Uniform momentum zones (UMZs) for an adverse pressure gradient turbulent boundary layer (APG-TBL) are characterised in this paper.The database described by Cuvier et al.(2017), which was obtained using 2-component 2-dimensional (2C-2D) particle image velocimetry (PIV) at two free-stream velocities of 5 m/s and 9 m/s, is used for this study.The methodology described by Adrian et al.(2000) is used to identify and hence, statistically characterise the UMZs and UMZ interfaces in the APG-TBL. This study shows that the number of detected UMZs increases in the streamwise direction for both free-stream velocities.This increase is primarily thought to be due to the adverse pressure gradient (APG) since a comparison of the results between the two free-stream velocity APG-TBLs did not show any statistically significant difference with Reθ for the range of Reynolds number examined in this study.The thickness of the UMZs, δw and the jump in streamwise velocity across the UMZ interface were found to increase in the wall-normal direction, whereas the width of the UMZ interface, Δu, was found to decrease.The number of UMZs, Numz, identified appeared to influence the modal velocities/uniform velocities, geometrical properties of the UMZs and statistics of the flow.With increasing Numz, the modal velocities of the UMZs moved to higher values to accommodate new UMZs that developed closer to the wall and the thickness of each UMZ andΔu across the UMZ interface decreased, whereas δw increased. A slight difference in the magnitude of streamwise Reynolds stress and Reynolds shear stress was observed in the inner and outer regions, and a slight difference in the magnitude of turbulence production was also observed in the inner region between the velocity fields having a low or high number of UMZs indicating that the flow statistics are influenced by the number of UMZs present in the APG-TBL.
|Number of pages||20|
|Journal||Experimental Thermal and Fluid Science|
|Publication status||Published - 1 Jul 2020|