Changes In Velocity Field Research Articles

Effect of characteristic scale on the extrudate swelling behavior of polypropylene melt in a micro‐extrusion process

AbstractThe swelling behavior in micro‐extrusion has a significant effect on the dimensional and shape accuracy of microproducts. In this study, the effect of characteristic scale, defined as the gap of die land in an annular micro‐extrusion die, on the extrudate swelling behavior of viscoelastic melt is analyzed through numerical simulations and micro‐extrusion experiments. The results show that the swelling behavior displays an obvious dependence on the characteristic scale. An increase in the characteristic scale reduces the swell ratio and retards the process to reach the equilibrium state. In contrast, a decrease in the characteristic scale results in a larger magnitude of change in velocity field and faster relaxation development of stress field. The location of the maximum velocity layer for the laminar flow gradually deviates from the geometric center of channel toward the wall of mandrel with the increase in the characteristic scale. Moreover, an increase in the flow rate results in a larger swell ratio for a constant characteristic scale. The elastic effect plays a more dominant role than the viscous effect in determining the viscoelastic swell behavior. It is imperative to consider the complicated swelling behavior and remarkable viscoelastic effect simultaneously in micro‐extrusion process.

Improved energy performance of a PEM fuel cell by introducing discontinuous S-shaped and crescent ribs into flowing channels

Better mass transfer, more uniform temperature distribution, small pressure drop, and improved electrochemical performance can be achieved by designing better flow field in PEM fuel cells. In this paper, based on the concept of a sinusoidal rib, two kinds of discontinuous ribs: S-shaped rib and crescent rib, are proposed and introduced into the flow channels of a PEM fuel cell. Results show that the proposed ribs improve the flow field, and the local convection effect becomes stronger due to the velocity field changes. Moreover, a better distribution of O2 concentration is obtained from the better flow pattern, resulting in an improvement of the electrochemical rate and an increase of the temperature. The pressure drop is effectively reduced, and the electrochemical efficiency is improved by up to 23.61% in the condition of high current density, compared to those of the baseline sinusoidal ribbed flow field.

Assessing Eulerian Indicators for Predicting Mixing in a Blinking Vortex System with Varying Degrees of Continuous Transition

A discontinuous change in sequential velocity fields is known to generate laminar flow mixing through the mechanism of streamline crossing. However, previous research has suggested that a small degree of continuous transition between velocity fields may not necessarily be detrimental. This study therefore used a modified blinking vortex system with varying degree of continuous transition to assess the precise effect that this continuous transition has on mixing performance. This system was studied for the parameters: blinking period, vortex spacing, and the fraction of time spent in transition. Continuous Eulerian indicators were computed to investigate their correspondence with Lagrangian-based metrics, such as Intensity of Segregation, under such conditions. The results showed that up to 30% transition time yielded improvements in mixing, most notably when vortex spacing was large, and this was consistent across different time periods. The mixing prediction by the Eulerian indicators, particularly mobility, showed good agreement with actual mixing quality, albeit not perfectly, suggesting room for refinement in these metrics. Overall, the findings imply that mixing systems, such as continuous pipe flow-based devices, which are designed assuming a discontinuous change in velocity fields, might benefit from the presence of a small degree of continuous transition between discrete states.

VELOCITY CHARACTERISTICS IN WAKE OF A NON-SPHERE BODY AND IN PORE OF POROUS MEDIA COMPOSED OF NON-SPHERES

Details of a velocity field around a prolate spheroid in a steady flow with different angles of attack were investigated by carrying out a hydraulic experiment using the PTV technique. It was found that characteristics of the vortex in the wake of the prolate spheroid were different depending on the angle of attack. It was clearly found that the velocity field changes significantly in the wake. That is to say that there were some areas with strong and weak turbulence and that also some areas with a certain periodic and unclear periodic velocity change with significant change. It was clear that these characteristics depend on the angle of attack of the spheroid. Further, it was confirmed that the distribution of the turbulence intensity was different between the horizontal and vertical components.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/34Dw1CSLEz4

Typhoon wave modelling application for planning the harbor in Danang city, Viet Nam

Analysis of wave propagation in shallow water is considered as one of the important keys in assessing the shoreline evolution, as well as an important basis for assessing the impact of waves on coastal structures. With the purpose of simulating the wave propagation process in the area of Danang Bay, as a basis for assessing the impact of waves and wind on the shoreline evolution as well as giving appropriate construction measures, the study has analysed wave propagation in an area of about 60.3 × 103 km2. Using the MIKE 21/3 module of the Danish Hydraulics Institute, and simulating under the most extreme wave conditions, under the impact of hurricanes level 10, level 13 and level 16 (conditions and storm trajectories based on Nari storm in 2013) as well as the influence of the flow of the Cu De and Han rivers, the study initially showed changes in velocity fields over time, changes in water level and waves in Danang Bay. These results are expected to become the basis for consultation with local authorities in coastal management and disaster prevention, especially in the context of increasingly complex climate change and sea level rise.

Finger-like plumes of suspended sediment in the Colorado River Delta, Gulf of California

The present investigation focused on solving the significance of tidal currents in the sediment resuspension process revealed by satellite imagery in the tidal basin of the Colorado River Delta, located in the northernmost part of the Gulf of California. A depth-integrated finite difference hydrodynamic model, coupled with a suspended sediment transport module, has been applied to calculate the velocity field and potential suspended sediment changes in the delta region. Prescribed values of tidal harmonics were used to force the model at the open boundary of the model domain. The experiments revealed that sediment plumes are generated by the interaction of the tidal flow and the seabed, exposing a remarkable agreement between the crest of sandbanks existing in the delta and the potential sediment resuspension. Close to spring tides, the instantaneous potential transport of sediment in suspension reaches values up to 0.05 m3, integrated over each cell of 280 m × 280 m. The calculations showed that in the shallow coastal area at the gulf's head, sandbank presence is critical for the energy dissipation processes. The crests of sandbanks dissipate much of the energy. The simulated processes are strong evidence that the frictional effect of tidal flow during the initial stages of the spring tides contributes significantly to the sediment's picking up from the seabed going into suspension. These processes shape the plumes of suspended sediment, which extended in the same direction as the sandbanks. Comparison between satellite imagery and modeled distribution of sediment revealed a good agreement between observed and modeled finger-like plumes of sediment. The undulating topography's effect is reflected in the horizontal distributions of energy dissipation, current speed, and kinetic energy.

Numerical simulation of air distribution and CO2 concentration in different air supply locations in winter classroom

In winter, temperature difference between indoor and outdoor is large, and the concentration of indoor CO2 exceeds standard in the closed classroom. In order to achieve better ventilation effect, different outdoor air supply modes are explored to make up for the shortcoming of existing equipment. In this paper, by using FLUENT software, numerical simulation method is used to simulate the temperature field, velocity field changes and differences of classrooms under different air outlets. Also the concentration of CO2 distribution under this condition is simulated, and the best outlet position is obtained through simulation. With the in-depth study of airflow organization, the fresh air system will provide a more comfortable living condition for human beings and serve production and life.

Optimal design of nozzle for filter bag cleaning device of combined air-conditioning based on fluid mechanics

Nozzles are terminal accessories and important parts of equipment for spraying high speed water flow. The shape of nozzle is the main reason that affects the change of pressure and velocity field. For this reason, this paper uses ANSYS software to monitor the pressure and velocity distribution of the internal flow field of nozzle and the high-speed flow field outside the nozzle. In the paper are compared and analyzed the flow field changes due to different nozzle shapes and the influences of various parameters on the nozzle flow field, providing a reference for the rational use of the structural parameters of nozzle.

Analysis of flow field in Si3N4 dry granulation chamber with non-standard composite structure

In order to improve the whirling phenomenon of Si3N4 particles in the granulation chamber, the influence of the structure of the granulation chamber on the internal distribution is explored. Euler Euler’s two-phase flow model is established. The flow field in the combined structure granulation chamber with different layout is simulated. The volume distribution and velocity field change of Si3N4 particles in the combined structure granulation chamber with different layout are analyzed. The results show that the angle between two adjacent composite structures is 20∘, 60∘, 80∘ and completely standard the Si3N4 particles with volume fraction index greater than 0.8 account for 10.2%, 11.5%, 12.5% and 6.7% of the total volume respectively. When the combined structure is completely standard, several small convolutions are found. The whirling phenomenon in the granulation chamber is improved. When the angle between two adjacent composite structures is 20∘, 60∘, 80∘ and complete standard, the proportion of qualified particles is 59%, 64%, 66% and 68%. The fluidity index is 84, 85, 87 and 88, respectively. To sum up, the combination structure of the granulation chamber is a complete standard, it is beneficial to improve the spin phenomenon of Si3N4 particles in the granulation chamber.

Simulation of velocity field changes in a backwater area of the Kama reservoir in different water regime phases

The area of variable backwater of any reservoir is a complex natural and anthropogenic system that changes significantly during a year. The changes are primarily determined by water balance dynamics during a year that is a correlation between input and output water masses into a reservoir or at any part of the water object. Secondly, the input and output of sediment load changes constantly during a year. Transition of sediments from one site to another significantly changes the morphometrical features and morphology of the latter. Finally, the cyclical nature of the changes mentioned above is caused by daily, weekly, and annual discharge regulation that is conducted according to the Kama reservoir operating regulations. The simulation results of the flow velocity changes at the site Tyul’kino village – Berezniki town during different phases of water regime for high water year and average water years are presented in the article. The calculation of continuous velocity field at the site under investigation (a hydrodynamic model) is based on a digital elevation model of the bottom (DEM), and water level, water surface gradient and bottom roughness have been also considered in the model.

Numerical analysis of flow pattern transition in a conical silo with ellipsoid particles

Gravity-driven discharge flow in conical silos is ubiquitous in manufacturing processes for numerous industries such as food, pharmaceutical and chemical industries, wherein flow pattern is the key topic to be studied. In this work, discrete element method was used to study discharge flow behaviors in a special conical silo. This work aims to understand the dynamic evolution of discharge flow pattern and establish methods for regional determination of flow pattern transition. The results indicated that both mass flow and funnel flow patterns coexist in the silo at the initial stage of discharge, and there is a definite transition process from mass flow to funnel flow. Furthermore, the flow pattern transition is revealed by the change in discharge flow characteristics. Specifically, the change in force acting on particles leads to the change of particle orientation and particle velocity field, macroscopically resulting in the flow pattern transition. Finally, based on the kinetic stress field and shear rate, the height and radial region of flow pattern transition were determined, respectively. Understanding of the flow pattern transition is useful to the design, scale-up and optimization of silos and similar structural devices.

Investigation on interphase force modeling for vertical and inclined upward adiabatic bubbly flow

Modeling of interphase forces plays an important role in two-phase bubbly flow simulation. Due to the complexity of two-phase interaction, a substantial number of models have been developed. The applicability and accuracy of these models have been investigated mainly for vertical cases. Study under inclined condition can rarely be found. In the present study the characteristics of different models for interphase forces, including drag force, lift force, wall lubrication force and turbulent dispersion force, are investigated. The effects of interphase forces on the phase distribution for vertical and inclined bubbly flow are evaluated by modeling of DEDALE (Grossetete, 1995) and Xing et al. (2013) experiments. It is found that interphase forces have some different influences on the phase distribution under vertical and inclined condition. Under vertical condition large lift force can result in the high peak of void fraction, whereas under inclined condition the lift force gives the opposite effect due to the change of liquid phase velocity field. Two sets of optimal model combination are obtained by stepwise screening. For the investigated vertical cases a set of model combination including the Ishii-Zuber drag force model, Saffman-Mei lift force model, Hosokawa wall lubrication force model and FAD turbulent dispersion force model is preferable. For investigated inclined cases a set of model combination including the Simonnet drag force model, Tomiyama lift force model, Hosokawa wall lubrication force model and FAD turbulent dispersion force model is the most suitable.

Experimental Setup and Measuring System to Study Solitary Wave Interaction with Rigid Emergent Vegetation.

The aim of this study is to present a peculiar experimental setup, designed to investigate the interaction between solitary waves and rigid emergent vegetation. Flow rate changes due to the opening and closing of a software-controlled electro-valve generate a solitary wave. The complexity of the problem required the combined use of different measurement systems of water level and velocity. Preliminary results of the experimental investigation, which allow us to point out the effect of the vegetation on the propagation of a solitary wave and the effectiveness of the measuring system, are also presented. In particular, water level and velocity field changes due to the interaction of the wave with rigid vegetation are investigated in detail.

Re-establishment of ice-surface velocity field and snow surface elevation change around Dome Argus, East Antarctica

ABSTRACTIn January 2016, static GPS measurements were carried out in a 30 × 30 km2 area centered around Kunlun station at Dome Argus (Dome A), East Antarctica, to acquire high-precision 3-D geodetic coordinates at 49 sites. By comparing the coordinates with previous GPS measurements in 2008 and 2013 at the same sites, we constructed a detailed and long-term record of the ice-surface velocity field, 2008–2016, around Dome A. During this time span, the estimated ice-surface velocity ranges from 0.8 ± 0.3 to 28.7 ± 1.6 cm a−1, with a mean of 10.4 ± 0.3 cm a−1. From 2013 to 2016, the surface elevation of most Dome A areas exhibits a rising trend, and the maximum increase of snow surface elevation is 84.8 cm. The mean snow surface elevation change rate at Dome A is estimated to be 6.6 ± 0.7 cm a−1. The difference of 1.0 cm a−1 between the snow surface change rate derived from GPS and pole-height change rate from surface mass balance is suspected to be a result of a combination of firn densification and basal melt under Dome A.

Criteria for Beverlooʼs scaling law**Project supported by the National Natural Science Foundation of China (Grant Nos. 11705256 and 11605264).

Beverlooʼs scaling law can describe the flow rate of grains discharging from hoppers. In this paper, we show that the Beverlooʼs scaling law is valid for varying material parameters. The flow rates from a hopper with different hopper and orifice sizes (D, D0) are studied by running large-scale simulations. When the hopper size is fixed, the numerical results show that Beverlooʼs law is valid even if the orifice diameter is very large and then the criteria for this law are discussed. To eliminate the effect of walls, it is found that the criteria can be suggested as or . Interestingly, it is found that there is still a scaling relation between the flow rate and orifice diameter if D/D0 is fixed and less than 2. When the orifice diameter is close to the hopper size, the velocity field changes and the vertical velocities of grains above the free fall region are much larger. Then, the free fall arch assumption is invalid and Beverlooʼs law is inapplicable.

Erratum: ‘Contributions to the geomagnetic secular variation from a reanalysis of core surface dynamics’ and ‘Assimilation of ground and satellite magnetic measurements: inference of core surface magnetic and velocity field changes’

Erratum: ‘Contributions to the geomagnetic secular variation from a reanalysis of core surface dynamics’ and ‘Assimilation of ground and satellite magnetic measurements: inference of core surface magnetic and velocity field changes’

White–Metzner type viscoelastic model for cellulose nanofiber suspensions based on population balance equations for fiber floc aggregation-breakage

A viscoelastic model for cellulose nanofiber (CNF) suspensions using a population balance equation for fiber floc aggregation-breakage was proposed. A Krieger–Dougherty model was used to describe the dependence of viscosity on the volume fraction of flocs, and a White–Metzner type model was used to represent the effect of viscoelasticity. The rheological properties of the present model were investigated, and this model was confirmed to describe shear thinning in viscosity and viscoelastic responses of stress growth, depending on the relaxation time. Furthermore, flows of CNF suspensions through a circular tube were analyzed using the present model. The velocity profile changes with time according to the temporal change in the distribution of the effective volume fraction of fiber flocs. The numerical prediction of the velocity profile captures the typical properties of shear-thinning fluids. The development rate of the floc size distribution depends on the velocity gradient and affects the temporal changes of both velocity and stress fields. The development of the stress field is delayed longer for a longer relaxation time. These phenomena affect the temporal change in the floc size distribution and hence also affect the growth of the velocity field through the effective volume fraction of flocs. These results indicated that the present model can describe the viscoelastic behavior of CNF suspensions in flows.

Influence of the flow rate waveform and mass imbalance on the performance of active magnetic regenerators. Part I: Experimental analysis

This is the first part of a two-part paper on the synchronization between the applied magnetic field and fluid displacement waveforms in a gadolinium packed sphere active magnetic regenerator (AMR) apparatus. For a rectified cosine magnetic field waveform, new rotary valves were developed to assess the influence of the duration of the fluid flow steps on the AMR performance. In order to correct flow imbalance effects caused by torque oscillations in the magnetic circuit and guarantee thermodynamically consistent conditions, a new criterion based on a mass imbalance parameter has been proposed. By keeping the displaced fluid mass fixed for a given utilization, the cooling capacity increased significantly with shorter blow times due to the higher fluid velocity and larger average magnetic field change. However, because of the associated increase in power consumption, an optimal blow time fraction of 45% was identified for operating frequencies of 0.25 and 0.5 Hz.

Free-Flow Sediment Flushing: Insights from Prototype-Scale Studies

Free-flow sediment flushing operation offers viable means to preserve the storage capacity of dam reservoirs as the incoming flood erodes the flushing channel, and the deposited sediment is flushed from the reservoir. This method involves complex flow patterns and flushing channel formation procedures owing to the dynamic interaction between varying flow conditions (e.g., shallow and deep flows) and moveable bed variations notably when the non-uniform sediments exist in the complex geometry of reservoirs. In the present study, first, the numerical simulation of a previously conducted free-flow sediment flushing operation in the Dashidaira and the target segment of Unazuki reservoirs using the available field-measured data were presented. Then, to improve the flushing efficiency in the Dashidaira reservoir, the effects of using a groyne were studied. A fully 3D numerical model using the finite volume method in combination with a wetting/draying algorithm was utilized to reproduce the flow velocity field and morphological bed changes. While the characteristics of the flow field can be captured by the numerical model in Dashidaira and Unazuki reservoirs, simulated bed changes in upstream areas covered with the coarser materials (e.g., study zone of Unazuki reservoir) showed some discrepancies. The outcomes also revealed that implementing a groyne at the entrance of the wide midstream of Dashidaira reservoir can locally increase the sediment erosion chance from this area and thereby can improve the flushing efficiency by approximately 10%. Therefore, the risks associated with the accumulation of distorted sediments in the wide midstream of Dashidaira reservoir within a long-term period could be reduced.

Assimilation of ground and satellite magnetic measurements: inference of core surface magnetic and velocity field changes

Assimilation of ground and satellite magnetic measurements: inference of core surface magnetic and velocity field changes