Home – Home – Jornals – Advanced Search

This paper presents the results of an experimental study of the characteristics of a swirling flow with the formation of vortex structures in a radial burner under isothermal and reacting conditions for various flow swirling parameters. For isothermal conditions, the distributions of average and fluctuating velocity fields, including those tied to the phase of a precessing vortex, are obtained, the pressure fluctuations induced by the precessing vortex are analyzed, and the contribution of the precessing vortex structure to the overall level of turbulence is determined. The studies are carried out using modern contactless experimental methods of flow diagnostics, such as optical imaging and particle image velocimetry (PIV). An acoustic field generated by the vortex core precession (VCP) is recorded using four measuring microphones with pressure taps. The contribution of the VCP to the overall level of turbulence is revealed using the method of proper orthogonal decomposition (POD), also applied to analyze the velocity distributions obtained by the PIV method. The experiments show that, in the isothermal case, the VCP that occurs after the twist parameter overcomes a value S = 0.6 is a single-helix vortex structure, whose contribution to the overall level of kinetic turbulence energy is up to 27 %. For reacting conditions, the flame is visualized at different flow swirls and the frequency characteristics of the VCP occurring in the flow at S ≥ 0.6 are measured. It is shown that the dependence of the dimensionless frequency of the VCP as a function of the flow swrl S has the same nonmonotonic character both in the case of combustion and in the isothermal case.

Interaction of a shock wave in a gas with a combustible gas bubble of an elevated density is numerically simulated based on the Euler equations. Three qualitatively different regimes of detonation initiation are described: direct initiation of detonation in the frontal part of the bubble at sufficiently high Mach numbers of the incident wave and detonation initiation in the rear part of the bubble due to wave refraction and focusing of secondary shock waves at lower Mach numbers. It is shown that the detonation initiation regime depends to a large extent both on the shock wave intensity and on the density of the mixture in the bubble. Based on a series of computations, a diagram of initiation regimes is composed. It is demonstrated that the effect of shock wave focusing ensures successful initiation of detonation with a much lower intensity of the incident wave as compared to direct initiation.

The flow in a combustion chamber in the form of an annular gap between plates with multi-headed rotating detonation has been studied numerically. It is assumed that a homogeneous propane-air mixture with given stagnation parameters enters the combustion chamber through elementary nozzles evenly filling the outer bounding ring. The gas-dynamic parameters of the mixture are determined as functions of the stagnation parameters and static pressure in the gap. The conditions for the formation of a given number of waves in the multi-headed detonation wave related to the dimensions of the combustion chamber and parameters of the initiators are obtained. The maximum number of waves for given dimensions of the combustion chamber are established. The existence of the maximum critical number of waves in multi-headed detonation is associated with blocking of the supply of the combustible mixture. Under the considered geometrical parameters of the flow region, one to eight rotating detonation waves are formed. It is found that in the case of an uneven arrangement of initiators, there is gradual alignment of the mutual angles between the waves making up the multi-headed detonation. Calculations were performed on the Lomonosov supercomputer at the Moscow State University using an original software package implementing a modified Godunov method and one-step reaction kinetics.

A new microwave technique for measuring the gasification rate in a non-stationary mode is described. A feature of the technique is that to determine the mass loss during gasification, the time-varying resonant frequency of the microwave resonator with the sample under study is measured by sequential registration of the resonant characteristics of the sensor. This provides independence of the measurement results from the change in the quality factor of the resonator during fuel sample gasification. A sensor prototype which is a coaxial resonator in which the sample under study is placed in the region of maximum electric field was tested. Experiments have shown that the sensitivity (the ratio of the change in resonant frequency to the change in the inner diameter of the sample) of the new sensor design is two to four times higher than that of the previous sensor model.

This paper presents results of an experimental study of the processes of thermal decomposition and ignition of high-energy materials (HEMs) containing an oxidizing agent, a combustible agent, and dispersed additives of aluminum, aluminum borides (AlB₂ and AlB₁₂), and amorphous boron. A Netzsch STA 449 F3 Jupiter thermal analyzer and an experimental testbench, which includes a continuous-wave CO₂ laser, are used to investigate the response and ignition characteristics of two basic HEM compositions based on AP/SKDM/Me and PCA/AN/MPVT/Me at different heating rates. It has been established that ammonium nitrate at low heat flux densities (q < 130 W/cm²) decomposes and melts, forming a liquid layer on the reaction surface and increasing the delay time of the emergence of a HEM flame containing Al, AlB₂, and AlB₁₂. With an increase in the heat flux density, the effect of the liquid layer on the reaction surface of the sample decreases due to the rising surface temperature, the outflow rate of gaseous decomposition products, and the layer evaporation.

A conjugated physical and mathematical model for the combustion of a mixed solid fuel with the addition of polydisperse boron powder is presented. The gas-dynamic processes in a two-phase, multi-velocity, and multi-temperature heat-conducting medium, as well as heat transfer and reaction processes in solid fuel are taken into account in this model above the solid fuel surface. Boundary conditions for the equality of heat and mass flows of fuel components are set on the fuel surface. From the numerical solution of the system of equations, the dependence of the burning rate of a mixed solid fuel containing boron particles on the pressure above the fuel surface is determined.

This paper presents the results of a study of the ignition of nine brands of coal from the Kuznetsk Basin by laser pulses (120 μs and 1064 nm). Depending on the laser pulse energy density, three types of processes can be distinguished in the general process of coal ignition, and they differ in threshold, temporal, and spectral-kinetic characteristics. The first type is associated with flame ignition on the surface of coal particles, and the second and third types are related to the initiation of various thermochemical reactions within particles. The laser pulse energy density defines the intensity and duration of the flame glow, as well as the flame column height.

The detonation characteristics of an aluminized EMX with a density of ≈0.5 g/cm³ and with a mass content of aluminum up to 20 % were determined. The addition of aluminum leads to an increase in detonation velocity and detonation pressure in comparison with the parameters of the pure EMX. Replacing aluminum with ground glass leads to a decrease in both detonation velocity and pressure. The increased detonation characteristics of the aluminized EMX can be due to the partial reaction of aluminum before the Chapman-Jouguet plane. The brightness temperature of detonation products of the aluminized EMX was measured. It is shown that it decreases with the addition of aluminum to the EMX. This result demonstrates the complex effect of aluminum addition on the detonation characteristics of the EMX.

The article describes a technical approach to justification of pitwall parameters based on an integrated geomechanical research of pitwall rock mass using cores from specially drilled earth bores. The sizes of structural blocks, the rock mass quality index and structural weakness coefficient are determined. The strength characteristics of rocks and their physical properties are studied on a laboratory scale. Estimates of pitwall stability using different methods show a good agreement. The optimal pitwall parameters are recommended.

The experimental and theoretical studies show that plane deformation of granular medium induces formation of clusters with sizes of the order of 10-15 diameters of particles. The process of biaxial compression is examined. It is found that deformation has four basic modes conformable with different shapes of clusters. The modes feature a very complex alternation behavior. The process of deformation possesses memory with the Hurst exponent of 0.84. The limit loads in different modes can differ by 2 or 3 times. In problems on deformation of granular media, the calculation of mechanical condition of domains less than 80-100 diameters of particles in size should use not the continuum models but the discrete element method.