Journal of Fluid Science and Technology
Online ISSN : 1880-5558
最新号
選択された号の論文の10件中1~10を表示しています
Special Issue of the Fourteenth International Conference on Flow Dynamics (ICFD2017)
Papers
  • Hiroko KITAOKA
    2018 年 13 巻 4 号 p. JFST0023
    発行日: 2018年
    公開日: 2018/11/09
    ジャーナル フリー

    Since gas exchange in the human lung is mass transports by fluids, respiratory physiology should be based on fluid dynamics. However, current theories of respiratory physiology have been established by regarding the respiratory system as an analogy of electric circuit where the airflow is assumed laminar, and led clinicians to wrong ways. In this paper, two representative cases are introduced. One is a popular pulmonary function test and the other is an artificial ventilation method for severe respiratory failure. Maximum forced expiration test is used for diagnosis of expiratory airflow limitation such as emphysema or chronic obstructive pulmonary disease (COPD). Although the cause of expiratory airflow limitation has been believed to be due to small airway obstruction, its true cause is the collapse of the intra-thoracic large airway. The mechanism of high-frequency ventilation (HFV), one of artificial ventilations with tiny tidal volume, has been believed that high frequency oscillation augments gas dispersion and improves gas exchange in spite of tiny tidal volume. However, recent clinical studies have revealed that HFV is useless for acute respiratory distress syndrome (ARDS) in adults. The true gas transport mechanism with tiny tidal volume is asymmetric airflow profile between inspiration and expiration due to the presence of bronchial bifurcations. In both cases, there are several papers published in famous journals more than 25 years ago, which stated the true mechanisms but currently have been seldom refereed. Reconstruction of respiratory physiology is an urgent task both for medical and engineering researchers.

  • Takafumi OKUMA, Tomoyuki IMATSUJI, Taro HASHIZUME, Manabu TANAKA, Taka ...
    2018 年 13 巻 4 号 p. JFST0024
    発行日: 2018年
    公開日: 2018/11/09
    ジャーナル フリー

    Temperature characteristics of a multiphase AC arc in various working pressures were investigated by an innovative observation system consisting of a high-speed video camera and band-pass filters. Thermal plasmas have been widely applied to many industrial fields because of their unique advantages such as high temperature, high enthalpy, and rapid quenching capability. In particular, the multiphase AC arc is advantageous in terms of large plasma volume and high energy efficiency. Therefore, this heat source has been applied to innovative material processing such as in-flight glass melting, and functional nanoparticles fabrication. However, the temperature field and its fluctuation characteristics in the multiphase AC arc have not been understood because of the difficulties of temperature measurement due to their rapid fluctuation in millisecond timescale as well as the axisymmetric spatial characteristics. To understand and control the fluctuation phenomena is important to realize this method as industrial technology. Temperature measurement system using a high-speed camera was constructed to visualize the temperature fields of the multiphase AC arc. The fluctuations in the two-dimensional intensity distributions of particular line emissions from atomic argon were successfully observed. By analyzing these images using the Boltzmann plot method, the temperature distribution was estimated. The experimental results indicated that the arc temperature fluctuated in the range from 6,000 to 12,000 K. Higher temperature, smaller arc existence area, and decrease in the diameter of the arc were observed with an increase of working pressure. The arc temperature in the multiphase AC arc is sufficiently high to treat the refractory metals and ceramics powders at high processing rate.

  • Wataru YAMAZAKI, Tatsuya KATO, Tsubasa HOMMA, Koji SHIMOYAMA, Shigeru ...
    2018 年 13 巻 4 号 p. JFST0025
    発行日: 2018年
    公開日: 2018/11/09
    ジャーナル フリー

    In this research, 2D shallow water equations are expanded by an intrusive polynomial chaos approach for efficient uncertainty quantification in tsunami inundation flows. Uncertainty propagation can be evaluated by solving the expanded 2D shallow water equations, and then probability measures such as mean, standard deviation and probability density function can be obtained for arbitrary variables. An uncertain input is given on its initial condition of water height and/or bathymetry in dam break problems as well as in Thacker’s inundation flow problem. Obtained uncertainty quantification results are compared with (exact) Monte-Carlo simulation results to validate the developed approach. Qualitative agreement can be confirmed between the Monte-Carlo simulation and the developed approach. The computational cost of the developed approach is much more inexpensive than the Monte-Carlo simulation, so that inexpensive/accurate uncertainty quantification can be realized with the developed approach. By using the obtained results, stochastic hazard map considering uncertainties can be generated which will be beneficial to minimize potential damage via inundation flows.

  • Yosuke OGINO, Yoshinori HIRATA, Satoru ASAI
    2018 年 13 巻 4 号 p. JFST0026
    発行日: 2018年
    公開日: 2018/11/09
    ジャーナル フリー

    In this study, to make clear the phenomena of the gas metal arc welding process more deeply, a simulation model including both the arc plasma and the metal transfer phenomena is constructed and influence of the arc current is numerically investigated. The simulation model used in this study considered the iron vapor generating from the high-temperature metal surface and surface deformation of the molten metal as the interaction between the arc plasma and the molten metal. The simulation result shows that the molten wire glows largely at the wire tip when the arc current is low. On the other hand, for the high arc current, small droplet detaches from the wire tip. These simulation results of the behavior of the molten metal show good agreement with the experimental results. The balance of the driving force acting on the molten metal at the wire tip is very important to determine the molten metal behavior, and when influence of the electromagnetic force becomes stronger than that of the surface tension, the transfer mode is changed. In addition, simulation and experiment are carried out using the same pulsed current, these results of the arc plasma and the molten metal show good agreement. Therefore, the simulation model constructed in this study can describe the phenomena depending on the arc current. These results show that there are possibilities to be able to predict the behavior in gas metal arc welding process and optimize the current profile by the simulation model for controlling the gas metal arc welding phenomena.

  • Manabu TANAKA, Hirohiko SOEDA, Takayuki WATANABE, Tomohiro KOGA
    2018 年 13 巻 4 号 p. JFST0027
    発行日: 2018年
    公開日: 2018/11/09
    ジャーナル フリー

    Fluctuation characteristics of plasma jet flow in an innovative long DC arc system with ring-shaped anode were successfully clarified on the basis of the high-speed camera visualization. The long DC arc with long electrode gap distance more than 350 mm has been applied to gas decomposition due to its advantages such as large plasma volume and long residence time of treated gas. However, large heat loss at a conventional hemispherical-shaped anode was critical issue in the long DC arc system. Therefore, a ring-shaped anode was utilized to convert large energy loss at the anode into the plasma jet flow. Two kinds of the experiments were conducted. One was the estimation of energy balance in the long DC arc system. Calorimetric measurements were carried out. Another was the high-speed camera observation of the arc fluctuation and the plasma jet fluctuation. Results indicated that the 60% of heat loss at the conventional hemispherical-shaped anode was converted into the plasma jet flow when the ring-shaped anode was utilized. High-speed camera observation revealed that the plasma jet fluctuation with sharp FFT peak in the range of 25-500Hz was attributed to the arc fluctuation, which originated from the restrike phenomena of the anode spot. In contrast, results also suggested that the plasma jet fluctuation with broad FFT peaks in the range of 100-300Hz was attributed to the eddy formation due to the entrainment of ambient cold gas. To understand and control the fluctuation phenomena in the plasma jet enables to establish the innovative waste treatment by thermal plasmas.

  • Hikaru YAMADA, Lin CHEN, Junnosuke OKAJIMA, Atsuki KOMIYA, Shigenao MA ...
    2018 年 13 巻 4 号 p. JFST0028
    発行日: 2018年
    公開日: 2018/11/09
    ジャーナル フリー

    The objective of this study is to visualize the flow pattern in methane hydrate (MH) reservoir model under atmospheric pressure condition. A method to mimic a real MH reservoir was introduced into the present research to visualize the multiphase flow pattern in porous media under thermal fluid injection. First, porous media mimicking real MH reservoir were prepared in a visualization cell with dual horizontal wells, which were composed of glass beads, ice of sodium bicarbonate (NaHCO3) aqueous solution and ethanol (C2H5OH). Thereafter, hydraulic fracturing by injecting C2H5OH aqueous solution was executed to generate flow path that increases permeability between the injection well and production well. The flow pattern in the reservoir model with the flow path was then visualized during the injection of hydrochloric acid (HCl) aqueous solution. The dominant factors governing the multiphase flow in fractured porous MH mimicking reservoir were evaluated. It was found that the flow path formation with high permeability by hydraulic fracturing and permeability increment by ice melting are of critical importance for the reservoir mimicking system. In addition, it is found that the liquid phase flow may also be affected by the formation of gas phase inside the porous media that mimic the dissociation process in the real MH reservoir.

  • Nobuhiro KIMURA, Kei OBATA, Koki KITAGAWA, Toru SHIMADA
    2018 年 13 巻 4 号 p. JFST0029
    発行日: 2018年
    公開日: 2018/11/09
    ジャーナル フリー

    Altering-intensity Swirling-Oxidizer-Flow-Type (A-SOFT) hybrid rocket engine (HRE) was proposed as a technique to solve problems of current hybrid rockets. It uses axial and tangential oxidizer injections and their mass flow rates are manipulated independently to control the thrust and O/F. The visualization experiment of combustion of gaseous oxygen (GOX) and polymethyl methacrylate (PMMA) of A-SOFT HRE is carried out under combustion pressure of 1 bar. Combustion gas flow in the combustor is captured by high speed cameras whose fps is 30000. In order to capture the nature of the flow field quantitatively, obtaining velocity profiles by image analysis applied to its visualization images is effective. Basic image analysis method is Direct Cross Correlation method and, for high precision and spatial resolution, Correlation Based Correction is applied recursively. Averaged velocity profiles are obtained by averaging the calculation results of 10000 images corresponding to the actual time duration of 0.3 s. Flames with strong white light emission are characteristic of hybrid rockets and regarded as traceable markers for the image analysis. These luminous flames are considered to flow in the boundary layer and velocity of flames in the boundary layer is important to capture the characteristics of combustion flow field. Axial velocity of the luminous flame is proportional to the total mixed mass flow rate for each location x. Tangential velocity is proportional to angular momentum given by tangential GOX injection and inversely proportional to the total mixed mass flow rate for each location x. And how much GOX injected in axial and tangential directions are mixed is speculated by velocity profiles. It is found that mixing of GOX injected in axial and tangential directions occurs at almost the same constant rate regardless of the ratio of GOX mass flow rate injected in axial and tangential directions.

  • Atsuki KOMIYA, Kengo SATO, Junnosuke OKAJIMA
    2018 年 13 巻 4 号 p. JFST0030
    発行日: 2018年
    公開日: 2018/11/09
    ジャーナル フリー

    This study focuses on the diffusion phenomena in ethanol-water systems. The diffusion coefficient of ethanol-water systems has a strong concentration dependency originating from intermolecular interactions and the association of molecules in solution. Recently, it has been suggested that flavor variation in whiskey is partly due to different storage conditions that can affect molecular structure variation. To evaluate the molecular structure variation, diffusion coefficient measurements are considered effective. To quantitatively evaluate the variations in the diffusion process and measure the mass diffusion coefficient, the analysis method was improved to measure the concentration field more precisely. Two ethanolic solutions were prepared in this study: one preserved under normal conditions and the other was stored under isothermal conditions for 496 days. By comparing diffusion processes occurring under different storage conditions, the different diffusion coefficients were determined and the effect of storage conditions was discussed. The diffusion coefficient of the ethanolic solution stored under an isothermal condition was smaller than that of the solution stored under normal conditions.

  • Kohei OZAWA, Toru SHIMADA
    2018 年 13 巻 4 号 p. JFST0031
    発行日: 2018年
    公開日: 2018/11/09
    ジャーナル フリー

    The characteristics of several O/F control methods for hybrid rocket propulsion have been discussed and theoretically analyzed from the physical properties of propellants and fuel regression behavior. In this research, comparisons have been made among different oxidizer injection methods of Altering-intensity Swirling Oxidizer Flow Type (A-SOFT), Aft-chamber Oxidizer Injection Method (AOIM), and Swirling-AOIM for the throttle range with a constant O/F, design restrictions of the fuel grain, penalties on the adoption of the methods, and suitable scales of the engine. Theoretical analysis on regression rates has revealed that A-SOFT has upper and lower limits of throttle while maintaining a constant O/F whereas AOIM does not have any lower limit, and Swirling-AOIM covers both the throttle ranges. The designing restriction of the fuel grain derived from the regression rate behavior has indicated that A-SOFT using paraffin and oxygen has a potential to maintain 50-100% throttle range over a burn. The penalties for the adoption of these O/F control methods have also been discussed from the aspects of the increase in the complexity of the system, structural mass, and pressure drop at the injector for the methods using gaseous injection. The pressure drop has quantitatively been evaluated by relating the available swirl strength with the cross-sectional area and gaseous oxidizer mass flux at the injector. This analysis has revealed 5 times difference in the available swirl strength between the gaseous oxygen and the decomposed gas of 90% hydrogen peroxide. The sizing of the 1st stage of the satellite launcher has revealed that A-SOFT and Swirling-AOIM are suitable for small-scale engines with a propellant mass of 100-102 [ton] using paraffin and liquid oxygen whereas AOIM and Swirling-AOIM are suitable for engines with paraffin and 90% hydrogen peroxide.

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