Turbulence structural measurements using a comprehensive laser-Doppler velocimeter in two- and three-dimensional turbulent boundary layers

The advanced 'comprehensive' laser-Doppler velocimeter is used to acquire spatially and temporally resolved turbulence structural measurements in high Reynolds number two- and three-dimensional turbulent boundary layers. The new instrument directly measures three-dimensional particle trajectories at high repetitions. These trajectories are analyzed in post-processing to obtain fluctuating velocity gradient tensor fields, which lead to direct measurements of turbulent viscous dissipation rates. Such data acquired in two- and three-dimensional boundary layers with an approach flow momentum thickness Reynolds number, Reθ = 7500 are presented. Results indicate that anisotropy of the dissipation rate of Reynolds stresses persists to similar heights in viscous wall units as obtained with direct numerical simulations at lower Reynolds numbers. Measurements in a three-dimensional turbulent boundary layer in the vicinity of a wing/body junction also indicate that a reduction in the value of the velocity/pressure-gradient correlations for the Reynolds normal stresses reduces the turbulent energy redistribution and contributes to reduced shear stress magnitudes, as observed previously through DNS (Moin, P., Shih, T.-H., Driver, D., Mansour, N.N., 1990. Direct numerical simulation of a three-dimensional turbulent boundary layer, Phys. Fluids A 2 (10), 1846-1853).