Extension of staggered-grid-based AUSM-family schemes for use in nuclear safety analysis codes

To overcome the numerical difficulties of the density-based method for low-Mach-number two-phase flow, this paper adopts the AUSM${}^{+}$ and AUSMDV schemes based on a staggered-grid arrangement. The water faucet, air-water shock tube, oscillating manometer and air-water phase separation problems are used as benchmark tests to validate the implementation of the generic four-equation two-fluid model. The present results reveal the advantages of using staggered-grid-based AUSM${}^{+}$ and AUSMDV schemes over the collocated-grid-based counterpart. With a staggered-grid arrangement, odd-even decoupling issues can be avoided. Thus, no sound speed scaling or additional diffusion terms are needed when using AUSM${}^{+}$ and AUSMDV schemes for low-Mach-number two-phase flow. Furthermore, since the pressure and void fraction are already stored at the interface of the velocity control volume, no interpolation of interfacial pressure is needed for momentum equations. Finally, this study will help integrate AUSM${}^{+}$ and AUSMDV schemes into staggered-grid-based thermal hydraulic codes, e.g. CATHENA, used in the nuclear industry. Moreover, to tackle the stiffness issues in relation to phase appearance and disappearance, we propose a new staggered-grid-based scheme referred to as AUSMFVS, which combines the accuracy of AUSM${}^{+}$ and the stability of FVS.     

Two-phase flow patterns and size distribution of droplets in a microfluidic T-junction: Experimental observations in the squeezing regime

Generating micrometer sized droplets has been studied in a microfluidic system with T-junction geometry 250 μm in internal diameter and with PTFE capillary tubing. Several experiments were conducted by varying the flow rate of the dispersed phase from $2.78\cdot {10}^{-11}{\text{ m}}^3/\text{s}$ to $5.28\cdot {10}^{-9}{\text{ m}}^3/\text{s}$ and that of the continuous phase from $2.78\cdot {10}^{-10}{\text{ m}}^3/\text{s}$ to $1.94\cdot {10}^{-9}{\text{ m}}^3/\text{s}$. The visualization of different flow regimes (drop, plug, and annular) was carried out for three configurations (not inverted in a horizontal position, inverted in a horizontal position, and inverted in a vertical position) for low capillary numbers. The model of Gauss was also chosen for a droplet size distribution in the dispersed phase, with the flow quality x varying from 0.016 to 0.44. The evolution of the drop size distribution as a function of the flow quality in the dispersed phase shows that the variation coefficient of the droplet's diameter is inversely proportional to the flow quality.     

Thermo-viscoplasticity of carbon black-reinforced thermoplastic elastomers

Observations are reported on carbon black–filled thermoplastic elastomer (TPE) in uniaxial loading–unloading tensile tests with various strain rates (ranging from $7\times {10}^{-4}$ to $1\times {10}^{-1}{\text{s}}^{-1}$) at temperatures in the interval from 25 to 90 °C. A constitutive model is derived for the viscoplastic response of a TPE composite at three-dimensional deformations with finite strains. The stress–strain relations involve six adjustable parameters that are found by fitting the experimental data. It is shown that the model correctly describes the observations, and its parameters are affected by temperature and strain rate in a physically plausible way.