pipe inner surface roughness in comparison with its designed value is proposed. The method involves mathematical modelling of gas-dynamic characteristics of centrifugal compressors, thermohydraulic calculation of the pipeline section taking into account the actual roughness of the pipe, consideration of pressure and gas flowrate technological limitations as well as energy consumption determination taken per unit of work lost in transport