The flowfield of the three-dimensional jet issuing from a rectangular nozzle (aspect ratio: AR=12.5) with a rectangular notch (AR=2.5, 7.5 and 12.5) at the midspan were examined experimentally. The aim of this study is to examine the control of the mixing and diffusion processes of the flowfield of a rectangular jet using a rectangular notch. Measurements were made using an X-type hot-wire prove, linearized constant temperature anemometers and a five holes pitot static pressure tube. In this experiment, the Reynolds number was kept constant 30000 (notch AR=2.5 and 7.5) and 15000 (notch AR=12.5). From the results, the followings were clarified. The potential core length for the case of notch AR=12.5 took the maximum value in all notch AR. Furthermore, the entrainment rate showed the maximum value for the case of notch AR=12.5.
