Flow characteristics and vortical structures of a free jet issuing from rectangular nozzle with four tapered triangular tubes

• Published in: Kikai Gakkai ronbunshū = Transactions of the Japan Society of Mechanical Engineers Vol. 88; no. 905; p. 21-00275
• Main Authors: OUCHI, Riku, KIWATA, Takahiro, KONO, Takaaki, KAJITANI, Naoki, TERAMOTO, Hiroshi
• Format: Journal Article
• Language: Japanese
• Published: The Japan Society of Mechanical Engineers 2022
• Subjects: Axis–switching; Flow control; Flow measurement; Flow visualization; Jet spread; Rectangular jet; Tapered triangular tube; Vorticity
• ISSN: 2187-9761
• DOI: 10.1299/transjsme.21-00275

The purpose of this study is to clarify the effect of the tapered triangular tubes added to the four corners of a 2:1 rectangular nozzle on the flow characteristics and vortical structures of a rectangular jet. The angles of tapered triangular tubes were changed α = +6° and −6°. The mean bulk velocity U0 from the nozzle exit was about 4.5 m/s. The Reynolds number Re (= U0H/ν; ν, kinematic viscosity of air) of the jet was 9,000. In the case of the jet without tapered triangular tubes, the three–dimensional deformation of the vortex ring produces strong positive and negative vorticity around each axis and also increases the turbulent kinetic energy at the jet corners. The spread of the jet is larger than that of other jets. In the case of jet with divergent tapered triangular tubes with α = +6°, the local vorticity and turbulent kinetic energy increase at the corners of the jet were suppressed and the profile followed the jet shape. As a result, the jet becomes a circular jet shape until relatively downstream, and the jet spread was smaller than that of the other jets. On the other hand, in the case of the jet with convergent tapered triangular tubes with α = −6°, the jet maintains a relatively rectangular jet shape upstream due to the local increase in vorticity on the long side of the nozzle and the increase in turbulent kinetic energy along the nozzle shape. However, the overall spread of the jet is almost the same as that without the tapered triangle tubes due to the diffusion of the jet along the nozzle span length. Therefore, it is possible to change the flow characteristics and vortical structures of the rectangular jet by adding tapered triangular tubes with different angles.