No 4 (2023)

At present, numerical simulation is the main, and often the only, tool for detailed description of some physical phenomena in the study of the processes of material compression by shock waves. The study of the behavior of shock and rarefaction waves on the simplest model tests helps in the analysis of more complex calculations, for example, problems of inertial thermonuclear fusion on laser facilities. The paper considers comparative calculations of a test problem that simulates compression of a spherical layered system consisting of two substances by shock waves.

The work is devoted to the development of a new experimental method for entering controlled disturbances with a given frequency-wave structure into a supersonic boundary layer. Experimental data on the formation of disturbances from two pulsed sources (pulsed glow discharge) in the laminar flat-plate boundary layer at the Mach number equal to 2 are given. The experiments were carried out in the T-325 wind tunnel of ITAM SB RAS. The localized sources were spaced out at the same distance from the leading edge of the plate at 6 mm from each other spanwise. Flow pulsations were measured using a hot-wire probe of constant temperature anemometer, the signal was recorded synchronously with ignition of the discharges. This made it possible to distinguish the pulsations from the discharges against the background of random uncontrolled “natural” pulsations of the boundary layer. The spatial-temporal and frequency-wave structure of the generated disturbances from a single or two discharges, operating synchronously or with a time delay, are analyzed. It is found that the maximum difference in the structure of disturbances from one and two sources is observed in the central region, while at the side boundaries of the disturbances, the pulsations are close in all considered cases. In the wave spectra of disturbances from two discharges, nodes and antinodes are formed. Their position is determined by the distance between the sources and the time delay in their operation.

The structure of a steady 2D gas-droplet flow in the near-wall region behind the point of incidence of a normal or an oblique shock wave on a plane wall is investigated. In this case, the normal wave corresponds to the Mach stem in the Mach reflection mode, and the oblique wave corresponds to the regular reflection mode of the incident oblique wave. The main aim of the study is to evaluate the effect of small liquid droplets present in the free stream on the equilibrium temperature of the adiabatic wall behind the point of wave reflection. The question is investigated: to what extent the presence of an oblique shock wave incident on the wall can enhance the effect of reducing the equilibrium wall temperature by small droplets present in the flow. The flow region is split into the outer region of “effectively inviscid flow” and the region of an asymptotic laminar boundary layer. Flow calculations in each region are based on a two-fluid model of a gas-droplet mixture, taking into account the phase transition (evaporation) on the droplet surface. The most interesting wave configurations from the point of view of heat transfer, corresponding to “fully and partially dispersed waves” with incomplete evaporation of droplets behind the reflected wave, are studied. A simple limiting scheme of the formation of a liquid film by droplets deposited on the wall is adopted, with the effects of film instability and spattering being ignored. Based on numerical calculations, the estimates are obtained for the possible decrease in the equilibrium temperature of the adiabatic wall behind the point of incidence of a shock wave in a steady supersonic gas flow containing a low concentration of liquid droplets.

The distinctive features of the flow velocity and temperature fields of ascending fluid flow in a metal round pipe (round casing string installed in a production well) under the conditions of its local induction heating are studied. The results of investigation are based on numerical solution of the Navier–Stokes equations in the Boussinesq–Oberbeck approximation. The calculations were performed using the Ansys Fluent software package (license ANSYS Academic Research CFD under the agreement with the Bashkir State University dated June 15, 2020). The fluid flow rates of 10 and 50 m3 per day are considered. Such flow rates correspond to the laminar and transitional flow regimes in the casing pipe. It is found that local perturbations of the velocity and temperature fields are presented in the near-wall region of the heated casing. Fluid temperature perturbations reach several Kelvin degrees, the local flow velocity which increases due to natural thermal convection in the near-wall region of the casing string being several times higher than the cross-section-average flow velocity. The occurrence of areas of vortex flow motion over the interval of induction heating due to natural thermal convection is shown.

One of the possible mechanisms of the interaction of a bounded combustion region (flame) with an applied electric field is considered. The investigation is based on application of the electrohydrodynamics (EHD) methods to describe chemically reacting multicomponent nonequilibrium partially ionized gas mixtures. It is shown that zones of space electric charge are formed in the neighborhood of the flame boundaries under certain conditions. These zones can be affected by the electric field. The nature of modification of these zones under the influence of the electric field is investigated.

The results of an investigation of the interaction between two colliding axisymmetric laminar microjets of propane-butane mixture with and without diffusion combustion are presented. The gas mixture components flow out through round tubes at the same velocities. In the course of the experiments the lateral position of the tubes with respect to each other was varied with conservation of the angle between them. The distinctive features of the resulting jet formation are established as functions of the transverse position of the tubes. If the tubes lie in the same plane, then the resulting jet is formed in the plane orthogonal to them. This process can be observable in the case of the interaction between the jets both with and without flame. With increase in the jet outflow velocity a region of local discontinuity of the flame front is found to exist.

The heat transfer to a cylindrical water-cooled copper model was experimentally investigated in an induction VGU-4 high-frequency (HF) plasmatron of the Institute for Problems in Mechanics of the Russian Academy of Sciences. The model, 30 mm in diameter, equipped with a calorimetric transducer with a heat-adsorbing graphite surface, 13.8 mm in diameter, was exposed to the surface heating in the combined regime by nitrogen plasma and laser radiation and in the cases of the heating with only laser radiation or a nitrogen plasma jet. The experiments in the HF-plasmatron jets were performed at the pressure in the setup low-pressure chamber p = 1 × 104 Pa, nitrogen mass flow rate G = 2.4 g/s, and the plasmatron HF-generator anode power Na.p. = 22 kW. It is established that in the chosen experimental regimes the dissociated-nitrogen jet and the high-frequency induction discharge do not produce a considerable effect on the laser beam passing through them. The values of the heat flux density are obtained as functions of the laser radiation power delivered. The subsonic nitrogen plasma flow in the quartz discharge channel and in the low-pressure chamber of the VGU-4 setup is numerically modeled under the experimental conditions basing on the solution of the complete Navier–Stokes equations using the Patankar–Spalding method.