Journal of Fluid Science and Technology
Online ISSN : 1880-5558
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Volume 3 , Issue 7
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Papers
  • Islam M. ROFIQUL, Hiroyuki HANIU, Sangil KIM
    Volume 3 (2008) Issue 7 Pages 826-837
    Released: October 07, 2008
    JOURNALS FREE ACCESS
    To innovate an easy and economic way for removal of solid char product from a fixed-bed fire-tube heating pyrolysis reactor the fluid dynamics studies on its cold model are essential. Thus, two types of fluid dynamics experiments have been carried out on a cold model of the pyrolysis reactor: (i) to determine the ejection pressure of the solid char from the reactor, which was carried out with the help of an air compressor and artificial solid char and (ii) to investigate the flow pattern inside the reactor chamber during ejection of char that was conducted by laser Doppler velocimetry (LDV) measurement and flow visualization test. The experimental results show that variation of char ejection pressure with respect to superficial air velocity always follows a polynomial of second-degree. The normalized pressure should be reached to a value about 1.7 with a corresponding normalized superficial air velocity nearly to 1.0, to be started the char product blown out from the reactor model properly. The LDV measurements and visualization test ensure that the spiral char exit port is not able to create a rotary motion inside the reactor chamber during the removal of solid char.
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  • Akira FUJII, Shinichi MIZUNO, Hironori HORIGUCHI, Yoshinobu TSUJIMOTO
    Volume 3 (2008) Issue 7 Pages 838-845
    Released: October 07, 2008
    JOURNALS FREE ACCESS
    In the present paper, a new method for the suppression of unsteady cavitation in a turbopump inducer is proposed. An accumulator with a large volume is placed at the upstream of the inducer to equalize the pressure around the periphery. Through the experiments with the accumulator, it was found that the occurrence region of rotating cavitation at design flow rate decreases and higher order cavitation instabilities are suppressed. However, at low flow rate, higher order cavitation instabilities were found when the clearance opened to the accumulator was too large.
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  • Yuya BABA, Ryoichi KUROSE
    Volume 3 (2008) Issue 7 Pages 846-856
    Released: November 05, 2008
    JOURNALS FREE ACCESS
    The detailed behaviors of gaseous and spray lifted flames are studied by two- dimensional direct numerical simulations (DNS), and the characteristics of the flamelets are investigated in terms of two key variables for flamelet modeling, namely mixture fraction and scalar G. The results show that both the gaseous and spray lifted flames are partially premixed flames, in which premixed and diffusion flames co-exist and the premixed flame stabilizing the flames precedes to the diffusion flame. The non-combusting and combusting regions can be generally discriminated by the scalar G, and the premixed and diffusion flames in the combusting region can be predicted by flame index, respectively. Although the flamelets in the diffusion flame of the gaseous lifted flame are characterized by the mixture fraction and scalar dissipation rate, those on the spray lifted flame are not. To account for the flamelet characteristics of the spray lifted flame, flamelet/progress-variable approach needs to be introduced.
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  • Jin-Sheng LEU, Chien-Nan LIN
    Volume 3 (2008) Issue 7 Pages 857-867
    Released: November 11, 2008
    JOURNALS FREE ACCESS
    The purpose of this work is to evaluate the magnetic effect on the MHD free convection along an inclined plate with variable surface temperature. The viscous dissipation and Joule heating effects are taken into account. The numerical solution is obtained by utilizing a fully implicit finite difference method and examined for the coupled effects of magnetic parameter M, inclination angle φ, exponent values of power-law relation n, and Prandtl number Pr on the local and average flow and heat transfer characteristics. The results show that the presence as well as the increase in the magnetic field decreases velocity and heat transfer performance. The influences of M are more significant for smaller n and Pr. For Pr=0.01 and n=-1/3, the average Nusselt number Nuav(M=4) is decreased 83.3% relative to that of Nuav(M=0). In addition, the velocity, temperature gradient, and Nusselt numbers are increased with the increase of φ, Pr and n.
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  • Masaya SUZUKI, Kazuaki INABA, Makoto YAMAMOTO
    Volume 3 (2008) Issue 7 Pages 868-880
    Released: November 13, 2008
    JOURNALS FREE ACCESS
    Sand erosion is a phenomenon whereby solid particles impinging on a wall cause serious mechanical damage to the wall surface. The performance and lifetime of various machines, such as airplanes, ships, gas turbines, and pumps, are severely degraded by sand erosion. This phenomenon is a typical gas-particle two-phase turbulent flow and can be considered as a multi-physics problem in which the flow field, particle trajectory, and wall deformation interact. However, neither the change of the flow field nor the related particle trajectory during the erosion process has been taken into account in conventional simulations. This treatment is physically unrealistic. Hence, we have developed a numerical procedure by which to investigate the sand erosion phenomenon, including the temporal change of the flow field and the wall shape. In the present study, we simulate sand erosion of a 90-degree bend with a square cross-section. Bend erosion is the typical subject of sand erosion experiments and is useful for the verification of numerical simulations. The numerical results are compared with experimental data and it is confirmed that the developed code can capture the sand erosion phenomenon reasonably.
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  • Hiroshi FUKUOKA, Minoru YAGA, Toshio TAKIYA
    Volume 3 (2008) Issue 7 Pages 881-891
    Released: November 13, 2008
    JOURNALS FREE ACCESS
    The unsteady behavior of a flow driven by a jet suddenly injected into cells is investigated numerically by solving the axisymmetric two-dimensional compressible Navier-Stokes equations. The system of the calculation is a model of laser ablation of a certain duration followed by a discharging process through the exit hole at the downstream end of the cell. The parameters for the calculations are the diameter of the cell, the exit diameter of the cell and the duration of the injected jet. The velocity monitored at the exit hole is used to evaluate the influence of the shape and the exit diameter of the cell on the shock wave, the plume, and their interactions. As a result, it was found that the position in which the shock wave converges and the focal point of the elliptical cell are almost the same for various parameters. The spreading shock wave that converged at the geometrical focal point reflects from the cell wall and this shock wave alternate between the jet injection and the cell exit. It was also found that the number of peaks and the maximum velocity downstream of the cell exit are roughly determined by the contour of the walls of the elliptical cell.
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  • Yoshihiro KATO, Igor MEN'SHOV, Yoshiaki NAKAMURA
    Volume 3 (2008) Issue 7 Pages 892-905
    Released: November 27, 2008
    JOURNALS FREE ACCESS
    A method for performing aeroacoustic simulation, in which the acoustic field is split from the flow field, is applied to the flow around automobile rear-view mirrors placed on a large solid plane. The flow can be obtained by performing large eddy simulation for the incompressible flow equations on colocated grids, while the acoustic equations are defined by the difference between the compressible and the incompressible flow equations, and solved by the finite volume method with the fourth order WENO scheme. The non-reflecting boundary conditions with a perfectly matched layer are applied to the outer boundary. Calculated results show clear sound emissions, where acoustic streamlines depict the propagation path based on acoustic intensity vectors. In this paper, two kinds of mirror shape, i.e., the cases with and without a strong vortex at the tip of the rear-view mirror, are compared. Calculated results show some differences between them in the acoustic field. The sound pressure related to the pressure frequency of the generated vortex is increased in all directions, though the propagation path does not show a large difference except near part of the body surface.
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  • Mohammad GHAFFARPOUR, Alireza NOORPOOR
    Volume 3 (2008) Issue 7 Pages 906-920
    Released: November 28, 2008
    JOURNALS FREE ACCESS
    This paper presents experimental data on the characteristics of a kerosene spray flame produced by a hollow-cone pressure-atomized nozzle in a swirl-stabilized combustor. These acquired data include the volume flux distribution, size and velocity distribution, measured by use of Phase Doppler Particle Analyzer (PDPA). The effects of swirl number on different parameters, recirculation zone, and stability of the flame is investigated. The data is offered for use in assessments of two-phase flow computational methods as are useful to gas turbine and furnace combustors design procedure. The overall characteristics of this spray flame were defined.
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