Turbulent Prandtl Number in Neutrally Buoyant Turbulent Round Jet

A method which combines two nonintrusive imaging techniques, particle tracking velocimetry and laser induced fluorescence, was used to make simultaneous measurements of velocity and concentration in a neutrally buoyant turbulent round jet. The measurements were made at two different Reynolds numbers (R), 360 and 4,210, at a Schmidt number of 1,930. The mean velocity 〈u〉, mean concentration 〈c〉, Reynolds stress -〈u′v′〉, and turbulent scalar flux 〈v′c′〉 were obtained and the eddy viscosity, eddy diffusivity, and turbulent Prandtl number (Prt) calculated from these measurements. Both the low and high Reynolds number results show self-similar characteristics that are dependent on R with Prt a function of radial position. For the R=4,210 case, it was found that 0.7 0.12. For the R=360 case, it was found that Prt≈0.4 for 0.06<y/x<0.15 but significantly smaller at the center (approximately half of the peak value) and outer regions of the jet profile. Comparatively, for the R=4,210 case, Prt at y/x=0 is only slightly smaller than the peak value (0.7 versus 0.9). In both R cases, the maximum of Prt occurred at approximately y/x=0.1.