Author(s)

S. Fujita, T. Harima & H. Osaka

Abstract

The mean velocity field of turbulent air jets issuing from a rectangular nozzle (AR: Aspect Ratio=12.5) with a rectangular notch at the midspan have been investigated experimentally. The four notch aspect ratios (NAR) of the rectangular notch perpendicular to the rectangular nozzle axis are 2.5, 7.5, 12.5 and 165. The purpose of this study is to examine the possibility of manipulating the mean velocity field of the rectangular jet using the rectangular notch as a passive disturbance. In this experiment, it is revealed that the inward secondary flow velocities towards the jet centre region on both the rectangular jet axis and the rectangular notch axis in the upstream region are found in all NAR cases, and both the magnitude and the direction of the secondary flow velocity depend on the value of NAR. Furthermore, the potential core length of NAR=12.5 takes the largest value in all NAR cases. The half velocity width on the rectangular jet axis takes the minimum value for NAR=165. Keywords: rectangular jet, rectangular notch, passive control, mean velocity field, secondary flow, streamwise development. 1 Introduction The rectangular jet is very useful in many cases for which the improvement of the entrainment rate or the promotion of mixing is necessary. However, in the case of the employment of the rectangular jet to the engineering field, the elongation of the jet flow is expected in many industrial cases, for example, washing by multiple parallel jets, the uniformity plating technique, the acid washing process of rolling mill and the air curtain (air shield and ventilating).

Keywords

rectangular jet, rectangular notch, passive control, mean velocity field, secondary flow, streamwise development.