NONISOTHERMAL TURBULENT BOUNDARY-LAYER ADVERSE PRESSURE-GRADIENT LARGE-SCALE THERMAL STRUCTURE MEASUREMENTS

Hot-wire anemometry measurements in an incompressible turbulent boundary-layer now over a heated flat plate under equilibrium adverse-pressure-gradient conditions (beta = 1.8) were made for two different temperature difference cases (10 and 15-degrees-C) between the wall and the freestream. Space-time correlations of temperature fluctuations (T') were obtained with a pair of subminiature temperature nuctuation probes. The mean convection velocities, the mean inclination angles, and coherence characteristics of the T' large-scale structure were determined. The present temperature structures measurements for a nonisothermal boundary layer are compared to the zero-pressure-gradient case with identical temperature differences previously reported, in which the mean convection velocity of the T' structure was a function of position y+ and independent of the limited temperature-difference cases tested. The three major findings of the present study, as compared to the zero-pressure-gradient case, are 1) the mean convection speed of the T' structure under beta = 1.8 pressure-gradient conditions was found to be substantially lower in the logarithmic core region than the zero-pressure-gradient case. Additionally, the mean convection speed is felt by the authors to be a function of pressure-gradient parameter beta; 2) the mean inclination angle of the T' structure to the wall under the adverse-pressure-gradient flow was 32 deg, which compares favorably to the 30-deg value of the zero-pressure-gradient case; and 3) the limited data suggests that the mean convection velocity of the T' structure is a function of y+ and independent of the limited temperature-difference cases tested.