Turbulence Structure in Non-zero Pressure Gradient Boundary Layers

Experimental measurements were made in non-equilibrium boundary layers on a smooth wall. In the test section, a zero pressure gradient (ZPG) development region was followed by a favorable pressure gradient (FPG) with constant acceleration parameter K, a ZPG recovery region, and an adverse pressure gradient region with constant K. The acceleration rates were as high as K=2×10^-6 in the FPG and -1×10^-6 in the APG. Velocity profiles were acquired at 12 streamwise stations using LDV. Velocity field measurements were acquired at the same locations using PIV in the streamwise-wall normal plane and two streamwise-spanwise planes at y/δ=0.15 and 0.4. Turbulence statistics, two point correlations of various turbulence quantities, and linear stochastic estimation were used to analyze the data. Strong FPG caused deviation from the law of the wall, suppression of the wake, significant lengthening of structures in the streamwise direction, and a reduction of inclination angles with respect to the wall. The ZPG recovery was rapid. APG behavior was opposite to the FPG with strong growth of the wake, but less pronounced dimensionless changes in the correlations.