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Numerical Simulation of Droplet-Formation in Rotary Atomizer

Naoki Igari, Takuro Iso, Yu Nishio, Seiichiro Izawa, Yu Fukunishi

Accepted Manuscript

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Abstract:
Numerical simulations of the liquid flow scattering from rotary atomizers are performed using an incompressible smoothed particle hydrodynamics (SPH) method. The influence of grooves at the edges of the atomizers on the formation of ligaments and droplets is investigated changing the numbers and shapes of the grooves. As a result, it is found that small droplets are likely to be generated when the number of grooves is large and the depth of grooves is deep. It is also found that the grooves work more effectively in bell-cup atomizers than in disk type atomizers.

Torsional Negative Stiffness Mechanism by Thin Strips

Jinyou Li, Kangjia Fu, Yongpeng Gu, Zhihua Zhao

Accepted Manuscript

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Abstract:
Negative stiffness mechanisms have great application potential in different fields, such as vibration isolation, energy absorption and mesh antenna unfolding. Although numerous compliant mechanisms with negative stiffness features have been implemented in literature, the designing work remains in its infancy, and proposing an original design strategy may open a new avenue for the future inventions. In this study, inspired by a toy, we developed a novel type of compliant mechanism composed of thin strips, possessing negative stiffness property under torsion. The negative stiffness feature is achieved by large deformation of the strips rather than mechanical buckling. As a consequence, the obtained negative stiffness segment covers a significantly long range. Demonstrated with examples, it was shown that the proposed mechanisms could be combined with other compliant mechanisms to realize long-range abnormal torque-angle relationships, which can be used in different applications.

Progress on design and related R&D activities for the water-cooled breeder blanket for CFETR

Songlin Liu, Xiaoman Cheng, Xuebin Ma, Lei Chen, Kecheng Jiang, Xia Li, Hui Bao, Jichao Wang, Wanjing Wang, Changhong Peng, Peng Lu, Min Li, Kai Huang

Uncorrected proof , doi: 10.1016/j.taml.2019.03.001

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Abstract:
The water-cooled ceramic breeder (WCCB) blanket is one of the blanket candidates for Chinese fusion engineering testing reactor (CFETR) and is being developed at the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP). This paper reviews design and evolution of the WCCB blanket for CFETR, and presents a new WCCB blanket design according to the latest CFETR core parameters (major/minor radius is R = 7.2 m, a = 2.2 m) and missions. This new design is expected to satisfy multiple CFETR operation modes of 200 MW, 500 MW, 1 GW, and 1.5 GW fusion power and achieve tritium self-sufficiency. The feasibility of the updated blanket design is evaluated from the aspects of neutronics and thermo-hydraulics. Furthermore, the R&D activities supporting to the WCCB blanket for CFETR are reported, including the design code, the water loop experiments, the pebble bed modeling and experiments, and the components fabrication technology.

Numerical analysis of a simplest fractional-order hyperchaotic system

Dong Peng, Kehui Sun, Shaobo He, Limin Zhang, Abdulaziz O. A. Alamodi

Uncorrected proof , doi: 10.1016/j.taml.2019.03.006

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Abstract:
In this paper, a simplest fractional-order hyperchaotic (SFOH) system is obtained when the fractional calculus is applied to the piecewise-linear hyperchaotic system, which possesses seven terms without any quadratic or higher-order polynomials. The numerical solution of the SFOH system is investigated based on the Adomian decomposition method (ADM). The methods of segmentation and replacement function are proposed to solve this system and analyze the dynamics. Dynamics of this system are demonstrated by means of phase portraits, bifurcation diagrams, Lyapunov exponent spectrum (LEs) and Poincaré section. The results show that the system has a wide chaotic range with order change, and large Lyapunov exponent when the order is very small, which indicates that the system has a good application prospect. Besides, the parameter a is a partial amplitude controller for the SFOH system. Finally, the system is successfully implemented by digital signal processor (DSP). It lays a foundation for the application of the SFOH system.

Preferential orientation of tracer spheroids in turbulent channel flow

Yucheng Jie, Lihao Zhao, Chunxiao Xu, Helge I. Andersson

Uncorrected proof , doi: 10.1016/j.taml.2019.03.010

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Abstract:
Axis-symmetric spheroids, such as rod-like and disk-like particles, have been found to orient preferentially in near-wall turbulence by both experiment and numerical simulation. In current work we examined the orientation of inertialess spheroids in a turbulent channel flow at medium friction Reynolds

\begin{document}${{{ Re}} _{\rm{\tau }}} = 1000$\end{document}

given based on the half of channel height. Both elongated prolate spheroid and flat oblate spheroid are considered and further compared with the reference case of spherical particle. The statistical results show that in near wall region the prolate spheroids tend to align in the streamwise direction while the oblate spheroids prefer to orient in the wall-normal direction, which are consistent with earlier observation in low Reynolds number (

\begin{document}${{\mathop{\rm Re}\nolimits} _{\rm{\tau }}} = 180$\end{document}

) wall turbulence. Around the channel center we found that the orientation of spheroids is not fully isotropic, even though the fluid vorticity are almost isotropic. The mechanism that gives rise to such particle orientations in wall-turbulence has been found to be related to fluid Lagrangian stretching and compression (Zhao and Andersson 2016). Therefore, we computed the left Cauchy-Green strain tensor along Lagrangian trajectories of tracer spheroids in current flow field and analyzed the fluid Lagrangian stretching and compression. The results indicated that, similar to the earlier observations, the directions of the Lagrangian stretching and compression in near-wall region are in the streamwise and wall-normal directions, respectively. Furthermore, cross over the channel the prolate spheroids aligned with the direction of Lagrangian stretching but oblate spheroids oriented with the direction of Lagrangian compression. The weak anisotropy of orientations of fluid Lagrangian stretching and compression observed at the channel center could be the reason for the aforementioned modest anisotropic orientation of spheroids in channel central region.

Heat transfer performance for DCLL blanket with no-wetting insulator walls

Hulin Huang, Shimou Yin, Guiping Zhu

Uncorrected proof

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Abstract:
Magnetohydrodynamic (MHD) effect and heat transfer are two key issues for design of dual coolant lead lithium (DCLL) blanket. Flow channel insert (FCI) has been applied to decouple the liquid metal from the walls to efficiently decline MHD pressure drops and reduce heat losses from the liquid metal for increasing bulk exit temperatures of the blanket. However, there are still big pressure drops and a higher velocity jet located at the gap flow. Moreover, the FCI made from silicon carbide (SiC) constitutes a complex blanket structures which potentially causes special flow phenomena. In the present work, the characteristics of fluid flow and heat transfer in the DCLL blanket channel are investigated for the first wall (FW) sprayed a layer of no-wetting nano coating (NWNC) on its inner surface. The results show that the pressure drop with NWNC wall is one-order magnitude lower than that with flow channel insert (FCI) in the general DCLL blanket. The Nusselt number on the NWNC wall is about half of that on the general wall. On this basis, a heat transfer criterion equation of DCLL channel is achieved for the NWNC wall without FCI. The results are compared with that criterion equation of general wall conditions, which indicates the criterion equation can well predict the convection heat transfer of DCLL channel.

Delamination strength of HTS tape under transverse tensile stress and its enhancement by using different Ag layer depositing temperatures

Jun Wang, Ce Sun, Liu Cong, Xingyi Zhang, Youhe Zhou

Uncorrected proof , doi: 10.1016/j.taml.2019.03.002

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Abstract:
For the application of second generation high temperature superconducting coated conductors (CCs) with layered structures, thermal mismatch between different components and electro-magnetic force exerted in superconducting layer in a working magnet can cause transverse tensile stress, which would result in delamination behavior. Therefore many research groups have designed experiments to measure the delamination strength and dedicate to improving that. However, the reason of the discrete distribution of measured data has still not get quantitatively studied, besides, there are lack of investigations on the method of changing depositing conditions to improve the delamination strength except by adding an additional metal layer. In this work, we adopt an anvil test device and obtain delamination strengths as 29.6 MPa of YBa₂Cu₃O_7−x (YBCO)/buffer and 114.6 MPa of buffer/substrate by combing energy disperse spectroscopy (EDS) detection. The reason of discretized measurement data on the delamination strength is explained. Moreover, we find that different temperatures during Ag deposition determine the bonding force of Ag and YBCO layer. The Delamination strength between Ag and YBCO layer increases from 4.4 MPa to larger than 114.6 MPa with temperature elevated from 30 °C to 100 °C. Hence we present a novel method for improving the delamination strength of YBCO CCs by setting an optimal temperature of Ag deposition.

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Letter

Particle selectivity of filtering by C. elegans

Yuki Suzuki, Kenji Kikuchi, Keiko Tsuruta-Numayama, Takuji Ishikawa

2019, 9(2): 61 -65. doi: 10.1016/j.taml.2019.02.001

[Abstract] (21) [FullText HTML] (9) [PDF 2867KB] (4)

Abstract:
A nematode Caenorhabditis elegans (C. elegans) is a filter feeder, which draws a suspension of bacteria and separates bacteria from the solvent by using pharyngeal pumping motions and specific mouth parts. This mechanism has not been fully understood. We investigated the mechanism of filtering of bacteria in the pharynx of C. elegans by visualization by fluorescent particles and dyed E. coli. We succeeded in quantifying the selectivity of bacteria-sized particles by C. elegans. The most accumulated particles were those of 0.5 μm in diameter. The quantity of accumulated particles of 0.2 μm or 1.0 μm in diameter was about one third of that of particles of 0.5 μm in diameter. The least accumulated particles were those of 0.05 μm in diameter. These results suggest that the pharyngeal structures of C. elegans would be suitable for eating bacteria because the size of bacteria ingested by C. elegans worms is about 0.5 μm in diameter. We also succeeded in visualizing pharyngeal structures and pumping motions and flow in the pharynx. We found that there were phase differences in the motions among procorpus, metacorpus and isthmus. This result suggests filtering would occur at the two tips of procorpus and isthmus by the phase differences. We found that bacteria-sized particles and bacteria were flowed and trapped in the channels, which existed along the central lumen from tip of procorpus to isthmus. From our results, we proposed the novel mechanism of filtering of bacteria through the channels for flowing and trapping. In future, this selective filtering mechanism of C. elegans would be applied to development of microfluidic filtration devices for medical and biological equipment.

The extractable hydrokinetic power from an oscillating membrane-based harvester

Francisco J. Arias, Salvador De Las Heras

2019, 9(2): 66 -70. doi: 10.1016/j.taml.2019.01.003

[Abstract] (70) [FullText HTML] (32) [PDF 2733KB] (13)

Abstract:
The extractable hydrokinetic power from an oscillating membrane in standing motion and induced by a water flow and its possible significance with regard energy harvesting is discussed. The main attractiveness of such an energy harvester lies in the possibility of an inexpensive technology able to be used in those water flows which either because limitation of space (narrow channels) or a limited differential pressure drop with the surrounding but yet with a non negligible velocity are not well suited to be turbined. Utilizing a simplified geometrical model, an estimate of the extractable output density power per area of membrane was derived. Preliminary experiments were performed using a rectangular thin rubber membrane and for a typical domestic water intake as source. The experimental data quantitatively agree very well with the theoretical prediction where it was found that for water flows around 2 m/s the output power density from the membrane may be around 30 mW/cm² of membrane. Additional research and development is required in order to arrive at a reliable practical and commercial design.

Impact of spray droplets on momentum and heat transport in a turbulent marine atmospheric boundary layer

Ming Pan, Caixi Liu, Qingxiang Li, Shuai Tang, Lian Shen, Yuhong Dong

2019, 9(2): 71 -78. doi: 10.1016/j.taml.2019.02.002

[Abstract] (56) [FullText HTML] (19) [PDF 2862KB] (6)

Abstract:
Droplet-laden turbulent airflow (i.e. the mixture of dry air and water vapor) in the marine atmospheric boundary layer is described by an open channel flow configuration in direct numerical simulation (DNS). The dispersed phase, the spray droplets are tracked in a Lagrangian framework, and their impact on the carrier airflow is modeled with the two-way coupling between the two phases. A wide-range droplet size is typically found near the air–sea interface according to the sea spray concentration function (SSCF). The interactions of the droplets with turbulent airflow including mass, momentum, and energy exchange are investigated here. We found a balancing mechanism exists in the droplet effects on the turbulent drag coefficient, since spray droplets lead to a decreased vertical turbulent momentum transport, but also lead to an increased droplet contribution to total drag coefficient. For the heat transfer, as droplet mass loading increasing, the total Nusselt number decreases due to the depression of turbulent heat flux and enhanced negative droplet convective flux.

A new numerical framework for large-eddy simulation of waves generated by objects piercing water surface

Zixuan Yang, Zuo Cui, Shizhao Wang

2019, 9(2): 79 -83. doi: 10.1016/j.taml.2019.02.003

[Abstract] (89) [FullText HTML] (32) [PDF 2560KB] (8)

Abstract:
A novel numerical framework is developed for large-eddy simulation (LES) of interactions among air, water, and solid bodies. The motions of air and water are solved on a fixed block-structured mesh, with the air–water interface captured using the volume-of-fluid method. A new sub-grid scale stress model based on the vortex identifier is used to improve the robustness and efficiency of the simulation flows with air–water interface. The new framework is tested in the context of bow waves and Kelvin waves generated by a water-surface vehicle. Wave breaking at the bow of the vehicle is captured in LES. The LES results of wave geometry approaches the measurements progressively as the grid resolution is refined. The simulation results indicate that LES is a useful tool for studying wave dynamics of water-surface vehicles.

Marangoni liquid film scattering over an extending cylinder

Taza Gul, M. Sohail

2019, 9(2): 106 -112. doi: 10.1016/j.taml.2019.02.010

[Abstract] (40) [FullText HTML] (14) [PDF 3129KB] (3)

Abstract:
The impact of the Marangoni convection over the thin film flow on an expanding cylinder has been examined in this study. The diverse effect of the embedded constraints has been detected during the liquid film flow. It has been examined that the behavior of the physical parameters altered after the small intervals and diverse from the traditional approach. The similarity variables have been utilized to alter the basic flow equations into the nonlinear ordinary differential equations. The result of the transformed equations is computed by BVPh 2.0 package. The performance of different constraints, for flow motion and temperature distributions are plotted and conferred. It has been observed that under the Marangoni convection the impact of the physical parameters varies after the point of inflection and the diverse impact of the embedding constraints provide space for the variation of the point of inflection for the desired spray analysis.

On the thixotropic effect of turbulence

Yu-Ning Huang

2019, 9(2): 113 -119. doi: 10.1016/j.taml.2019.02.007

[Abstract] (59) [FullText HTML] (24) [PDF 2499KB] (9)

Abstract:
As a follow-up research of the work on the natural viscosity of turbulence of Huang et al. [Journal of Turbulence (2003)], here we investigate the thixotropic effect of a turbulent Newtonian fluid on the basis of the ensemble-averaged Navier–Stokes equation. In view of the natural viscosity, we show that in homogeneous isotropic turbulence the turbulent Newtonian fluid behaves like a thixotropic fluid, exhibiting the thixotropic effect with its natural viscosity decreasing with time.

Research on vacuum drying process and internal heat conduction of Li-ion battery core

Zhao Jiang, Fanghua Zhao, Yuming Guan, Zizhen Qiu

2019, 9(2): 120 -129. doi: 10.1016/j.taml.2019.02.008

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Abstract:
In this research, an innovative cylindrical automatic battery core oven was designed to avoid the structural deformation that frequently occurs in traditional ovens. The oven could be automatically connected with the electrolyte injection process after baking, achieving improvement in a battery's baking consistency. This contributed to the feasibility of studying the internal heat conduction process of batch battery cores during actual baking processes. A mathematical model of a certain plate battery cell during the baking process was established. The simulation results of the temperature change inside the battery core during the baking process were consistent with the calculation results of the mathematical model. The temperature distribution at each point inside the battery core could be fitted through the thermal conductivity at different temperatures and the temperature distribution between the layers of the battery core. Finally, based on the thermodynamic balance energy conservation method, the relationship between the temperature change inside the battery core and the entire baking process was established. A feasible algorithm for studying the thermal conduction of complex material and internal structure objects in the baking process was obtained.

Article

Numerical solutions for point masses sliding over analytical surfaces: Part 1

Glauco Gallotti, Stefano Tinti

2019, 9(2): 84 -95. doi: 10.1016/j.taml.2019.02.004

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Abstract:
In this study, we introduce a system of differential equations describing the motion of a single point mass or of two interacting point masses on a surface, that is solved by a fourth-order explicit Runge–Kutta (RK4) scheme. The forces acting on the masses are gravity, the reaction force of the surface, friction, and, in case of two masses, their mutual interaction force. This latter is introduced by imposing that the geometrical distance between the coupled masses is constant. The solution is computed under the assumption that the point masses strictly slide on the surface, without leaping or rolling. To avoid complications stemming from numerical errors related to real topographies that are only known over discrete grids, we restrict our attention to simulations on analytical continuous surfaces. This study sets the basis for a generalization to more complex systems of masses, such as chains or matrices of blocks that are often used to model complex processes such as landslides and rockfalls. The results shown in this paper provide a background for a companion paper in which the system of equations is generalized, and different geometries are presented.

Article

Numerical solutions for point masses sliding over analytical surfaces: Part 2

Stefano Tinti, Glauco Gallotti

2019, 9(2): 96 -105. doi: 10.1016/j.taml.2019.02.005

[Abstract] (42) [FullText HTML] (19) [PDF 3067KB] (4)

Abstract:
This paper is the second of two companion papers addressing the dynamics of two coupled masses sliding on analytical surfaces and interacting with one another. The motion occurs under the effect of gravity, the reaction force of the surface and basal friction. The interaction force maintains the masses at a fixed distance and lies on the line connecting them. The equations of motion form a system of ordinary differential equations that are solved through a fourth-order Runge–Kutta numerical scheme. In the first paper we considered an approximate method holding when the line joining the masses is almost tangent to the surface at the instant mass positions. In this second paper we provide a general solution. Firstly, we present special cases in which the system has exact solutions. Second, we consider a series of numerical examples where the interest is focused on the trajectories of the masses and on the intensity and changes of the interaction force.

Air-vent layouts and water-air flow behaviors of a wide spillway aerator

James Yang, Penghua Teng, Chang Lin

2019, 9(2): 130 -143. doi: 10.1016/j.taml.2019.02.009

[Abstract] (27) [FullText HTML] (10) [PDF 3831KB] (2)

Abstract:
A spillway aerator should guarantee favorable flow conditions in the coupled water-air system even if the aerator is unconventionally wide. Eight air-vent configurations are devised and incorporated into a 35-m wide chute aerator for a generalized study. Computational fluid dynamics (CFD) simulations are performed to explore their effects on water-jet and air-cavity features. The Re-normalisation group (RNG)

\begin{document}$k - \varepsilon $\end{document}

turbulence model and the two-fluid model are combined to predict the two-phase flow field. The results demonstrate appreciable influences of the vent layouts on the water-air flow. The air vents stir the air motion and re-distribute the cavity air pressure. Once the vent layout is modified, reciprocal adjustments exist between the jet behavior and air-pressure field in the cavity, thus leading to considerable differences in air-flow rate, jet-trajectory length, vent air-flow distribution across the chute, etc. The large width plays a discernable role in affecting the aerated flow. Telling differences exist between the near-wall region and the central part of the chute. To improve the duct pressure propagation, a gradual augment of the vent area should be assigned towards the chute center. Relative to single-slot vents across the flow, the layouts with segregated vents gain by comparison. A designer should see to it that a vented aerator operates satisfactorily for a given range of flow discharges.