Alexander V. Zaitsev

This study is aimed at developing methods for the experimental and numerical simulation of the outflow of underexpanded gas jets into a rarefied medium. The numerical method is based on using Navier–Stokes equations in the continuum flow regime and the direct simulation Monte Carlo method in the transitional flow regime. The experimental method includes the modeling of jet flows in the LEMPUS-2 gas-dynamic setup with electron beam diagnostics for the jet density measurements. The results of the experimental modeling for the nozzles of various diameters confirm that a key parameter determining the jet structure is the Reynolds number based on the characteristic length Re_L. The results of the numerical simulations agree well with the experimental data both for the maximum values of the Re_L considered (approximately 30) when a barrel jet structure with Mach disks is formed and for the minimum values (approximately 4) when no Mach disks are formed. In the entire range of parameters, significant thermal nonequilibrium is observed at all jet segments where the measurements are performed.

Numerical modeling of jet flows of nitrogen expanding through a nozzle into a vacuum chamber has been carried out. A hybrid method is used in computations: cont

A model of the argon condensation process has been developed for the direct simulation Monte Carlo (DSMC) method. The model includes the following processes: formation of dimers, merging of clusters, sticking of monomers to clusters, evaporation of monomers from clusters, and inelastic collisions between particles. The proposed model is implemented in the DSMC code SMILE++. The model is then verified and validated. Calculations of jet flows exhausting into a rarefied medium are performed on the basis of the proposed model.

A nitrogen jet expanding during its exhaustion from a nozzle into a vacuum chamber is numerically simulated by a hybrid approach. The flow parameters in the nozzle and in the near field of the jet are determined by solving the Navier–Stokes equations by using the ANSYS Fluent software. The gas flow at large distances from the nozzle exit is modeled by the Direct Simulation Monte Carlo method by using the SMILE software system. Such an approach makes it possible to perform sufficiently accurate simulations in the near field of the jet; moreover, the temperature nonequilibrium of the expanding gas jet and other effects of rarefaction in the far field of the jet are taken into account. The approach is verified by using various approximate analytical models of gas exhaustion into vacuum. A comparison of the numerical results with available experimental data shows that they are in good agreement.

Results of experiments and numerical modeling of gas-powder flow for laser cladding are presented. Numerical simulation is based on solving Navier-Stokes equations with Lagrange approach for particle. The main attention is paid to the process of interaction between powder particles and nozzle walls. Simple particle-wall interaction model was suggested and verified with experiments for gas-powder jet formed in the long tubes with different diameters. The model was used for simulation of powder transport in the coaxial nozzle for laser cladding.

A method of analytical and numerical calculation of the absorption coefficient of laser radiation was proposed and tested based on the results of a simplified experimental cutting setup. The results are compared with available theoretical predictions and experimental data the literature forecasts in a wide range of angles of inclination. A significant difference between the absorption coefficients for mild steel used in the theory and reconstructed from experimental data. The obtained absorption coefficient can be used for further modeling of laser material processing technologies.

In this work, one of the main scientific and technological problem of laser cladding technology, increasing the powder usage coefficient are studied. Two-phase gas-powder flow are investigated. Physical and mathematical models of powder transportation process are discussed. The structure of gas-powder flows formed by the laser-cladding nozzle and the accuracy of focusing the jet of powder being researched. The main attention is focused on interaction between powder particles and nozzle wall. Presented data collected by gas-powder jet optic diagnostic, results of numerical simulation and their comparison.

In this work, physical and mathematical models of powder transportation by gas during laser cladding are discussed. The main attention is paid to modeling the interaction of powder particles and nozzle walls. The results of numerical simulation and experimental data are compared.

A method of analytical and numerical calculation of the absorption coefficient was proposed and tested based on the results of a simplified experimental cutting setup. The results are compared with the literature forecasts in a wide range of angles of inclination. It was found a significant difference between the absorption coefficients used in the theory and reconstructed their experimental data. The obtained absorption coefficient can be used for further modeling of laser material processing technologies.

Owing to its high mass and volume heats of combustion, boron is a promising component of solid propellants for air-breathing engines. Its application is limited by difficulties of organizing...