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 (Pr-t) calculated from these measurements. Both the low and high Reynolds number results show self-similar characteristics that are dependent on R with Pr-t a function of radial position. For the R=4,210 case, it was found that 0.7<Pr-t<0.9 for 0<y/x<0.15 (y is the radial coordinate and x the streamwise coordinate) with Pr-t decreasing monotonically for y/x>0.12. For the R=360 case, it was found that Pr(t)approximate to0.4 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, Pr-t at y/x=0 is only slightly smaller than the peak value (0.7 versus 0.9). In both R cases, the maximum of Pr-t occurred at approximately y/x=0.1.