SEISAN KENKYU
Online ISSN : 1881-2058
Print ISSN : 0037-105X
ISSN-L : 0037-105X
Volume 72 , Issue 1
Showing 1-17 articles out of 17 articles from the selected issue
Preface
Introduction to Special Section
Research Flash
  • Zhuchen LIU, Yosuke HASEGAWA
    Type: Research Flash
    2020 Volume 72 Issue 1 Pages 5-8
    Published: January 01, 2020
    Released: January 31, 2020
    JOURNAL FREE ACCESS

    The present study aims at estimating the state of wall turbulence with wall information only.

    Specifically, based on wall shear stresses and wall pressure, the instantaneous state of a fully developed turbulent channel flow is estimated. As a result, it is found that the past and future measurements drastically improve the estimation performance for a large-scale structure. Among them, the past measurement is found to have a larger impact on the estimation performance, and this is related to the fact that the near-wall fluid is transferred toward away from the wall due to ejection events.

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  • Toshitaka ITOH, Yosuke HASEGAWA
    Type: Research Flash
    2020 Volume 72 Issue 1 Pages 9-13
    Published: January 01, 2020
    Released: January 31, 2020
    JOURNAL FREE ACCESS

    Aiming at the development of a better open-loop turbulence control strategy, large-scale wall transpiration is optimized so as to suppresses turbulent kinetic energy in a fully developed channel flow. High-wavenumber control inputs are constrained by adding a penalty term in the cost functional. It is shown that more than 17% drag reduction can be achieved even under the strong constraint of uniformity in the streamwise or spanwise direction.

    Further analyses suggest different mechanisms of drag reduction for each controlled case.

    Finally, we apply the obtained large-scale optimal input as an open-loop control, and confirm the temporary reduction of the turbulent kinetic energy after the onset of the control.

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  • Arjun J. KAITHAKKAL, Yukinori KAMETANI, Yosuke HASEGAWA
    Type: Research Flash
    2020 Volume 72 Issue 1 Pages 15-18
    Published: January 01, 2020
    Released: January 31, 2020
    JOURNAL FREE ACCESS

    The present work analyses heat transfer mechanisms in a turbulent channel flow subjected to a traveling wave-like wall blowing and suction. Due to the coherent nature of the control input, turbulence fluctuations are decomposed into its coherent and random components.

    The budget analysis of their contributions to dissimilar heat transfer enhancement identifies the two key factors generating the dissimilarity. It is shown that the random contribution is dominant, and mainly caused by the indirect interaction between the coherent and random fields.

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  • Fujihiro HAMBA
    Type: Research Flash
    2020 Volume 72 Issue 1 Pages 19-23
    Published: January 01, 2020
    Released: January 31, 2020
    JOURNAL FREE ACCESS

    The energy transport in the scale space in turbulent channel flow was examined to show that an inverse cascade can be seen in part of turbulent energy. In order to understand flow structures associated with the inverse cascade, the conditional average of velocity field was evaluated in relation to the negative value of the energy production term. Profiles of the conditional average showed that vortices are seen near the region of the negative production. A downward flow impinging toward the wall enhances the grid-scale velocity component along the wall, resulting in the inverse cascade of the energy.

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  • Nobumitsu YOKOI
    Type: Research Flash
    2020 Volume 72 Issue 1 Pages 25-29
    Published: January 01, 2020
    Released: January 31, 2020
    JOURNAL FREE ACCESS

    Results of analytical statistical evaluation of turbulent correlations in the mean-field compressible magnetohydrodynamic (MHD) turbulence are presented with the analytical and model expressions for the transport coefficients. In addition to the usual solenoidal dynamo expressions, such as the turbulent magnetic diffusivity, the alpha effects, etc., the turbulent electromotive force contains several terms arising from strong compressibility, which are represented by the turbulent dilatation or the density variance. Large-scale instability analysis of the perturbed mean fields is performed. It is shown that, depending on the configuration of the mean magnetic field and the mean density, the magnetoclinicity effect may contribute to the growth of the magnetic perturbation at the largest scale. Applications on the astrophysical flow phenomena are discussed.

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  • Shoji KOYAMA
    Type: Research Flash
    2020 Volume 72 Issue 1 Pages 31-35
    Published: January 01, 2020
    Released: January 31, 2020
    JOURNAL FREE ACCESS

    A numerical simulation of grid turbulence with temperature stratification has been conducted using turbulent models. In common grid turbulence, temperature stratification is almost always stable one. In this study, however, the flow with an unstable linear temperature profile passed through a biplanar grid is assumed from the experiment by Thoroddsen et al. (1998) and the turbulence statistics behind the grid are studied. The turbulent model employed is an original model that solves the transport equation for the thermal diffusivity. Results are showed that the model can reproduce the experimental data.

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  • Kazuhiro INAGAKI
    Type: Research Flash
    2020 Volume 72 Issue 1 Pages 37-40
    Published: January 01, 2020
    Released: January 31, 2020
    JOURNAL FREE ACCESS

    In rotating turbulent flows accompanied with spatially inhomogeneous distribution of helicity, it is known that statistically averaged flow spontaneously emerges. In this study, we investigate the phenomenon in terms of not only spatial transport of velocity but also inter-scale transport of kinematic energy in the wavenumber space. We perform a numerical simulation of rotating turbulence in a periodic box in which energy or helicity are driven in spatially confined region. As a result, the energy spectrum which is decomposed only in spatially homogeneous directions does not grow, while the mean velocity profile grows as the time goes by. On the energy spectrum which is defined by decomposing the total energy in the whole system, we can observe the growth of it in the lower wavenumber region than energy injection scale.

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Research Review
  • Mengtao HAN, Ryozo OOKA, Hideki KIKUMOTO
    Type: Research Review
    2020 Volume 72 Issue 1 Pages 41-47
    Published: January 01, 2020
    Released: January 31, 2020
    JOURNAL FREE ACCESS

    Bounceback, a popular wall boundary condition in the lattice Boltzmann method (LBM), is not capable of capturing the accurate shear drag on the wall when addressing high Reynolds number turbulent flows using coarse-grids systems. In this study, we propose a“ wall-function bounce (WFB)” boundary that incorporates a wall function (Spalding’s law) into LBM’s boundary condition and overcomes this shortcoming of bounceback. The WFB boundary calculates the appropriate shear drag on the wall through a wall function model and then modifies distribution functions to reflect the shear drag. Simulations of turbulent channel flow using the LBMbased large-eddy simulation is implemented to validate the proposed boundary. The results indicate that WFB could obtain the proper shear drag on the wall and thus compensated the underestimation of the time-averaged velocity in the buffer layer, especially at the first layer grid, and corrected the mainstream component of the fluctuating velocity near the wall.

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  • Hongyuan JIA, Hideki KIKUMOTO
    Type: Research Review
    2020 Volume 72 Issue 1 Pages 49-55
    Published: January 01, 2020
    Released: January 31, 2020
    JOURNAL FREE ACCESS

    This research proposed a new method for the line source identification by combining the Bayesian inference with the Super-Gaussian function. A simple boundary layer was simulated with CFD (Computational Fluid Dynamics) to obtain the measurements and adjoint concentration flow field. The difference between the measurements and the adjoint concentrations was formulated according to Bayesian theorem to estimate the source parameters stochastically. The Super-Gaussian function was employed to approximate the line source with several tractable coefficients. The results showed that this method is capable of identifying all the parameters without any prior geometric information about the line source as long as enough information is provided by sensors.

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  • Qi ZHOU, Ryozo OOKA
    Type: Research Review
    2020 Volume 72 Issue 1 Pages 57-64
    Published: January 01, 2020
    Released: January 31, 2020
    JOURNAL FREE ACCESS

    Deep Neural Network (DNN) is utilized to predict indoor velocity distribution and temperature distribution.

    The non-dimensional Archimedes number (Ar) is put into the DNN as input parameter. DNN can well reproduce the indoor airflow distribution with the maximum relative error of 8%. The performance of DNN for respective prediction of velocity / temperature distribution is better than that for simultaneous prediction. It requires at least 1000 seconds for each case by CFD simulation while it takes 0.1 second for DNN prediction for each case. The high speed and high precision prediction of DNN for two dimensional non-isothermal indoor air distribution is confirmed.

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  • Bingchao ZHANG, Ryozo OOKA, Hideki KIKUMOTO
    Type: Research Review
    2020 Volume 72 Issue 1 Pages 65-70
    Published: January 01, 2020
    Released: January 31, 2020
    JOURNAL FREE ACCESS

    This paper presents a study on the turbulent structure of the wind velocity field around a rectangular prism building model calculated by large-eddy simulation (LES). Spectral proper orthogonal decomposition (SPOD), which is a combination of proper orthogonal decomposition (POD) and discrete Fourier transformation (DFT), was applied in order to extract the physical phenomenon with the largest kinetic energy from the velocity field on a plane near the floor. The obtained eigenfunctions showed the spatio-temporal structures of all kinds of vortex shedding including the Kármán's-type vortex. Also, the obtained eigenvalues showed the kinetic energy distribution for all the vortexes, which gave a possible means to improve the pedestrian wind comfort.

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Research Flash
  • Jinxin ZHOU, Takero YOSHIDA, Junbo ZHANG, Shuchuang DONG, Qiao LI, Dai ...
    Type: Research Flash
    2020 Volume 72 Issue 1 Pages 71-75
    Published: January 01, 2020
    Released: January 31, 2020
    JOURNAL FREE ACCESS

    Ecopath model coupled with MEC (Marine Environment Committee) ocean model was initially developed, and we applied this model to the environment of Onagawa Bay in order to investigate the environmental effect of aquaculture system, which includes the farming of silver salmon and oyster. As a result, the MEC-Ecopath ocean model was approximately validated through comparing observed and simulated results. Focusing on dissolved oxygen, nitrogen and phosphorus concentrations, it was found that salmon aquaculture puts heavier influence on environment than oyster aquaculture. Finally, regarding a discrepancy laid between observed and simulated results, modelling and the calibration of parameters should be improved as future studies.

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  • Shuchuang DONG, Jinxin ZHOU, Qiao LI, Takero YOSHIDA, Daisuke KITAZAWA
    Type: Research Flash
    2020 Volume 72 Issue 1 Pages 77-80
    Published: January 01, 2020
    Released: January 31, 2020
    JOURNAL FREE ACCESS

    In order to evaluate the environmental capacity quantitatively, we investigated the environmental impacts of silver salmon farming in Miho bay by numerical simulation. Terrestrial load through the rivers, and aquaculture waste load were considered as the external conditions. A nested grid system was introduced in numerical simulations. As a result, seasonal variations of total nitrogen, total phosphorus, chemical oxygen demand, and dissolved oxygen concentration were reproduced. Water quality varied around the farm. However, the change in dissolved oxygen concentration indicated that fish farming had little direct impact on the surrounding environment under this simulation condition. In the future, aquaculture waste load models should be improved, and a benthic model should be introduced.

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Research Review
  • Noriaki KOBAYASHI, Yasumasa SUZUKI, Chisachi KATO
    Type: Research Review
    2020 Volume 72 Issue 1 Pages 81-86
    Published: January 01, 2020
    Released: January 31, 2020
    JOURNAL FREE ACCESS

    To clarify the mechanism for aerodynamic sound to be generated from an airfoil in a flow with turbulence, numerical simulations have been carried out for a flow around an airfoil subjected to the wake of a circular cylinder. The test airfoil has the NACA0012 profile with a chord length of 150 mm and a spanwise length of 7.5 mm, and it is set at angle of attack of 9 degrees. The wind velocity is set to 30 m/s, which results in an airfoil Reynolds number of 3.0 × 105. The circular cylinder is set 100 mm upstream of the leading edge of the airfoil. When they flow near the leading edge of the airfoil, the vortices in the cylinder wake are stretched due to the acceleration of the main flow, forms strong source of sound, and radiated intense sound in the upstream direction.

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Research Flash
  • Yoshinobu YAMADE, Chisachi KATO, Hiroyoshi WATANABE
    Type: Research Review
    2020 Volume 72 Issue 1 Pages 87-91
    Published: January 01, 2020
    Released: January 31, 2020
    JOURNAL FREE ACCESS

    Overset method implemented to finite-element-method (FEM) based flow solver for large eddy simulation (LES) was improved for higher rate of convergence and lower numerical errors. In the improved method, pressure is implicitly interpolated in a matrix solver for solving continuity equation with an additional term to guaranty continuity of velocity field at overset boundary. The method was tested in LES of internal flow of a centrifugal pump which composed of 12 impeller blades with a diameter of 318 mm. The accuracy of LES were evaluated by comparing predicted results of pump performance, torque power and discharge flow rate with those measured.

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