Investigation of large scale motions in zero and adverse pressure gradient turbulent boundary layers using high-spatial-resolution particle image velocimetry

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 Laboratoire de Mécanique des Fluides Lille (LMFL) High Reynolds number Boundary Layer Wind Tunnel. The ZPG-TBL has momentum-thickness based R e δ 2 = U ∕ ν 7 , 750 (where is momentum thickness edge velocity), while APG-TBL 16 240 Clauser’s pressure gradient parameter β 1 P x τ w . 27 displacement thickness, streamwise direction wall shear stress). 2C fluctuating flow field each TBL was decomposed using proper orthogonal decomposition (POD) to investigate large-scale motions (LSMs). LSMs are found be energized outer-layer, becoming stronger presence adverse-pressure-gradient. Profiles conditionally averaged stresses show that high-momentum contribute more than low-momentum from end log-layer opposite wake region. cross-over point between profiles high- always higher value corresponding stress unconditional ensemble average at same wall-normal location. This difference up 80% 15% stresses. Furthermore, further ZPG-TBL. conditional without reduced by 42% 50% APG-TBL, having minimal effect on both ZPG- APG-TBL. • Large scale (LSMs) have been investigated high Proper used identify large motions. outer region layer. contributions larger log smaller amplified APG.