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This paper provides an experimental investigation on the internal shear layers and the edges of the uniform momentum zones (UMZs) in a turbulent pipe flow. The time-resolved stereoscopic particle image velocimetry data are acquired in the cross-section of the pipe, and span the range of Reynolds number . In the first part of the study, internal shear layers are detected using a three-dimensional detection method, and both their geometry as well as their fingerprint in the flow statistics are examined. Three-dimensional conditional mean flow analysis revealed a strong low-speed region beneath the average shear layers. This low-speed region is associated with positive wall-normal fluctuations, and it is accompanied by two swirling motions having opposite signs on either side in the azimuthal direction. Moreover, the shear layers are stretched by the two opposite azimuthal motions. In the second part of the study, the shear layers are treated as the continuous edges of the UMZs, which are detected using the histogram method following Adrian et al. (J. Fluid Mech., vol. 422, 2000, pp. 1-54) and de Silva et al. (J. Fluid Mech., vol. 786, 2016, pp. 309-331). For this part, two different orientation of the planes are used, i.e. the wall-normal-streamwise plane and the wall-normal-spanwise plane (cross-section of the pipe). Comparison of the detected structures shows that the shear layers mostly overlap with a UMZ edge (in either plane).

This experimental study proposes a master-slave fluidic oscillator that can produce sweeping impinging jets with adjustable spreading angles. The flow fields of the jet impingement on convex cylinders are measured using time-resolved particle image velocimetry (TR-PIV) in a water tank. By increasing the proportion of the flow rate that passes through the master layer from 0 to 1 (master flow rate, MFR), the range of the jet spreading angle can be smoothly increased from 0 degrees to about 100 degrees. This new design is then applied in impingement upon two convex cylinders with different diameters. The large cylinder has a diameter of D/D-h = 12.5, where D-h is the hydraulic diameter of the jet exit. When the jet spreading angle is maximized by setting MFR = 1, the jet can cover half of the large cylinder. On the other hand, for the small cylinder with a diameter of D/D-h = 2.5, the jet can enclose the whole convex surface when the jet spreading angle is minimized at MFR = 0. In addition, proper orthogonal decomposition (POD) analysis reveals different unsteady flow patterns induced by the jet interaction with the cylinders. This study demonstrates, very first time, flexibility of the novel sweeping jet oscillator and guides towards some potential applications. (C) 2020 Elsevier Masson SAS. All rights reserved.