Numerical simulation of underexpanded supersonic jets impingement on an inclined flat plateEpikhin, A. S.; Elizarova, T. G.
2021 Thermophysics and Aeromechanics
doi: 10.1134/s0869864321040028
The paper presents the results of numerical simulation of complex shock-wave structures arising from an under-expanded jets impingement on an inclined flat plate. The plate deflection angles equal to 45°, 60°, and 90° are investigated, which corresponds to different types of shock waves interference. The gas-dynamic characteristics are calculated using the OpenFOAM software package with the QGDFoam solver. This solver based on a system of regularized (quasi-gas dynamic) equations. The numerical simulation results of the flowfields and pressure distributions at the plate are compared against the results of the Kurganov-Tadmor scheme and with experimental data. The features of the applied numerical approach for simulation of complex shock-wave structures with triplet points, contact discontinuities, and low-entropy flows are identified.
Experimental study of stratified flow hydrodynamics for concurrent mixing streamsDmitriev, S. M.; Khrobostov, A. E.; Legchanov, M. A.; Borodin, S. S.; Barinov, A. A.; Konovalov, I. A.; Chesnokov, A. A.; Makarov, M. A.
2021 Thermophysics and Aeromechanics
doi: 10.1134/s0869864321040041
This paper presents the results of experimental study for turbulent flow performed using a conductometry measurement system. Processing of experimental data produces the estimates for average tracer concentration in the cells of the conductometry sensor, the dispersion for parameter representation, as well as autocorrelation functions and the histograms of probability distribution functions for the measured signal. The experimental data was compared with the results of GEMIX benchmark, which has a similar problem statement and tailored for a study of isothermal and nonisothermal mixing processes (the outcome parameters are found using the PIV method). This comparison demonstrates matching for typical wavelengths concerning the ordered flow structures developing at the streams interface. We also observe compliance for turbulent kinetic energy profiles within the central region of experimental model. Meanwhile, the outer zones have a significant discrepancy with the GEMIX-calculated data. This can be explained by a difference in measurement methods and a higher spatial resolution of the PIV method exceeding that for the conductometry method.
On numerical modeling of aerodynamics of urban developments on unstructured computational gridsValger, S. A.
2021 Thermophysics and Aeromechanics
doi: 10.1134/s0869864321040053
The issue of applicability of unstructured computational grids in the problems of numerical modeling of the aerodynamics of buildings is considered. The analysis of the computational performance and discretization errors on unstructured grids with polyhedral and tetrahedral forms of the grid element is performed on the test problem of the flow around square-section prism. The results of numerical modeling obtained on various types of grids are compared with experimental data on velocity profiles and turbulent kinetic energy in characteristic vertical and horizontal sections in the vicinity of the prism, as well as on the characteristic sizes of separation zones on the prism cover and behind it. When using a polyhedral computational grid, the calculation time is shown to be significantly less, compared to calculations on grids based on tetrahedra, while the calculation results qualitatively and quantitatively reproducing the experimental data. Non-stationary modeling on a polyhedral computational grid is carried out in this work using a vortex-resolving turbulence model. Calculations using the vortex-resolving approach allow refining the parameters of the recirculation zone behind the prism. The calculations are performed in the Fluent 2020R1 solver.
Experimental investigation of spacer grid effect on shear stress distribution in models of fuel assembliesPribaturin, N. A.; Lobanov, P. D.; Randin, V. V.; Kashinsky, O. N.; Kurdyumov, A. S.; Vorobyev, M. A.; Volkov, S. M.
2021 Thermophysics and Aeromechanics
doi: 10.1134/s0869864321040065
To assess the spacer grid effect on the liquid flow disturbance, the shear stress on the surface of a vertical rod — a fuel element simulator — was measured in seven-rod models of fuel assemblies differing in spacer grid sizes, diameter of rods (fuel element simulators), and relative distance between them. Data on axial distribution of shear stress are presented. An increase in the averaged and pulsation wall shear stresses directly behind the grid due to liquid flow disturbance and extinction of this effect far from the grid is shown. The results of this research can be applied to verify the design codes used in hydrodynamic predictions of reactors.
Deposition of oxide nanostructures by nanosecond laser ablation of silicon in an oxygen-containing background gasRodionov, A. A.; Starinskiy, S. V.; Shukhov, Yu. G.; Bulgakov, A. V.
2021 Thermophysics and Aeromechanics
doi: 10.1134/s0869864321040089
The nanosecond laser ablation technique was used to synthesize thin silicon oxide films of various stoichiometry in vacuum and in a background gas. The local oxidation degree of specimens was evaluated using three different characterization methods. It was found that, on increasing the distance to the laser-plume axis, there occurred a monotonic increase in the oxygen content of the films due to their oxidation inhomogeneity. A profound decrease in ablated mass, related to an increased reverse flow of substance to the target, was found to occur when the pressure of the ambient mixture was increased from 20 to 60 Pa. A comparison was made of the oxidation efficiencies of the films heated at the stage of their synthesis and at the stage of annealing of already formed films. It is shown that the composition of the films could be controlled by varying the inert-gas pressure at the constant pressure of the chemically active component in ambient mixture.
Instabilities of blow-down type Venturi cavitation considering thermodynamic effectZhang, H. C.; Chen, H.; Xiang, L.; Zuo, Z. G.; Liu, S. H.
2021 Thermophysics and Aeromechanics
doi: 10.1134/s0869864321040107
It is known that thermodynamic effect of cavitation could not be ignored in liquids such as cryogenic liquids, refrigerants, and high temperature water. This effect could delay and suppress the further development of cavitation, thus improve the suction performance in cases of hydraulic machinery. However, the influence of thermodynamic effect on cavitation instabilities has not been adequately discussed. For this purpose, a series of systematically designed experiments of Venturi cavitation in a blow-down type cavitation tunnel have been carried out, using water as the working liquid at different temperatures. For the first time, the cavitation instabilities were analyzed and identified with controlled degrees of thermodynamic effect Σ*. The mean cavitation length Lcav∗\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$L_{{\rm{cav}}}^ \ast$$\end{document} and three types of cavitation instabilities were recognized through an image post-processing method. A decrease of Lcav∗\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$L_{{\rm{cav}}}^ \ast$$\end{document} is observed with an increasing Σ*. For all Σ* conditions, cavitation surge (system instability), cloud shedding, and oscillations of the attached cavitation length occur at small, middle, and large pressure recovery number (κ) conditions, respectively. The thermodynamic effect mainly influences the range of κ for different cavitation instabilities. Cavitation surge and transition from cloud shedding to oscillations of attached cavitation length shift to a lower κ with an increasing Σ*.