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EFFECTS OF NOZZLE PERTURBATIONS ON TURBULENT MIXING IN IMPINGING JETS

Rong Ding
Department of Heat and Power Engineering, Lund Institute of Technology P.O. Box-1I8, Lund 22100, Sweden

Johan Revstedt
Division of Fluid Mechanics, Lund Institute of Technology P.O. Box 118, S-221 00 Lund, Sweden

Laszlo Fuchs
Department of Mechanics, KTH, CICERO, SE-10044 Stockholm; Division of Fluid Mechanics Lund University Lund, 22363, Sweden

Abstract

The effect of the perturbations at the jet nozzle on the turbulent mixing in impinging jets is studied using simultaneous Particle Image Velocimetry (PIV) and Planar Laser-induced Fluorescence (PLIF) technique. The nozzle-to-wall distance H/D = 5.0 is investigated for turbulent jet flows at a Reynolds number of 6,000. The jet exit conditions are examined and typical flow structures in the jet are demonstrated. The unperturbed nozzle (N-O) is compared to nozzles with two (N-2) and three (N-3) needle shaped rods, respectively. The results show that the potential core is shorter in the N-2 and N-3 cases. This is caused by an earlier transition to turbulence and wider distribution of vorticity in the shear layer, which also leads to enhanced mixing indicated by the evolution of the dye tracer and the turbulent fluxes. The effect of the perturbation is also evident in other statistical properties, such as turbulent kinetic energy.