Fluid Dynamics最新文献

The evolution of the regular fine structure of the colored substance distribution pattern during the spreading of a freely falling compound drop in deep water is traced for the first time using technical photo and video recording methods. The flow pattern is studied at the initial stage of the formation of the cavity and crown during the merger of a compound drop, whose core, a drop of alizarin ink solution, is covered with an oil shell. Banded structures are observed in the distribution of the colored liquid at the bottom of the cavern and the walls of the crown. The formation of banded elements of the flow pattern is associated with the influence of the processes of conversion of the available potential surface energy (APSE) during the destruction of the contact surfaces of the merging liquids. The position of the nucleus in the drop is not controlled and is determined by the formation conditions. The breakdown of the ink core into fibers is observed in all experiments in this series. The area of coverage of the surface of the cavity and the crown with the colored liquid reach a maximum at the central position of the core.

This paper is the first part of a study aimed at developing methods for the experimental and numerical modeling of jet flows with significant rarefaction effects. The experimental measurements of flow parameters in jets expanding into a vacuum or highly rarefied medium are carried out on the modern gas-dynamic complex LEMPUS-2. The electron beam diagnostic (EBD) method was used for dimensional visualization of the flows and measurements of the absolute values of the local flow density. For the numerical simulation of a stationary axisymmetric nitrogen jet expanding from a sonic nozzle into a rarefied medium, a hybrid approach is employed: gas parameters in the dense flow region are determined using the solution of the Navier–Stokes equations, and in the rarefied flow region, using direct simulation Monte Carlo. The experimental and numerical methods are compared for this problem under conditions of no condensation. The results of the numerical calculations and experiments are compared with each other and with the published theoretical data. The close agreement of the results confirms the strong predictive ability of the methods used for the outflow of a noncondensable gas from sonic nozzles into a rarefied medium.

The development and application of numerical simulation to the study of gas-dynamic processes occurring in solid-propellant rocket motors (SPRMs) is discussed. A characteristic feature of internal flows in the SPRM channels and nozzles is the presence of the condensed phase of nonspherical particles. Mathematical problems in this area feature the simultaneous occurrence of processes on many time and spatial scales, which describe the formation of agglomerate particles, their combustion, and transport in a flow of combustion products in internal channels and nozzles. A multilevel multiscale technique that combines models describing the state of the system at the micro-, meso-, and macroscales is the approach used to solve these problems. An overview of models varying in complexity and level of detail is given. The construction of multiscale models is considered in relation to the simulation of two-phase flows with metal-oxide agglomerates formed in the propellant channel and representing drops of molten metal with oxide particles attached to their surface. The options of the developed approach are demonstrated by the calculations of flows of combustion products containing agglomerate particles in the channels and nozzles of propulsion systems.

Heat exchange of silicon carbide samples in subsonic air, nitrogen and carbon dioxide plasma jets of the VGU-4 HF-plasmatron has been investigated. A significant influence of the chemical composition of the dissociated gas flow on the material behavior was revealed. The macro- and microstructure of the samples surface was analyzed, the phase composition before and after exposure was studied. The emissivity of the samples surface was investigated. Numerical modeling of the experimental modes using author’s codes based on Navier–Stokes equations was carried out. The values of the effective recombination coefficient of atoms and molecules γ_w on the material surface were obtained. Probe measurements of heat fluxes and dynamic pressures for the modes of the experiments were performed.

The interaction with the atmosphere of a meteor body or its fragments (after destruction) is modeled by numerically solving the meteor physics equations, taking into account the curvilinearity of the trajectory. The uncertainty of such modeling is due to the uncertainty in setting the main governing parameters of the equations: the heat transfer coefficient and effective heat of ablation. We study how the angle of meteoroid entry into the atmosphere influences on the scatter in the results of calculations of its velocity, mass loss, energy deposition, trajectory, and meteorite fall location, caused by different ways of setting the heat transfer coefficient and ablation heat.

Flow and heat transfer in a flat confuser is numerically modeled using a three-parameter differential RANS turbulence model supplemented with a transport equation for turbulent heat flow. The influence of the angle of inclination of the confuser wall and the Reynolds number on the characteristics of flow and heat transfer in the boundary layer is considered. The calculation results are compared with the experimental data.

This paper presents experimental studies of a supersonic flow around axisymmetric annular cavities on pointed cylindrical bodies at angles of attack. A single- and multimode flow around the cavity is observed in a wide range of determining parameters (relative length of the cavity L/h and angle of attack α). Reversible and irreversible switching of flow modes in the cavity occurs with a continuous change in the determining parameters. In a closed cavity, with an increase in the angle of attack, a local pressure increase is recorded on the leeward side of the rear step, exceeding the pressure on the windward side of the same step.

A series of experiments are carried out on the shock tube of the Institute of Mechanics of Lomonosov Moscow State University to measure the evolution of radiation absorption in shock-heated oxygen in the wavelength range of 213–260 nm at a gas pressure of 1 Torr and shock wave velocities from 3.4 to 4.5 km/s. Based on a comparison of the experimental data with the results of calculations using the collision-radiation model, the influence of bound-bound and bound-unbound transitions in the Schumann–Runge system on the absorption properties of oxygen is analyzed.

The mode of a supersonic flow around a cavity depends on the parameters of the incoming flow and the geometry of the cavity. In a certain range of ratios between the length and depth of the cavity, both open and closed flow modes in the cavity are possible. An important practical problem is to find ways to control the flow modes in the cavity, and in particular, ways to expand the region of favorable open flow modes. This paper presents the results of an experimental study of a supersonic flow around an annular cavity formed by a coaxial conical tip and a cylindrical body connected by a cylindrical rod. A perforated interceptor is used to control the flow mode in the cavity at different angles of the tip cone. With a continuous change in the length of the cavity in the flow, the boundaries of the regions of the single-mode and multimode cavity flow are determined. The data obtained show the possibility of significantly expanding the region of the fopen flow mode in the cavity.

An analytical model for calculating the radiation intensity in shock-heated air is constructed, taking into account the absorption of radiation as it passes across the shock wave along the observation beam of the measuring systems of experimental installations. Using the model, an assessment is made of the effect of absorption on the broadening of spectral lines, as well as on the radiation intensity of high-temperature air in the vacuum-ultraviolet and visible spectral regions.