MEASUREMENTS OF TURBULENT BOUNDARY-LAYER PRANDTL NUMBERS AND SPACE-TIME TEMPERATURE CORRELATIONS

Hot-wire anemometry measurements in an incompressible turbulent boundary-layer flow over a heated flat plate at zero pressure gradient were made using an x probe and a temperature fluctuation probe. The measurements were made for three different temperature difference cases between the wall and the freestream 10, 15, and 20-degrees-C. Simultaneous measurements of the two components of the velocity and the temperature were made at the same point using an x probe and a temperature fluctuation probe. The experiments resulted in direct measurement of the turbulent Prandtl number as a function of height through the boundary layer for the three temperature difference cases. Also, space-time correlations of temperature fluctuations T' were obtained with a pair of temperature fluctuation probes. The mean convection velocities of the T' large-scale structure are presented for the three temperature difference-cases. The mean convection velocity of the T' structure is a function of position y+ and was found to be independent of the temperature difference for the cases considered. The convection velocity varied from 0.65 infinity at the smallest measured value of y+ = 75 to about 0.77u infinity at y+ = 425, the largest measured value of y+ .