Study of the motions contributing to the Reynolds stress in high and low Reynolds number turbulent boundary layers

Physical experiments are used to explore the properties of the motions contributing to the Reynolds stresses in high and low Reynolds number turbulent boundary layers. The low Reynolds number smooth wall measurements (R-theta=1010, R-theta=2870, and R-theta=4850) were acquired in a large-scale low speed wind tunnel, while the high Reynolds number measurements [R(theta)similar toO(10(6))] were acquired at the Surface Layer Turbulence and Environmental Science Test site, Dugway, Utah. These high Reynolds number turbulent boundary layer data were acquired over nearly hydraulically smooth and rough walls. At each Reynolds number and surface roughness, data comparisons were made at approximately y(p)/2 and 2y(p), where y(p) is the peak position of the Reynolds shear stress. Scale separation effects associated with increasing R-theta are analyzed via spectral measurements (u, v, and u-v cospectra), and by segregating the streamwise and wall-normal velocities according to their frequency content using simultaneous high- and low-pass filtering. A primary observation is that the predominant motions underlying the stress undergo a significant shift from large to intermediate scales as R-theta becomes large, irrespective of surface roughness. Quadrant analysis of the filtered signals is employed to clarify the correlated scales involved in the generation of the stress. Overall, it is apparent that the types of motions contributing to Reynolds stress undergo significant variations at comparable wall-normal locations (relative to y(p)) over the Reynolds number range explored. (C) American Institute of Physics.