Simulation and Experiment Research on Liquid Channel of Diffuser Blade by Electrochemical Machining

Aiming to solve the problems of the low electrolyte flow rate at leading edge and trailing edge and poor uniformity of the end clearance flow field during the electrochemical machining (ECM) of diffuser blades, a gap flow field simulation model was established by designing three liquid-increasing channels at the leading edge and the trailing edge of the cathode. The simulation results indicate that the liquid-increasing hole channel (LIHC) with an outlet area S of 1.5 mm2 and a distance L from channel center to edge point of 3.2 mm achieves optimal performance. In addition, the experiment results show that the optimized cathode with liquid-increasing hole channel (LIHC) significantly improves the machining efficiency, accuracy and surface quality. Specifically, the feed speed increased from 0.25 mm/min to 0.43 mm/min, the taper decreased from 4.02° to 2.45°, the surface roughness value of blade back reduced from 1.146 µm to 0.802 µm. Moreoever, the roughness of blade basin decreased from 0.961 µm to 0.708 µm, and the roughness of hub reduced from 0.179 µm to 0.119 µm. The results prove the effectiveness of the proposed method, and can be used for ECM of other complex structures with poor flow field uniformity.

Flow and wake characteristics associated with large wood to inform river restoration

Wood is an integral part of a river ecosystem and the number of restoration projects using log placements is increasing. Physical model tests were used to explore how the wood position and submergence level (discharge) affect wake structure, and hence the resulting habitat. We observed a von-Kármán vortex street (VS) for emergent logs placed at the channel center, while no VS formed for submerged logs, because the flow entering the wake from above the log (sweeping flow) inhibited VS formation. As a result, emergent logs placed at the channel center resulted in ten times higher turbulent kinetic energy compared to submerged logs. In addition, both spatial variation in time-mean velocity and turbulence level increased with increasing log length and decreasing submergence level. Submerged logs and logs placed at the channel side created a greater velocity deficit and a longer recirculation zone, both of which can increase the residence time in the wake and deposition of organic matter and nutrients. The results demonstrate that variation in log size and degree of submergence can be used as a tool to vary habitat suitability for different fish preferences. To maximize habitat diversity in rivers, we suggest a diverse large wood placement.

Effects of three floating treatment wetland arrangements on the flow field of a channel

<p>Floating treatment wetlands (FTWs) constitute a nature-based solution that promotes water, stormwater and wastewater treatment by using vegetation growing hydroponically on top of a floating mat. One of the advantages of FTWs is not requiring land space to install them, since FTWs are put directly on the water body's surface. Consequently, FTWs can have the potential to affect the flow field, inducing preferential paths and short-circuit, for instance, which may be controlled by how the FTWs are arranged on the water surface. This study aims to numerically simulate the flow field for three FTW arrangements displayed in a channel reach, in order to assess the hydrodynamic differences between each arrangement. In Arrangement 1, three FTWs in series will be installed at the channel center. Arrangement 2 will be formed by three FTWs in series, each one spanning the channel width. Finally, Arrangement 3 will be formed by two FTWs displayed at each margin of the channel. The total FTW volume will remain constant for all arrangements. The simulations will be performed in Computational Fluid Dynamics (CFD), using a validated FTW model from laboratory experiments.</p>

Magneto-hydrodynamic (MHD) micropump of nanofluids in a rotating microchannel under electrical double-layer effect

We investigate the electroosmosis of nanofluid in a rotating microfluidic channel under the influence of an applied magnetic field. We bring out the rotation-induced complex flow dynamics in the channel as modulated by the nanoparticle driven modifications in the viscous drag. In particular, we observe the flow reversal at the center of the channel, emerging from an intricate competition among different forcings under consideration. We identify the critical rotation Reynolds number, signifying the critical strength of channel rotation relative to the viscous resistance to the flow, for which the flow reversal at the channel center sets in. We demonstrate that the strength of the flow reversal for higher rotation Reynolds number decreases, since higher rotation Reynolds number breaks the interparticle interactions, leading to an enhancement in the effective viscosity of the fluid. Finally, we explain the consequential effects of colloidal suspensions of nanoparticle as realized through the particle concentration and agglomeration size on the alterations in the volume transport rates in the channel.

Drag on Sticky and Janus (Slip-Stick) Spheres Confined in a Channel

Flow over a sphere is a frequently occurring phenomenon in a range of industries. The sphere is confined in a channel in most of these applications. Therefore, it is important to understand the effect of confinement on the hydrodynamics of the flow around a sphere placed in a channel. These spheres can be bubbles, solid particles or droplets resulting in different boundary conditions (stick or slip) on the surface of the sphere. In recent years, Janus spheres having slip and stick boundary conditions on parts of the sphere have gained importance because of their potential applications. In this article, drag coefficient for a spherical particle fixed at the centerline of a channel of square cross-section is obtained computationally for stick, slip, and stick-slip surfaces of the sphere for a range of particle Reynolds numbers (1–80) and particle to channel size ratios (0.05–0.80). Further, the position of stick particle in the channel is varied to understand the effect of particle location on the drag coefficient. Correlations are proposed to calculate the drag coefficient for no-slip and Janus particles when the particle is at the channel center.

Dynamic behaviour of multilamellar vesicles under Poiseuille flow

Surfactant multilamellar vesicles flowing in capillaries deform and give rise to a concentrated phase along the channel center in analogy with unilamellar vesicles, droplets and RBCs.

Self-assembly of colloidal micelles in microfluidic channels

The self-assembly of amphiphilic Janus colloids in microfluidic channels under Poiseuille flow is studied using computer simulations. The aggregates grow in the weakly sheared channel center, whereas a distinct cluster breakup occurs in strongly sheared channel regions.