SEISAN KENKYU
Online ISSN : 1881-2058
Print ISSN : 0037-105X
ISSN-L : 0037-105X
Volume 71 , Issue 1
Showing 1-13 articles out of 13 articles from the selected issue
Preface
Introduction to Special Section
Research Flash
  • Fujihiro HAMBA
    2019 Volume 71 Issue 1 Pages 5-8
    Published: January 01, 2019
    Released: January 31, 2019
    JOURNAL FREE ACCESS

    The energy transport in the scale space in turbulent channel flow was examined to show that the inverse cascade is seen in the spanwise part of turbulent energy. In order to understand the flow structure associated with the inverse cascade, the conditional average of velocity field was evaluated in relation to the negative energy production. The profiles of the conditional average showed that the two streamwise vortices are seen near the region of the negative production. The downward flow impinging toward the wall enhances the spanwise grid-scale velocity components, resulting in the inverse cascade of the spanwise energy.

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  • Nobumitsu YOKOI, Valera TITOV, Rodion STEPANOV, Mahendra VERMA, Ravi S ...
    2019 Volume 71 Issue 1 Pages 9-13
    Published: January 01, 2019
    Released: January 31, 2019
    JOURNAL FREE ACCESS

    We perform direct numerical simulations of magnetohydrodynamic (MHD) turbulence with kinetic energy and cross helicity injections at large scales. We observe that the cross helicity changes sign as we go from large and intermediate scales to small scales. In addition, the magnetic reconnections are strongest at the regions where the cross helicity changes sign and becomes smallest in magnitude. Thus, our simulations provide an important window to explore the regions of magnetic reconnections in nonlinear MHD.

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  • Kazuhiro INAGAKI, Fujihiro HAMBA
    2019 Volume 71 Issue 1 Pages 15-18
    Published: January 01, 2019
    Released: January 31, 2019
    JOURNAL FREE ACCESS

    For rotating inhomogeneous turbulence accompanied with helicity, it was numerically shown that axial mean velocity is generated and sustained. The previous study showed that the pressure diffusion term is a leading candidate for the source of the Reynolds shear stress which induces the axial mean velocity. In this study, discussion is given on the role of another contribution due to the rotation, the Coriolis effect term. Numerical study suggests that the Coriolis effect term does not grow while the axial mean velocity and the Reynolds shear stress are generated. Moreover, it is suggested that the previous turbulence models cannot explain the numerically observed spatial distribution of the Coriolis effect term.

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  • Jinxin ZHOU, Sanggyu PARK, Takero YOSHIDA, Qiao LI, Junbo ZHANG, Daisu ...
    2019 Volume 71 Issue 1 Pages 19-22
    Published: January 01, 2019
    Released: January 31, 2019
    JOURNAL FREE ACCESS

    The physical environment of Miho Bay was simulated to investigate the variations in water current and water temperature around the aquaculture site. According to the comparison of observed and simulated current velocities, it was suggested that the wind-driven current is the major current in the bay. As future studies, meteorological condition should be given more precisely. Then the river inflow and the water exchange between Naka-umi and Miho Bay should be taken into account. The water current and quality fields around cages will be simulated in detail using a nested grid system, combining the lower-trophic ecosystem model.

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Research Review
  • Mengtao HAN, Ryozo OOKA, Hideki KIKUMOTO
    2019 Volume 71 Issue 1 Pages 23-28
    Published: January 01, 2019
    Released: January 31, 2019
    JOURNAL FREE ACCESS

    In recent years, Lattice Boltzmann method (LBM), has been applied in built wind simulation. In this study, LBM assembled with large-eddy simulation (LBM-LES) were employed, as well as the finite volume method (FVM-LES), to simulate an indoor isothermal forced convection case, aiming to verify the prediction accuracy of LBM-LES method, and to compare their results accuracy and computational speeds. The result shows that LBM-LES method can acquire FVM-LES’ precision in predicting indoor turbulent flow, however it required finer meshes. In the aspect of computational speed, LBM-LES expressed better parallel computational efficiency, especially when using more computational cores, the computational speed of LBM-LES became larger than that of FVM-LES in the case of the same results accuracy.

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  • Chao LIN, Ryozo OOKA, Hideki KIKUMOTO, Taiki SATO
    2019 Volume 71 Issue 1 Pages 29-34
    Published: January 01, 2019
    Released: January 31, 2019
    JOURNAL FREE ACCESS

    Extremely high temperature exhaust gases are emitted around the building during operation of the boiler and generator. In order to analyze the influence on people’s safety and building surfaces and devise appropriate countermeasures, it is necessary to predict the dispersion in advance. In this study, with respect to the dispersion prediction of high temperature exhaust gases around the isolated building, the CFD reproduction analysis of the existing wind tunnel experiments and the prediction analysis of higher buoyancy were conducted by using weakly compressible k-ε model and incompressible k-ε model. In the high concentration region near the exhaust vent, the weakly compressible model showed a higher value. Here the difference between the two models are discussed in the aspect of buoyant acceleration and production and dissipation of turbulence kinetic energy.

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Research Flash
  • Shan GAO, Qianwen GUO, Ryozo OOKA, Wonseok OH
    2019 Volume 71 Issue 1 Pages 35-39
    Published: January 01, 2019
    Released: January 31, 2019
    JOURNAL FREE ACCESS

    In the radiation air conditioning system, non-uniformity of the indoor thermal environment may occur depending on the installation position of the radiation panel. In this research, in order to investigate discomfort due to this asymmetric thermal radiation, numerical analysis was performed by heating one of the wall surfacesAs the case of the uniform thermal environment, the convective heat transfer coefficient of the human limbs was larger than the trunk, and the radiation heat transfer coefficient was reversed.

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  • Yang GUO, Chisachi KATO, Yoshinobu YAMADE
    2019 Volume 71 Issue 1 Pages 41-45
    Published: January 01, 2019
    Released: January 31, 2019
    JOURNAL FREE ACCESS

    A compressible flow solver using the finite element method was developed. Three benchmark test cases were validated: lid-driving cavity flow, laminar flow around a square cylinder and turbulent flow around a NACA0012 airfoil. In the lid-driving cavity flow, the mean velocity profiles at sampling lines agree well with the experimental data. In the laminar flow around a square cylinder, the normalized r.m.s. pressure along a sampling line agrees reasonably well with the theoretical solution. In the turbulent flow around NACA0012

    airfoil, the mean pressure coefficient, r.m.s. pressure coefficient and the mean velocity profiles in the turbulent boundary layer agree fairly well with the experimental one.

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  • Shunsei TANAKA, Yuya SAKAI
    2019 Volume 71 Issue 1 Pages 47-50
    Published: January 01, 2019
    Released: January 31, 2019
    JOURNAL FREE ACCESS

    A method for measuring the carbonation depth by observation with a fiber scope was proposed. It was confirmed that the coloration by phenolphthalein solution on the wall surface of a 1 mm drill hole can be clearly observed with a 0.6 mm fiberscope. In addition, a method for determining the distance from the end of the fiber scope to the object was examined. Then the proposed method was applied to a concrete specimen and a mortar specimen. Comparison with the results of measurements with the cut surface showed that the proposed method has good accuracy.

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  • Yoko ITO, Yuya SAKAI, Rie MAKIURA
    2019 Volume 71 Issue 1 Pages 51-54
    Published: January 01, 2019
    Released: January 31, 2019
    JOURNAL FREE ACCESS

    This study analyzes the water-retaining mechanism of surfactant-based curing agents. Curing agents on the water surface were observed with the help of a Brewster angle microscope, which is often employed for studying ultrathin films on liquid surfaces. Curing agents of various concentrations were prepared and instilled into pure water. The resulting surfactant effect on the water surface was subsequently observed. When a curing agent with concentration lower than 10% was instilled, the film spread over the water surface. However, when a curing agent with concentration higher than 17% was instilled, several lumps formed instead of a film, which primarily indicates aggregated surfactants. The film-forming process observed in this study indicates that curing agents having low concentrations can significantly suppress the rate of water evaporation.

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  • Yuya SAKAI, Yoichi FUNABIKI, Yukiya WATANABE
    2019 Volume 71 Issue 1 Pages 55-58
    Published: January 01, 2019
    Released: January 31, 2019
    JOURNAL FREE ACCESS

    Electron backscatter diffraction analysis was conducted on hardened cement paste. The inverse pole figure maps of Ca(OH)2 and CaCO3 were almost black, indicating that the crystal orientation was not identified.The same observation was made with cement clinkers. These results indicate that the crystal structure of the hydrates in hardened cement paste and cement clinkers varies widely and is different from the standard crystal structures. The distribution of hydrates with different crystallinity was successfully visualized in image quality maps.

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