FLEET Velocimetry for Aerodynamics

Long-lasting emission from femtosecond excitation of nitrogen-based flows shows promise as a useful mechanism for a molecular tagging velocimetry instrument. The technique, known as femtosecond laser electronic excitation tagging (FLEET), was invented at Princeton a decade ago and has quickly been adopted and used in a variety of high-speed ground test flow facilities. The short temporal scales offered by femtosecond amplifiers permit nonresonant multiphoton excitation, dissociation, and weak ionization of a gaseous medium near the beam's focus without the generation of a laser spark observed with nanosecond systems. Gated, intensified imaging of the resulting emission enables the tracking of tagged molecules, thereby measuring one to three components of velocity. Effects of local heating and acoustic disturbances can be mitigated with the selection of a shorter-wavelength excitation source. This review surveys the development of FLEET over the decade since its inception, as it has been implemented in several test facilities to make accurate, precise, and seedless velocimetry measurements for studying complex high-speed flows.

OuroborosBEM: a fast multi-GPU microscopic Monte Carlo simulation for gaseous detectors and charged particle dynamics

The design of gaseous detectors for accelerator, particle and nuclear physics requires simulations relying on multi-physics aspects. In fact, these simulations deal with the dynamics of a large number of charged particles interacting in a gaseous medium immersed in the electric field generated by a more or less complex assembly of electrodes and dielectric materials. We report here on a homemade software, called ouroborosbem, able to tackle the different features involved in such simulations. After solving the electrostatic problem for which a solver based on the boundary element method (BEM) has been implemented, particles are tracked and will microscopically interact with the gas medium. Dynamical effects have been included such as the electron-ion recombination process, the charging-up of the dielectric materials and other space charge effects that might alter the detector performances. These were made possible thanks to the nVidia CUDA language specifically optimised to run on Graphical Processor Units (GPUs) to minimize the computing times. Comparisons of the results obtained for parallel plate avalanche counters and GEM detectors to literature data on swarm parameters fully validate the performances of ouroborosbem. Moreover, we were able to precisely reproduce the measured gains of single and double GEM detectors as a function of the applied voltage.

SPECTRAL FEATURES AND HYDROGEN BOND STRUCTURE OF AQUEOUS SOLUTIONS OF ETHANOL

The aim of this work is develop an approach that makes it possible to study the spectral properties and structure of intermolecular hydrogen bonds in aqueous solutions of ethanol formed in systems whose existence in a gaseous medium or an isolated state is practically impossible. This approach bases on the combined use of infrared spectroscopy and molecular dynamics (MD) methods. An analysis give the structural reorganization of water molecules depending on the concentration of ethanol alcohol. It has been shown that the method of molecular dynamics with classical force fields makes it possible to explicitly take into account the molecules of the solvent and solute, and, thus, to investigate hydrogen bonds in the system and to interpret with the experimental data obtained by vibrational spectroscopy.

Theoretical basis for the formation of damaging factors during the coal aerosol explosion

Purpose. Assessing the process of damaging factors formation during the coal aerosol explosion in mine workings on the basis of theoretical research of the explosion of coal dust deposits in order to substantiate promising methods of protecting miners from their impact. Methods. An integrated approach is used, which includes a critical analysis of literature data on the occurrence and development of coal aerosol explosions in mine workings; theoretical research into the state of the gaseous medium at the characteristic points of the development diagram of the coal dust deposits explosion as a result of mining operations based on the laws of classical physics and chemistry. Findings. The main aspects of the explosion mechanism of dust in a powdery state, accumulated on the surfaces along the mine working perimeter, and the formation of such negative factors as the effect of gaseous medium accelerated movement, have been revealed; high temperature formed during coal and methane detonative combustion; increased gas pressure. The revealed aspects of the dust explosion mechanism make it possible to determine the main directions for protection of miners caught in the explosion. The diagram of the development of settled coal dust explosion along the mine working with normal ventilation conditions, taking into account the influence of seismic waves, has been improved. Originality. Analytical dependences, reflecting the value of gas energy at characteristic points of the diagram, have been determined, and the dynamics of the formation of negative factors caused by the explosion have been revealed. Practical implications. Possible ways of protecting miners from the impact of negative factors caused by the coal aerosol explosion and reducing the severe consequences of such accidents are proposed.

PROPERTIES OF TUBES FROM Zr-1% Nb ALLOY AFTER THERMOCHEMICAL TREATMENT AND HYDROGENATION

The influence of treatment in controlled gas environments with subsequent hydrogenation on the physical and mechanical characteristics of the Zr-1% Nb zirconium alloy has been investigated. The surface hardness and the size of the diffusion-hardened layer of the ring-samples cut from fuel tubes from the Zr-1% Nb alloy after treatment in oxygen- and nitrogen-containing gaseous media with subsequent saturation with hydrogen have been established. The influence of the parameters of the gaseous medium and the modes of thermochemical treatment (TCT) of specimens-rings on the destructive stresses under static load at temperatures of 20 and 380 °C is shown. It was revealed that treatment in the investigated gas environment increases the resistance to hydrogen saturation and has a positive effect on the long-term strength of ring specimens from the zirconium alloy Zr-1% Nb.

Collisions of Liquid Droplets in a Gaseous Medium under Conditions of Intense Phase Transformations: Review

The article presents the results of theoretical and experimental studies of coalescence, disruption, and fragmentation of liquid droplets in multiphase and multicomponent gas-vapor-droplet media. Highly promising approaches are considered to studying the interaction of liquid droplets in gaseous media with different compositions and parameters. A comparative analysis of promising technologies is carried out for the primary and secondary atomization of liquid droplets using schemes of their collision with each other. The influence of a range of factors and parameters on the collision processes of drops is analyzed, in particular, viscosity, density, surface, and interfacial tension of a liquid, trajectories of droplets in a gaseous medium, droplet velocities and sizes. The processes involved in the interaction of dissimilar droplets with a variable component composition and temperature are described. Fundamental differences are shown in the number and size of droplets formed due to binary collisions and collisions between droplets and particles at different Weber numbers. The conditions are analyzed for the several-fold increase in the number of droplets in the air flow due to their collisions in the disruption mode. A technique is described for generalizing and presenting the research findings on the interaction of drops in the form of theoretical collision regime maps using various approaches.

Determination of the Parameters of the Target Heterogeneous Medium During Centrifugal Arc Dispersion of Hard Alloys

The article considers the ballistic parameters of the trajectories of high-density alloy particles moving in a gaseous medium, accompanied by a phase transition of the of the particle material. A technique has been developed for determining the parameters of the target depending on the physical and mechanical characteristics of the materials of the captured particles and target layers. The possibility of maintaining the spheroidal shape of particles during the electric arc dispersion of high-density alloys has been determined.