Simultaneous velocity and passive scalar concentration measurements in low Reynolds number neutrally buoyant turbulent round jets

Velocity and scalar concentration characteristics of low Reynolds number (Re) neutrally buoyant turbulent round jets were studied using coupled particle image velocimetry and laser induced fluorescence. Experiments were conducted on a jet with a fully developed pipe exit profile at Re = 1,500 and Re = 4,000. Measurements were made in the far field (60 < x/D < 80). Results show that the centerline velocity decay constant increases with Re and the virtual origin is located far from the jet exit. The Re does not have such an influence on the scalar concentration decay constant and scalar field virtual origin. Centerline turbulent intensities show evidence of becoming self-similar past x/D ≈ 75 but the same is not observed in the scalar fluctuations. The latter are strongly influenced by the Re, increasing as entrainment of ambient flow on the jet axis increases as the flow approaches laminar conditions. Scalar fluxes showed a marked Re dependence as well. Results were used to estimate the turbulent Schmidt number which decreases as the Re decreases. © 2007 Springer-Verlag.