Journal of Fluid Science and Technology
Online ISSN : 1880-5558
ISSN-L : 1880-5558
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  • Takayuki MATSUNUMA, Takehiko SEGAWA
    2019 Volume 14 Issue 2 Pages JFST0007
    Published: 2019
    Released: July 30, 2019
    JOURNALS FREE ACCESS

    Dielectric barrier discharge (DBD) plasma actuators were used for the active control of flow separation on a curved wall simulated suction surface of a gas turbine blade at three different mainstream velocities, UMS = 2.2 m/s, 4.1 m/s, and 6.3 m/s. Owing to the change in mainstream velocity, the Reynolds number was varied as Re = 1.7 × 104, 3.1 × 104, and 4.7 × 104, respectively. Particle image velocimetry system was used to obtain two-dimensional velocity field measurements. The amplitude of input voltage for the plasma actuator was changed from ±2.0 kV to ±4.0 kV. At the lower mainstream velocity, UMS = 2.2 m/s (Re = 1.7 × 104), the separated flow induced on a curved wall was consider-ably reduced by the flow control using the DBD plasma actuator. Moreover, the effect of flow control by the plasma actuator was gradually reduced at the higher mainstream velocities, UMS = 4.1 m/s and 6.3 m/s (Re = 3.1 × 104 and 4.7 × 104, respectively). The flow control effect was improved by changing the position of the plasma actuator. When the plasma actuator was positioned immediately before the separation point, it exhibited better flow control effects than when positioned immediately behind the separation point.

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  • Kensuke OKADA, Masato HIROTA, Seiichiro IZAWA, Yu FUKUNISHI
    2019 Volume 14 Issue 2 Pages JFST0008
    Published: 2019
    Released: August 27, 2019
    JOURNALS FREE ACCESS

    A wind tunnel experiment was performed to investigate the suitable conditions in which a localized turbulent region can easily be generated in a flat-plate boundary layer. An artificial disturbance of zero-mass flux was introduced upstream using a combination of a short-duration jet and suctions to prepare a potentially unstable environment. The disturbed region by itself decayed downstream. Another jet was then ejected downstream at several different timings and two different spanwise locations relative to the passage of the locally disturbed region to promote transition to turbulence. Although the jet was too weak to trigger the turbulence transition by itself, an isolated turbulent region, the so-called turbulent spot, was generated when ejected against the disturbed region. The optimum conditions were found when the jet was ejected between the high- and low-speed areas of the convecting unstable region.

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  • Toshihiko SHAKOUCHI, Tsubasa TANOUE, Koichi TSUJIMOTO, Toshitake ANDO
    2019 Volume 14 Issue 2 Pages JFST0009
    Published: 2019
    Released: September 19, 2019
    JOURNALS FREE ACCESS

    The flow characteristics of sub- and supersonic under-expanded jets issued from circular nozzles have been studied well; however, this does not apply to sub- and supersonic jets from an orifice nozzle. In this study, the flow characteristics of sub- and supersonic jets issued from an orifice or notched special orifice nozzle are examined experimentally based on the results of a visualized flow pattern by the Schlieren method and the measurements of velocity distribution by a thin supersonic Pitot tube. That is, the effects of the nozzle shape on the flow characteristics such as the decay of the jet centerline velocity, velocity distribution at the cross section, increment of the jet- width and -flow rate to the downstream are examined experimentally. Results indicate that the jet issued from the notched orifice nozzle with a rectangular notch demonstrates excellent entrainment performance. In addition, to improve the performance of a cylindrical ejector, the application of the results is examined.

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