The mixing due to helical flows in curved micro channels is investigated. A new chaotic

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The wake behind a quarter-of-ring concave curved cylinder is investigated in this paper by means of direct numerical simulations. The plane of curvature is aligned with the uniform incoming flow. We have appended straight extensions to both ends of the curved part of the cylinder, such that free ends are eliminated from the simulations. The effect of the vertical extension, i.e., the straight extension with its axis normal to the inflow, is carefully studied and turns out to be significant. The results from several different Reynolds numbers (Re = 100-500) are presented, from which a clear picture of the wake transition behind this configuration could be sketched. The concave curved cylinder wake consists of different flow regimes along the span. Oblique shedding, vortex dislocations, and various shedding frequencies are captured in different flow regimes. At Re 300, the flow regimes change abruptly, but at Re = 400 and 500, the changes are continuous, so the boundaries between them are difficult to observe. A frequency band, instead of one single dominating frequency, manifests itself in the three-dimensional (3D) energy spectrum.

Recovery of cobalt and lithium from spent Li-ion batteries (LIBs) has been studied using ultrasound-assisted leaching. The primary purpose of this work is to investigate the effects of ultrasound on leaching efficiency of cobalt and lithium. The results were compared to conventional leaching. In this study sulfuric acid was used as leaching agent in the presence of hydrogen peroxide. The cathode active materials from spent battery were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) before and after leaching. Effects of leaching time, leaching temperature, HSO concentration, HO concentration, solid/liquid ratio, and ultrasonic power have been studied. Optimal leaching efficiency of 94.63% for cobalt, and 98.62% for lithium, respectively, was achieved by using 2 M HSO with 5% (v/v) HO at a solid/liquid ratio of 100 g/L, and an ultrasonic power of 360 W, and the leaching time being 30 min under 30 °C. Compared with conventional leaching, the ultrasound-assisted leaching gave a higher leaching rate and improved leaching efficiency under the same experimental conditionals. The kinetic analysis of ultrasound-assisted leaching showed that the activation energy of cobalt and lithium were 3.848 KJ/mol and 11.6348 KJ/mol, respectively, indicating that ultrasound-assisted leaching of cobalt and lithium from spent LIBs was controlled by diffusion.

An individual-based model (IBM) to simulate the movement of a single fish through a vertical slot fishway has been developed. The turbulent water flow in the fishway was first obtained using CFD-software. Trajectories of live fish measured by Rodrigues et al. (2011) were superimposed on several different parameters characterising the flow, such as the turbulent kinetic energy (TKE). The correlations between these hydrodynamic parameters and the measured trajectories were examined and TKE was identified as the single most important stimulus. To mimic positive rheotaxis, the mean velocity was adopted as a secondary agent. The new Lagrangian IBM-model was combined with the Eulerian CFD-model to an Eulerian-Lagrangian Agent Method. This ELAM approach was used to compute the trajectory of a virtual fish. The simulated trajectories were in good agreement with their measured counterparts in the same fishway. Both the preferred direct route and the alternative longer route through an active pool were faithfully reproduced.

Flow around a step cylinder at the Reynolds number 150 was simulated by directly solving the full Navier-Stokes equations. The configuration was adopted from the work of Morton and Yarusevych [“Vortex shedding in the wake of a step cylinder,” Phys. Fluids 22, 083602 (2010)], in which the wake dynamics were systematically described. A more detailed investigation of the vortex dislocation process has now been performed. Two kinds of new loop vortex structures were identified. Additionally, antisymmetric vortex interactions in two adjacent vortex dislocation processes were observed and explained. The results in this letter serve as a supplement for a more thorough understanding of the vortex dynamics in the step cylinder wake.

The three-dimensional flow field around a prolate spheroid has been obtained by integration of the full Navier-Stokes equations at Reynolds numbers 0.1, 1.0 and 10. The 6:1 spheroid was embedded in a Cartesian mesh by means of an immersed boundary method. In the low-Re range, due to the dominance of viscous stresses, an exceptionally wide computational domain was required, together with a substantial grid refinement in vicinity of the surface of the immersed spheroid. Flow fields in equatorial and meridional planes were visualized by means of streamlines to illustrate Reynolds number and attack angle effects. Drag and lift forces and torques were computed and compared with the most recent correlation formulas. The largest discrepancies were observed for the moment coefficient whereas the drag coefficient compared reasonably well.

The wake behind a 6:1 prolate spheroid at 45° incidence has been studied by means of direct numerical simulations (DNSs). The Reynolds number based on the minor axis of the spheroid was 3000 as compared to 1000 in our preceding study [Jiang et al., “The laminar wake behind a 6:1 prolate spheroid at 45° incidence angle,” Phys. Fluids 26, 113602 (2014)]. The resulting wake is no longer laminar and the transitional wake is fundamentally unsteady and highly asymmetric from the very beginning. A substantial side force resulted from the asymmetric pressure field. No signs of vortex shedding could be observed. The forces and the flow field around the spheroid exhibited a dominant periodicity with a surprisingly low Strouhal number of 0.0733. One part of the counter-rotating vortex pair which dominated the near-wake broke down into small-scale vortices as soon as the vortex left the shadow behind the spheroid. The other part appeared as a helical vortex inside which the mechanical energy was conserved over a substantial length. The axial flow within this vortex tube experienced a sudden change from having maximum to minimum at the vortex center while maintaining the sign of the circulation. The severe asymmetry of the wake is ascribed to a global instability and may impact on submarine maneuverability.