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

Shigetaka Fujita,Takashi Harima,Hideo Osaka

doi:10.1051/epjconf/20122501017

Shigetaka Fujita, Takashi Harima + Show 1 more

Open Access

https://doi.org/10.1051/epjconf/20122501017

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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.

Highlights

The rectangular jet is very useful in many cases of which the improvement of the entrainment rate or the promotion of mixing is necessary
It is found that the attachment of rectangular notch perpendicular to the rectangular nozzle suppresses the development of turbulent velocity scales near the jet centre in the upstream region
It follows from what has been said that the attachment of the rectangular notch perpendicular to the rectangular nozzle suppresses the development of the turbulent kinetic energy near the jet centre in the upstream region, and the magnitude of the suppression effect depends on the value of NAR

Summary

Introduction

The rectangular jet is very useful in many cases of which the improvement of the entrainment rate or the promotion of mixing is necessary. In case of the employment of the rectangular jet to engineering fields, the elongation of the high velocity jet flow region is expected in many cases, for example, the uniformity plating technique and the air curtain (air shield and ventilating). Trentacoste and Sforza [1], and Sforza and Stasi [2] classified the flowfield of the rectangular jet into 3 regions (Potential Core region (PC region), Characteristic Decay region (CD region) and Axisymmetric Decay region (AD region))

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