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The improved delayed detached Eddy simulation (IDDES) approach used in the part I of this investigation to study the self-ignition and combustion of hydrogen jets in a high-speed transverse flow of hot vitiated air in a duct is extended in the following directions: (i) the wall boundary conditions are modified to take into account the optical windows employed in the experiments; (ii) the detailed chemical kinetic model with 19 reactions is used; (iii) a nonlinear turbulence model is implemented in the code to capture the secondary flows in the duct corners; (iv) the wall roughness model is adapted; (v) the synthetic turbulence generator is imposed upstream of the fuel injection. As a result of improving the mathematical and physical problem statements, a good agreement between the simulation and the experimental database obtained at the LAERTE workbench (ONERA) is achieved. [ABSTRACT FROM AUTHOR]

We successfully synthesized bulk Ba0.6Na0.4Fe2As2 and Sr0.5Na0.5Fe2As2 compounds by high-energy mechanical alloying (MA) technique. The MA process results in homogeneous amorphous phases of BaFe2As2 and SrFe2As2. It was found that the optimum time for high-energy milling in all cases is about 1.5–2 h, and the maximum amount of amorphous phase could be obtained when energy of 50–100 MJ/kg was absorbed by the powder. After a short-term heat treatment, we obtained nearly optimum sodium-doped Ba1−xNaxFe2As2 and Sr1−xNaxFe2As2 superconducting bulk samples. Therefore, MA is a potential scalable method to produce bulk superconducting material for industrial needs. [ABSTRACT FROM AUTHOR]

We performed systematic AC susceptibility and magnetic moment measurements to investigate the vortex dynamics and pinning in single crystals as a function of temperature, frequency, and DC magnetic field. The vortex solid-liquid line was determined, and it can be fitted well with using β = 1.74 ± 0.1–1.91 ± 0.1, where Tp is the peak position on an imaginary part of the AC susceptibility plot (), for H ab. It indicates a rather high pinning strength of the vortex system. The activation energy U0 was determined from thermally activated flux creep theory and reached 6700 ± 1100 K at low fields, suggesting strong vortex pinning. A field dependence of U0(H ab) ∼ Ha with a = 0.47(4) suggests thermally activated plastic pinning or caused by planar defects. Magnetic moment measurements also confirmed strong pinning in the superconductor, and the superconducting response gives the main contribution to the M(H) hysteresis. Additionally, we show long-range ordering of the Eu2 + sublattice according to the AC susceptibility measurement data. [ABSTRACT FROM AUTHOR]

We present the study of the superconducting order parameter in single crystals of alkali metal EuCsFe 4 As 4 pnictide belonging to the novel 1144 family, turning to the superconducting state in the stoichiometric composition at critical temperature T c ≈ 37 K, and showing an antiferromagnetic ordering below T c . In the superconducting state, using incoherent multiple Andreev reflection effect spectroscopy of superconductor-thin normal metal-superconductor (SnS) junctions, we show a multiple-gap superconductivity with possibly anisotropic large SC gap with an extended s-wave symmetry, and isotropic small SC gap. We directly determined the magnitudes, characteristic ratios, and temperature evolution of the superconducting gaps. The latter are found to be typical for a superconductor with rather weak interband interaction between SC condensates in the k-space. [ABSTRACT FROM AUTHOR]

We report crystal growth and characterization of 4 new ternary layered bismuthides with compositions KZn2Bi2 (I), RbZn2Bi2 (II), RbCd2Bi2 (III), and CsCd2Bi2 (IV) that belong to the vast 122 family of compounds. Single crystals were grown by self‐flux technique and characterized by a combination of powder X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, and single crystal X‐ray diffraction. All new compounds crystallize in the layered ThCr2Si2 structure type and exhibit the plate‐like morphology with weak bonding between layers. A significant structural difference between ACd2Bi2 and AZn2Bi2 is found and discussed. [ABSTRACT FROM AUTHOR]

Swirling flames are widely used in engineering to intensify mixing and stabilize combustion in gas turbine power plants and industrial burners. Swirling induces new instability modes, leading to intensification of coherent structures, asymmetric geometry, vortex core precession, and flame oscillations. Large-Eddy Simulation (LES) has the capability to furnish more accurate and reliable results than the simulations based on Reynolds-averaged Navier–Stokes equations (RANS). Subgrid-scale models in LES need to describe the backscatter (local transfer of kinetic energy from small scales to larger scales) that is intensified in swirling flames. In this paper, the Differential Subgrid Stress Model (DSM), previously developed by the authors, is assessed using an experimental database from Sydney University on swirl-stabilized turbulent unconfined non-premixed methane-air flame. Regime without vortex precession is simulated numerically using the DSM and Smagorinsky subgrid-scale model. Experimental measurements of mean velocity, profiles of mass fractions, and temperature are used for comparison with the simulation data. The standard Smagorinsky model is considered the basic approach. Differences in the flow field statistics obtained in both subgrid-scale LES models are analyzed and discussed. The importance of taking the backscatter into account is highlighted. [ABSTRACT FROM AUTHOR]

The paper deals with the self-ignition and combustion of hydrogen jets in a high-speed transverse flow of hot vitiated air in a duct. The Improved Delayed Detached Eddy Simulation (IDDES) approach based on the Shear Stress Transport (SST) model is used, which in this paper is applied to a turbulent reacting flow with finite rate chemical reactions. An original Adaptive Implicit Scheme for unsteady simulations of turbulent flows with combustion, which was successfully used in IDDES simulation, is described. The simulation results are compared with the experimental database obtained at the LAERTE experimental workbench of the ONERA—The French Aerospace Laboratory. Comparison of IDDES with experimental results shows a strong sensitivity of the simulation results to the surface roughness and temperature of the duct walls. The results of IDDES modeling are in good agreement with experimental pressure distributions along the wall and with the results of videoregistration of the excited radical chemiluminescence. [ABSTRACT FROM AUTHOR]

In the stoichiometric iron-based superconductor EuRbFe4As4, superconductivity coexists with a long-range magnetic ordering in Eu layers. Using high-resolution transmission electron microscopy (HRTEM), we observed an atomic structure of as-grown EuRbFe4As4 crystals. HRTEM shows that crystals have two-dimensional intrinsic nanoinclusions established to be the RbFe2As2 (122) phase with a volume fraction of ~5.6%. In contrast with the CaKFe4As4 compound, similar inclusions are not superconducting down to 2 K, and no second magnetization peak was observed in the magnetization measurements at low temperature with B ‖ ab. We show that the non-superconducting 122 phase nanoinclusions could act as 2D pinning centers. [ABSTRACT FROM AUTHOR]

Abstract Fast technologies for numerical simulation of high-speed flows in ducts, developed in TsAGI, are described. The examples are presented of the application of experimental data, obtained at T-131 wind tunnel, for validation of the developed numerical technologies: 1) validation of 2.5D and 3D calculations of flow in the elliptic combustor with hydrogen supersonic combustion that was studied within HEXAFLY-INT international project; 2) validation of 2D and 2.5D calculations of flow in high-speed model combustor duct with step-like expansion. Preparation of new series of experiments, oriented on validation of turbulent combustion models, is described. [ABSTRACT FROM AUTHOR]