Turbulent jets issuing from rectangular nozzle with a rectangular notch at the midspan

¹ Department of Mechanical and Electrical Engineering, Tokuyama College of Technology, Gakuendai, Shunan, Yamaguchi, 745-8585, Japan
fujita@tokuyama.ac.jp ; harima@tokuyama.ac.jp
² Department of Mechanical System, Hiroshima Institute of Technology, Miyake, Saekiku, Hiroshima, Hiroshima, 731-5193, Japan
h.ohsaka.xv@it-hiroshima.ac.jp

Abstract

The turbulent flowfield of turbulent jet issuing from rectangular nozzle (Aspect Ratio=12.5) with a rectangular notch at the midspan, has been investigated experimentally. Four aspect ratios of rectangular notch (NAR: Notch Aspect Ratio) used in this experiment were 2.5, 7.5, 12.5 and 165. The Reynolds number based on the nozzle width d and the exit mean velocity Ue, was kept constant 30000 (NAR=2.5 and 7.5), 15000 (NAR=12.5) and 13000 (NAR=165), respectively. Longitudinal mean velocity and turbulent intensities were measured using an X-array Hot-Wire Probe (5 µm in diameter, 1 mm effective length) operated by the linearized constant temperature anemometers (DANTEC), and the spanwise and the lateral mean velocities were measured using a yaw meter. The signals from the anemometers were passed through the low-pass filters and sampled using A.D. converter. The processing of the signals was made by a personal computer. Acquisition time of the signals was usually 80 seconds. From this experiment, it was revealed that the attachment of a rectangular notch to the rectangular jet suppressed the development of the turbulent velocity scales near the jet centre in the upstream region for the cases of NAR≥7.5.