Laser sheet imaging of recirculation zone of backward-facing step flow with gas injection

Harinaldi, Toshihisa Ueda, M. Mizomoto

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

Flow mixing in the recirculation zone of a backward-facing step flow (free stream velocity, U = 10 m/s, and step height, H = 20 mm) with gas injection is visualized by laser sheet imaging, based on the Miescattering concept. Two types of imaging have been done. Instantaneous visualization was done by using an Nd-Yag pulse laser. The continuous visualization, on the other hand, was done by using argon ion laser and a high-speed video camera to discuss the continuous motion of mixing. The study focuses on the effects of the specific momentum ratio (I = 0.04, 0.1 and 0.3) and the location of injection of nitrogen gas from a two-dimensional slot port (I1/H = 2 and 4) on the dynamic nature of the injected gas trajectory and gas distribution in the recirculation zone. The result shows that with higher specific momentum ratio, in case of the injection at near step (I1/H = 2), the injected gas distributes more toward upstream since the fluid dynamics restriction is less due to a lower recirculating flow velocity. Meanwhile, in case of injection near the reattachment point (I1/H = 4), the injected jet, which penetrates the flow field deeply, is deflected by the free stream so that the gas distributes more toward the downstream region. In both cases, the mean normalized luminosity in the region where the gas distributes more is no less than 1.6 times that in the region where it distributes less. Mixing is more rapid and intense in case of injection near the reattachment point due to higher turbulence. Furthermore, two frequency modes in the motion of the injected gas jet can be observed. The lower frequency mode associated with the shortening-lengthening of the recirculation zone (flapping) is not affected, whilst the higher one associated with the interaction of vortical motion of the flow field and the injected jet flow is influenced by the specific momentum ratio of injection.

Original languageEnglish
Pages (from-to)351-359
Number of pages9
JournalJournal of Chemical Engineering of Japan
Volume34
Issue number3
DOIs
Publication statusPublished - 2001 Mar

Fingerprint

Gases
Imaging techniques
Lasers
Momentum
Flow fields
Visualization
Argon
High speed cameras
Video cameras
Fluid dynamics
Flow velocity
Luminance
Laser pulses
Turbulence
Nitrogen
Trajectories
Ions

Keywords

  • Backward-facing step
  • Gas injection
  • Gas mixing
  • Laser sheet imaging
  • Recirculation flow

ASJC Scopus subject areas

  • Chemical Engineering(all)

Cite this

Laser sheet imaging of recirculation zone of backward-facing step flow with gas injection. / Harinaldi; Ueda, Toshihisa; Mizomoto, M.

In: Journal of Chemical Engineering of Japan, Vol. 34, No. 3, 03.2001, p. 351-359.

Research output: Contribution to journalArticle

Harinaldi ; Ueda, Toshihisa ; Mizomoto, M. / Laser sheet imaging of recirculation zone of backward-facing step flow with gas injection. In: Journal of Chemical Engineering of Japan. 2001 ; Vol. 34, No. 3. pp. 351-359.
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abstract = "Flow mixing in the recirculation zone of a backward-facing step flow (free stream velocity, U = 10 m/s, and step height, H = 20 mm) with gas injection is visualized by laser sheet imaging, based on the Miescattering concept. Two types of imaging have been done. Instantaneous visualization was done by using an Nd-Yag pulse laser. The continuous visualization, on the other hand, was done by using argon ion laser and a high-speed video camera to discuss the continuous motion of mixing. The study focuses on the effects of the specific momentum ratio (I = 0.04, 0.1 and 0.3) and the location of injection of nitrogen gas from a two-dimensional slot port (I1/H = 2 and 4) on the dynamic nature of the injected gas trajectory and gas distribution in the recirculation zone. The result shows that with higher specific momentum ratio, in case of the injection at near step (I1/H = 2), the injected gas distributes more toward upstream since the fluid dynamics restriction is less due to a lower recirculating flow velocity. Meanwhile, in case of injection near the reattachment point (I1/H = 4), the injected jet, which penetrates the flow field deeply, is deflected by the free stream so that the gas distributes more toward the downstream region. In both cases, the mean normalized luminosity in the region where the gas distributes more is no less than 1.6 times that in the region where it distributes less. Mixing is more rapid and intense in case of injection near the reattachment point due to higher turbulence. Furthermore, two frequency modes in the motion of the injected gas jet can be observed. The lower frequency mode associated with the shortening-lengthening of the recirculation zone (flapping) is not affected, whilst the higher one associated with the interaction of vortical motion of the flow field and the injected jet flow is influenced by the specific momentum ratio of injection.",
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