  High-spatial-resolution (HSR) two-component, two-dimensional
particle-image-velocimetry (2C-2D PIV) measurements of a zero-pressure-gradient
(ZPG) turbulent boundary layer (TBL) and an adverse-pressure-gradient (APG)-TBL
were taken in the LMFL High Reynolds number Boundary Layer Wind Tunnel. The
ZPG-TBL has a momentum-thickness based Reynolds number $Re_{\delta_2} =
\delta_2 U_e/\nu = 7,750$ while the APG-TBL has a $Re_{\delta_2} = 16,240$ and
a Clauser's pressure gradient parameter $\beta = \delta_1 P_x/\tau_w = 2.27$
After analysing the single-exposed PIV image data using a multigrid/multipass
digital PIV (Soria, 1996) with in-house software, proper orthogonal
decomposition (POD) was performed on the data to separate flow-fields into
large- and small-scale motions (LSMs and SSMs), with the LSMs further
categorized into high- and low-momentum events. Profiles of the conditionally
averaged Reynolds stresses show that the high-momentum events contribute more
to the Reynolds stresses than the low-momentum between wall to the end of the
log-layer and the opposite is the case in the wake region. The cross-over point
of the profiles of the Reynolds stresses from the high- and low-momentum LSMs
always has a higher value than the corresponding Reynolds stress from the
original ensemble at the same wall-normal location. Furthermore, the cross-over
point in the APG-TBL moves further from the wall than in the ZPG-TBL. By
removing the velocity fields with LSMs, the estimate of the Reynolds streamwise
stress and Reynolds shear stress from the remaining velocity fields is reduced
by up to $42 \%$ in the ZPG-TBL. The reduction effect is observed to be even
larger (up to $50\%$) in the APG-TBL. However, the removal of these LSMs has a
minimal effect on the Reynolds wall-normal stress in both the ZPG- and APG-TBL.
