Velocity-Concentration Joint Statistics for the Diffusion Field of Passive Scalar Substance in a Round Jet Discharging into Uniform Counter-Flow

Abstract

Simultaneous measurements on the velocity and concentration fields of matter in a turbulent round jet injected into a counter stream have been conducted by using a combined system of PIV and PLIF techniques. Experiments were carried out for four cases of jet to counter-flow velocity ratios: V_r = 2.4, 3.4, 5.5 and 7.8. Axial profiles of the concentration statistics along the jet centerline showed that both rms concentration fluctuation and streamwise turbulent flux of mass have two peaks in the near field of the jet and in the mean stagnant region. The radial flux was found to have an tendency to increase in an off-axis area outside the dividing streamline due to a circumferential wandering of the jet about the axis. These features for the axial and radial mass fluxes appeared more obviously as Vr decreased. By investigating the joint PDF between axial velocity and concentration, it was confirmed that alternate streamwise transport of dyed fluid in the jet and ambient fluid in the counter-flow is related with the enhancement in the streamwise turbulent flux of mass in the stagnant region.