Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   International / domestic magazine：Domestic journal  

DOI： 10.3811/jjmf.2022.012

Authorship：Corresponding author   Publishing type：Research paper (scientific journal)  

Stator coils of automobiles in operation generate heat and are cooled by coolant poured from above. The flow characteristic of the coolant depends on the coil structure, flow condition, solid–fluid interaction, and fluid property, which has not been clarified due to its complexities. Since straight coils are aligned and layered with an angle at the coolant-touchdown region, the coil structure is simplified to a horizontal square rod array referring to an actual coil size. To obtain the flow and wetting characteristics, two-phase fluid flow simulations are conducted by using the phase-field lattice Boltzmann method. First, the flow onto the single-layered rod array is discussed. The wetting area is affected both by the rod gap and the wettability, which is normalized by the gap and the averaged boundary layer thickness. Then, the flow onto the multi-layered rod arrays is investigated with different rod gaps. The top layer wetting becomes longitudinal due to the reduction of the flow advection by the second layer. The wetting area jumps up at the second layer and increases proportionally to the below layers. These become remarkable at the narrow rod gap case, and finally, the dimensionless wetting area is discussed at each layer.

DOI： 10.3390/e24020219

<p>To investigate the difference between the standard Taylor-Couette (TC) flow and axially grooved TC (GTC) flow, this study caries out DNSs of turbulent TC and GTC flow by the D3Q27 MRT lattice Boltzmann method．For the GTC flow calculated in this study，the inner rotating cylinder has no grooved and outer stationary cylinder has 24 axial grooves. From statistical results，it is found that Case GTC has a lower bulk velocity than Case TC．The kinetic energy of fluctuating velocity in Case TC has a nearly symmetric distribution，while in Case GTC，as the Reynolds number increases， the maxima are larger on the inner cylinder side than the outer cylinder side．In Case GTC，<i>Nu_ω</i> − 1，which is directly related torque，is 30% larger than the normal TC flow．This means that the torque required for rotation is increased due to the grooves．However，for the groove geometry in this study，the increase in torque is not as large as for the ribroughened TC flow in a similar study.</p>

DOI： 10.1299/jsmemecj.2022.s061p-04

Publishing type：Research paper (scientific journal)  

DOI： 10.1063/5.0058694

Authorship：Corresponding author   Publishing type：Research paper (scientific journal)  

DOI： 10.1103/physreve.103.053307

Other URL： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevE.103.053307/fulltext

Publishing type：Research paper (scientific journal)  

<jats:p> The D3Q27 lattice Boltzmann method (LBM) combined with the fluid-structure boundary reconstruction (fsBR) scheme and the interpolated bounce back (IPBB) method is extensively evaluated to predict the permeability of nonwoven fibrous porous media. The fsBR-IPBB method transfers digitally defined step-like boundary data, e.g. the three-dimensional structure data obtained by the X-ray computed tomography, to continuous smooth boundary data via level-set functions. It leads to highly accurate calculations despite low lattice resolutions of thin fibers with circular cross-sectional shapes, compared to the conventional half-way bounce back (HWBB) method. The fsBR-IPBB method is first applied to predict the permeability of two different arrays of impermeable circular cylinders and verified by comparing the results with the data in the literature. We then validate the method referring to the numerically and experimentally obtained permeability of six types of nonwoven fabrics prepared by the industrial hydroentanglement process. Finally, the discussion on the applicability and the limitation of the macroscopic correlation models to estimate permeability of porous media is carried out. The results show that although the calculated permeability is in reasonable agreement with the measured one with an error of 8.1–16.3%, analytical or empirical correlation models fail to give the correct trend due to the highly inhomogeneous and anisotropic properties of hydroentangled nonwoven fabrics. </jats:p>

DOI： 10.1177/1528083720978913

Kind of work：Joint Work  

Kind of work：Joint Work  

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)  

© 2020 Elsevier B.V. The natural convection of a paramagnetic fluid is numerically investigated in the presence of a magnetic field from a block permanent magnet. One vertical wall of a cavity is partially heated at a constant heat flux to consider a single vertical heated wall. The permanent block magnet is placed behind the heated wall, of which the magnetic field is numerically obtained. Since the magnetic force is remarkable at edges of the block magnet, the magnetothermal force is also pronounced if the temperature difference exists by wall heating. The overlapping magnetothermal force works to repel the fluid. This results in the heat transfer enhancement near the upper magnet edge, and suppression near the lower magnet edge. The suppressing effect becomes remarkable rather than the enhancing one in cases of large magnetic induction, high wall heat flux, and high magnet elevation to the heated wall.

DOI： 10.1016/j.jmmm.2020.166574

Kind of work：Joint Work  

Repository URL： http://hdl.handle.net/10466/00017054

Authorship：Corresponding author   Publishing type：Research paper (scientific journal)  

© 2020 by the authors. The convection control is important in terms of the heat transfer enhancement and improvement of the applied devices and resultant products. In this study, the convection control by a magnetic field from block permanent magnets is numerically investigated on the Rayleigh-Benard convection of paramagnetic fluid. To enhance the magnetic force from the available permanent magnets, pairs of alternating-pole magnets are employed and aligned near the bottom heated wall. The lattice Boltzmann method is employed for the computation of the heat and fluid flow with the consideration of buoyancy and magnetothermal force on the working fluid. It is found that, since the magnetic force at the junction of pair magnets becomes strong remarkably and in the same direction as the gravity, descending convection flow is locally enhanced and the pair of symmetrical roll cells near the magnet junction becomes longitudinal. The local heat transfer corresponds to the aected roll cell pattern; locally enhanced at the magnet junctions and low heat transfer area is shifted aside the magnet outer edge. The averaged Nusselt number on the hot wall also increases proportionally to the magnetic induction but it is saturated at high magnetic induction. This suggests the roll cell pattern is no more largely aected at extremely-high magnetic induction.

DOI： 10.3390/sym12030341

Kind of work：Joint Work  

Kind of work：Joint Work  

Publishing type：Research paper (international conference proceedings)  

Copyright © ETC 2013 - 14th European Turbulence Conference.All rights reserved. In order to understand the effects of the wall permeability on turbulence near permeable walls, spanwise flow field measurements are carried out for turbulent flows in channels with permeable bottom walls by a two-component particle velocimetry (PIV) system. The porous media used are three kinds of foamed ceramics which have almost the same porosity (∼ 0.8) but different permeability. The turbulent flow fields in the spanwise planes are discussed using instantaneous and statistical measurement data. At a small permeability Re (ReK), low speed and high speed regions, which form a similar streaky structure to that of solid-wall turbulence, are observed. In case of a large ReK, although some large scale striped patterns are observed, they are confirmed to be different from those of the solid wall turbulence structure.

Authorship：Corresponding author   Publishing type：Research paper (scientific journal)  

© 2020 The Japan Society of Mechanical Engineers. Natural convection of a paramagnetic fluid through a partially-heated vertical channel is numerically studied in the presence of a magnetic field from two block magnets placed behind the heated wall. Magnets are aligned with opposite orientations. This magnet orientation induces strong magnetic force normal to the magnet at the magnet junction due to short distance between poles. When the temperature-dependent magnetic susceptibility changes due to wall heating near the magnet, the magnetothermal force is induced remarkably near the magnet junction. This additional force overlaps to the natural convection along the heated wall and results in the changes of heat and fluid flow along the heated wall. It is found that, flow becomes slow and the local heat transfer is suppressed below the elevation of the magnet junction, and the flow acceleration and heat transfer enhancement are observed above the junction elevation, of which effects depend on the relative magnet elevation to the heated wall. It is also found that the transition to vibrating flow occurs at the specific magnet elevation. The time-averaged Nusselt number suggests this vibrating convection has the potential to enhance the heat transfer remarkably because this magnetically-induced flow vibration continues along the heated wall up to the outlet.

DOI： 10.1299/jtst.2020jtst0019

Authorship：Corresponding author  

<p>Imbibition of single droplet onto porous surface can be observed in engineering devices such as the oil mist filter, inkjet printings, etc. This two-phase flow is governed by physical properties of liquid and porous media. When the droplet size is comparable to the pore scale, the droplet behavior additionally depends on the structural characteristics of the porous media, which has not been clarified yet. It requires to consider not only the physical properties of two-phase flow but also the solid structure. We employed the phase-field lattice Boltzmann method (PFLBM) to compute the two-phase flow on the complicated structures. Since the conventional PFLBM has less precision in the solid representation, wettability and the phase volume consideration on curved boundaries, we improved this method by employing hybrid interpolated bounce-back scheme in the three dimensional system with considering wall normal direction geometrically. It shows the reasonable droplet behavior on a flat plate inclined from the grid line. A static droplet on a sphere is represented by the reasonable position and shape of the contact line. The phase-volume error derived from the conventional interpolated bounce-back is successfully suppressed. Next, the characteristic of the droplet entrapment and/or infiltration by isotropic open cell (Kelvin cell) porous media is numerically studied. It is found that the threshold wettability exists between entrapment and infiltration regardless of the surface topology of the porous media. As the droplet size becomes smaller, the effect of the porous surface becomes remarkable in the threshold contact angle and infiltration ratio at higher contact angle. In case of the droplet entrapment above the porous surface, the lyophobicity of the porous surface becomes remarkable, which merges to the given contact angle at the super-lyophobicity due to the less wetted ligaments.</p>

DOI： 10.1299/transjsme.20-00014

CiNii Article

Kind of work：Joint Work  

Repository URL： http://hdl.handle.net/10466/16196

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Presentation type：Poster presentation  

Venue：富山  

Presentation type：Oral presentation (general)  

Venue：オンライン  

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Venue：秋田  

Presentation type：Oral presentation (general)  

Venue：岐阜  

Presentation type：Oral presentation (invited, special)  

Presentation type：Oral presentation (general)  

Venue：オンライン  

Presentation type：Poster presentation  

Presentation type：Poster presentation  

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Original item：JHPCN 学際大規模情報基盤共同利用採択