SEISAN KENKYU
Online ISSN : 1881-2058
Print ISSN : 0037-105X
ISSN-L : 0037-105X
Volume 67 , Issue 1
Showing 1-14 articles out of 14 articles from the selected issue
Special Issue on Turbulence Simulation and Flow Design
Introduction to Special Section
Research Flash
  • Fujihiro HAMBA
    2015 Volume 67 Issue 1 Pages 3-6
    Published: January 01, 2015
    Released: February 24, 2015
    JOURNAL FREE ACCESS
    On the basis of the two-point velocity correlation the energy density in the scale space was introduced to better understand inhomogeneous turbulence. The transport equation for the energy density was derived for inhomogeneous turbulence. As a first step of analysis, using the direct numerical simulation of homogeneous isotropic turbulence, the transport equation for the energy density was evaluated and compared to the energy spectrum equation in the wavenumber space. As a result, it was shown that the energy density newly defined can be used to appropriately examine the energy transfer in the scale space.
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Research Review
  • Taketo ARIKI, Fujihiro HAMBA
    2015 Volume 67 Issue 1 Pages 7-10
    Published: January 01, 2015
    Released: February 24, 2015
    JOURNAL FREE ACCESS
    In this article a statistical- theoretical methodology for inhomogeneous turbulent flow is briefly explained. The theory is prominent in its theoretical basis; it is formulated on the coordinate system convected by the mean flow, which is referred to as the mean-Lagrangian coordinate system. By applying the renormalized perturbation theory to the fluid equation on the mean-Lagrangian coordinate system, the history effect is represented in the similar manner to that of the homogeneous case. As an example, we apply the present methodology to the Reynolds stress and derive the history effect. Applying the temporal-locality approximation, we also derive a non-linear eddy-viscosity representation, which may be a generalization of a familiar type of models.
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Research Flash
  • Shoji KOYAMA
    2015 Volume 67 Issue 1 Pages 11-15
    Published: January 01, 2015
    Released: February 24, 2015
    JOURNAL FREE ACCESS
    Natural convection between two differently heated vertical walls is investigated by the simulation with turbulence models. Since to our knowledge there are few simulation examples of such convection, we attempt to confirm whether we can obtain appropriate results when using several known models. These models are the standard k−ε model, the two-equation model for thermal field by Yin et al. (1989), and the three-equation model by Yoshizawa et al. (2012), which its three representative variables are turbulent viscosity, kinetic energy, and dissipation rate. It is revealed that those models are able to reproduce the mean velocity and temperature to some extent. In particular, the result obtained by the Yoshizawa model with a vertical heat-flux model is in good agreement with DNS data.
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  • Nobumitsu YOKOI
    2015 Volume 67 Issue 1 Pages 17-23
    Published: January 01, 2015
    Released: February 24, 2015
    JOURNAL FREE ACCESS
    A new simple model for the solar activity cycle is proposed. The present model differs from the previous ones mainly in two points. First, in addition to the helicity coefficient $¥alpha$, we consider a term related to the cross helicity, which represents the effect of the inhomogeneous mean flow, in the turbulent electromotive force. Second, this transport coefficient( $¥gamma$ ) is not treated as an adjustable parameter, but the evolution equation for $¥gamma$ is simultaneously solved. The basic scenario for the solar activity cycle in this approach is as follows: The toroidal field is induced by the toroidal rotation in mediation by the turbulent cross helicity. Then due to the $¥alpha$ or helicity effect, the poloidal field is generated from the toroidal field. The poloidal field induced by the $¥alpha$ effect produces a turbulent cross helicity whose sign is opposite to the original one (negative cross-helicity production). The cross helicity with this opposite sign induces a reversed toroidal field. Results of the eigenvalue analysis of the model equations are shown, which confirm the above scenario.
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Research Review
  • Yusuke ARIMA, Ryozo OOKA, Hideki KIKUMOTO, Toru YAMANAKA
    2015 Volume 67 Issue 1 Pages 25-30
    Published: January 01, 2015
    Released: February 24, 2015
    JOURNAL FREE ACCESS
    Climate change such as global warming is proceeding and climate conditions have huge impact on the building performance. Building energy simulation is conducted to adapt a building to climate conditions using weather data which consists of weather components such as temperature and solar radiation. At present, it is common to use weather data which are based on current or past weather conditions. However, most buildings have a lifespan of several decades, during which climate can gradually change. Therefore, energy simulations should incorporate climate change predictions in order to ensure that buildings are adaptable to future climatic conditions and have long-term high building performance. The purpose of this study is to construct future weather data for the building energy simulations which based on the future climate conditions using a dynamical downscaling method with a global climate model.
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  • Keigo NAKAJIMA, Ryozo OOKA, Hideki KIKUMOTO
    2015 Volume 67 Issue 1 Pages 31-37
    Published: January 01, 2015
    Released: February 24, 2015
    JOURNAL FREE ACCESS
    Large-eddy simulation (LES) is performed to make the database to investigate the momentum transfer mechanism and to evaluate the prediction accuracy of RANS within and above the urban canyon. The prediction accuracy of RANS within and above the urban canyon is investigated by comparing with the LES database. RANS fails to reproduce the spatial distribution of mean wind velocity and underestimates turbulent kinetic energy and Reynolds stress <u1'u3'> within the urban canyon. The budget of Reynolds stress <u1'u3'> transport equation is analyzed using LES database to investigate the momentum transfer mechanism and to evaluate the validity of Reynolds stress <u1'u3'> modeling. Diffusion term of Reynolds stress <u1'u3'> transport equation increases within the urban canyon. The gradient diffusion approximation of Reynolds stress <u1'u3'> is not valid within the urban canyon because nonlocal effect like diffusion term increases within the urban canyon. It is necessary to apply the turbulence model of Reynolds stress <u1'u3'> that is able to express nonlocal effect like diffusion term within the urban canyon.
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Research Flash
  • Junbo ZHANG, Daisuke KITAZAWA
    2015 Volume 67 Issue 1 Pages 39-43
    Published: January 01, 2015
    Released: February 24, 2015
    JOURNAL FREE ACCESS
    As one of aquaculture facilities, the design of fish cages is significantly important for fish farm. To understand the effect of water flow reduction due to drag of fish cage on stratification structures, Marine Environmental Committee (MEC) ocean model coupling with the drag of fish cage submodel was run. As a result, fish cage influences water flow both in velocity and direction, and the attenuation of water flow mainly depends on incident direction. Scenario simulations indicate that bio-fouling of fish cage netting further reduces flow velocity and enlarges stratifications, resulting in potential unfavorable conditions for vertical transport of dissolved oxygen.
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  • Daisuke KAWAHARA, Shinsuke KATO
    2015 Volume 67 Issue 1 Pages 45-48
    Published: January 01, 2015
    Released: February 24, 2015
    JOURNAL FREE ACCESS
    There is an urgent demand worldwide for the implementation of low-energy buildings. Standard glass windows are associated with heat loss issues, and a high risk of moisture condensation due to relatively poor insulating qualities, and these window types are often prone to substantial heat loss via heat conduction. To deal with these problems, this paper proposes an air supply Dynamic Insulation (DI) window system applied to installed windows, combined with a mechanical ventilator. Comparing the DI window and the general vent cap, the general vent cap exhibited a wider temperature distribution than the DI window.
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Research Review
Research Flash
  • Soma KITA, Kazuo SHIMAZAKI, Yasuharu YAJIMA, Susumu OMURA, Takashi ONO ...
    2015 Volume 67 Issue 1 Pages 55-58
    Published: January 01, 2015
    Released: February 24, 2015
    JOURNAL FREE ACCESS
    The influence that maxillary movement gives for breathing is great, and it needs a functional evaluation. But there is not the report about stenosis of the nasal cavity with the maxillary bone upward movement. Therefore we analyzed it for the purpose of clarifying the influence that maxillo-mandibular orthognathic surgery with the maxillary bone upward movement gave for a nose breathing function.
    By moving maxillary bone above and resecting inferior border of the pyriform aperture, the pressure drop of the nasal cavity got a result to decrease after surgery. Furthermore, it was recognized that a lot of pressure drop occurred in nasal cavity front 1/3, and the possibility that resecting inferior border of the pyriform aperture was useful from the viewpoint of nasal cavity ventilation was suggested.
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  • Yoshinobu YAMADE, Chisachi KATO, Akiyoshi IIDA, Shinobu YOSHIMURA, Kei ...
    2015 Volume 67 Issue 1 Pages 59-63
    Published: January 01, 2015
    Released: February 24, 2015
    JOURNAL FREE ACCESS
    Objective of this research is to predict accurately aeroacoustics interior noise of a vehicle for wide range of frequency between 100 Hz and 4 kHz. One-way coupled simulations of CFD, structure analysis and acoustical analysis were performed to predict the interior aeroacoustics noise. We predicted pressure fluctuations on outer surfaces of a vehicle by computing unsteady flow around a vehicle as the first step. Secondary, the predicted pressure fluctuations were fed to structure analysis to predict vibration accelerations on surfaces within a vehicle. Finally, acoustical analysis were performed to predict sound field within a vehicle with the boundary conditions computed by using predicted vibration accelerations by the structure analysis. In this paper, we focus on the unsteady flow computations, which is the first step of the coupled simulations. Large Eddy Simulation were performed to predict the pressure fluctuations on the surface of the test vehicle. Predicted and measured pressure fluctuations at the sampling points on the surface of the test vehicle were compared and confirmed to be agreed well.
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  • Olivier PACOT, Chisachi KATO, Yang GUO, Yoshinobu YAMADE
    2015 Volume 67 Issue 1 Pages 65-70
    Published: January 01, 2015
    Released: February 24, 2015
    JOURNAL FREE ACCESS
    The new trend on the turbine development is to extend the range of operation, both at part load and at full load conditions. However, it is well known that the dynamic of the flow can considerably change leading tounstable conditions. In the worst case, the flow variation can damage significantly the whole power plant.The operation of a turbine at part load or at full load conditions changes the axial and tangential velocity distributions at the inlet of the draft tube inducing the development of the well-known vortex rope. The volume of the vortex rope is changing over time resulting in a pressure variation that can be felt throughout the power plant. It is thus primordial to predict accurately the dynamical behavior of the vortex rope in order to avoid that the Eigen frequency of the vortex rope reach the Eigen frequency of the hydraulic system. Therefore, the challenge is to predict accurately the behavior of the flow field, which requires to take into account the cavitation phenomenon. The present paper focuses first, on a non-cavitating flow to evaluate the accuracy of a LES computation of the vortex rope phenomenon. The computed flow selected is the one in a test model Francis turbine operated at part load condition (65% BEP). Second, a cavitating computation is performed to evaluate the performance of the Okita cavitation model implemented in an in-house LES code. The computed flow selected is the flow around a Clark-Y11.7% for two different Angle Of Attack: 2 and 8 degrees.
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  • Yang GUO, Yoshinobu YAMADE, Chisachi KATO, Yutaka OHTA, Taku IWASE, Ry ...
    2015 Volume 67 Issue 1 Pages 71-75
    Published: January 01, 2015
    Released: February 24, 2015
    JOURNAL FREE ACCESS
    Large eddy simulation (LES) of the internal flow in a centrifugal blower was performed in order to analyze the rotating stall at a partial flow rate. The blower has 12 impeller blades and a vaneless diffuser. Numerical results were validated by comparisons with measurements in terms of static head, velocity distribution at the impeller outlet and propagating speed of a stall cell. Propagating speed of the stall cell is about 70% of impeller rotational speed in both the experiment and the numerical computation. In addition, the sound pressure level (SPL) at a sampling point that is 1 m away from the suction bell-mouth was computed by solving Lighthill’s equation, in which the source term was obtained from the incompressible LES. The computed SPL was compared with the experimental data.
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