Generalized equilibria for color-gradient lattice Boltzmann model based on higher-order Hermite polynomials: A simplified implementation with central moments.

We propose generalized equilibria of a three-dimensional color-gradient lattice Boltzmann model for two-component two-phase flows using higher-order Hermite polynomials. Although the resulting equilibrium distribution function, which includes a sixth-order term on the velocity, is computationally cumbersome, its equilibrium central moments (CMs) are velocity-independent and have a simplified form. Numerical experiments show that our approach, as in Wen et al. [Phys. Rev. E 100, 023301 (2019)2470-004510.1103/PhysRevE.100.023301] who consider terms up to third order, improves the Galilean invariance compared to that of the conventional approach. Dynamic problems can be solved with high accuracy at a density ratio of 10; however, the accuracy is still limited to a density ratio of 1000. For lower density ratios, the generalized equilibria benefit from the CM-based multiple-relaxation-time model, especially at very high Reynolds numbers, significantly improving the numerical stability.

Facile Two-Step Synthesis of 1,10-Phenanthroline-Derived Polyaza[7]helicenes with High Fluorescence and CPL Efficiency.

A facile two-step synthesis of aza[7]helicenes possessing a 6-5-6-6-6-5-6 skeleton from commercially available 2,9-dichloro-1,10-phenanthroline via double amination with aniline derivatives followed by hypervalent iodine reagent-mediated intramolecular double-NH/CH couplings was developed. Single-crystal X-ray analyses of the helicenes revealed unique structures, including both a significantly twisted center and planar terminals of the skeleton. The azahelicenes show high fluorescent quantum yields (Φs) under both neutral (Φ: 0.25-0.55) and acidic conditions (Φ: up to 0.80). An enantiomerically pure aza[7]helicene showed high circularly polarized luminescence (CPL) activity under both neutral and acidic conditions (glum : up to 0.009).

Lifetime-based measurement of stress during cyclic elastic deformation using mechanoluminescence of SrAl2O4:Eu²âº.

The present study focused on the rise time and decay times of mechanoluminescence (ML) during cyclic elastic deformation of SrAl2O4:Eu²âº. The time constants during compression and decompression, τup and τdown, respectively, did not change from the 2nd to the 5th cycle. Both τup and τdown were expressed by a linear function of the maximum load and the inverse of the loading rate. τup depended only on the loading time, whereas τdown was affected by the loading time and the rate of change of the strain energy. Measuring τdown may enable evaluation of the loading conditions even under cyclic loading and may enhance the practicality of a ML phosphor.

Lifetime-based measurement of stress using mechanoluminescence of SrAl2O4:Eu2+.

The stress and loading rate on disks of SrAl2O4:Eu mixed epoxy resin were measured by a lifetime-based method. The concentration of the mechanoluminescence (ML) phosphor and the excitation power did not affect the measured lifetime. The lifetime was proportional to the stress and was inversely proportional to the loading rate. The concentration, the excitation power, the stress, and the loading rate affected the peak intensity of ML, while previous work estimated the stress using the absolute intensity under well-controlled excitation and concentration conditions. The method used here can shorten the measurement time and enhance the practicality of a ML phosphor.

Combined velocity and temperature imaging of gas flow in an engine cylinder.

A combined velocity and temperature measurement method using a high-speed camera, a pulsed UV laser, and temperature-sensitive phosphor particles is proposed. The temperature was calculated from the phosphorescence lifetime, while the velocity was obtained from images of the phosphor particles during a single decay. This method was applied to in-cylinder measurements of gas flow at high temperatures under motoring conditions. Tumble flow was observed at the top dead center. The temperature-change dependence on the crank angle agrees qualitatively with the gas temperature and the pressure.

Measurement of the density of CO(2) solution by Mach-Zehnder interferometry.

The density of CO(2) solution was measured by using Mach-Zehnder interferometry in the pressure range from 5.0 to 12.5 MPa, at temperatures from 273.25 to 284.15 K, and CO(2) mass fraction in solution up to 0.061. It was found that the density difference between the CO(2) solution and pure water at the same pressure and temperature is monotonically linear with the CO(2) mass fraction. The slope of this linear function, calculated by experimental data fitting, is 0.275.

Numerical visualization of two-phase plume formation in a stratification flow environment.

Evolution of two-phase plumes driven by air bubble buoyancy in a stratification ambient in a rectangular tank is visualized numerically by means of two-phase flow theory and large-eddy simulation technology. With a focus on the discrete nature of the buoyant dispersed phase and the role of momentum exchange between two phases in plume formation, we investigated the phenomena of mass entraining-in and peeling-out for continuous phase plume, which may result from a complicated and intricate interplay with phase interaction and dynamic stability of the stratification ambient, respectively. Numerical simulations show that although mass entraining-in and peeling-out appear to be distinguished entirely in the vertical direction, they interact or couple locally within inner of the plume and present a discontinuity in nature. The numerically visualized three-dimensional density field also indicates the same plume characteristics.

Flow characteristics of two immiscible liquid layers subjected to a horizontal temperature gradient.

Marangoni convection, driven by an interfacial instability due to a surface tension gradient, presents a significant problem in crystal growth in normal microgravity environments. It is important to suppress and control the convection phenomenon for better material processing, especially in crystal growth by the liquid encapsulated Czochralski or liquid encapsulated floating zone techniques, in which the melt is encapsulated in an immiscible medium. Marangoni convection can occur on the liquid-liquid interface and on the gas-liquid free surface. Buoyancy driven convection can also affect and complicate the flow. In the study we report here, experiments were carried out with two liquid layers, silicone oil and fluorinert, in an open and enclosed rectangular cavity. The flow in the cavity was subjected to a horizontal temperature gradient. The interactive flow near the liquid-liquid interface was measured by the particle image velocimetry technique. The measured flow field is in agreement with numerical predictions. Free surface fluctuations with several dominant frequencies were also measured.