Turbulent Jets Issuing from Rectangular Nozzle with a Rectangular Notch at the Midspan

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) 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. From this experiment, it was revealed that the attachment of the rectangular notch to the rectangular jet restrained the increase of the turbulent velocity scales in the cases of NAR≥7.5. The principal strain rate Sxy on the y axis in the cases of NAR≤2.5 indicated the direct contribution to the production of the turbulent kinetic energy near the jet center in the upstream region, however, the development of the turbulent velocity in the cases of 7.5≤NAR≤12.5 was suppressed because of Sxy=0. Furthermore, the extra strain rate Szz caused by the secondary flow on the z axis contributed to the production of the turbulent kinetic energy near the jet center in the upstream region, and the other extra strain rate Syy on the y axis contributed to the suppression of the turbulent velocity.