Wall-pressure fluctuations in an axisymmetric boundary layer under strong adverse pressure gradient

Measurements of fluctuating wall pressure in a high-Reynolds-number flow over body revolution are described. With strong axial gradient and moderate lateral curvature, this non-equilibrium is relevant to marine applications as well short-haul urban transportation. The wall-pressure spectrum its scaling discussed, along with relation the space–time structure. As decelerates downstream, root-mean-square level drops together shear stress ( $\tau _w$ ) consistently approximately 7 . While associated dimensional spectra see broadband reduction 15 dB per Hz, they appear attain single functional form, collapsing within 2 when normalized wall-wake where scale $U_e/\delta$ frequency scale. Here, $\delta$ boundary layer thickness $U_e$ local free-stream velocity. general success scaling, including viscous $f^{-5}$ region, suggests that large-scale motions outer play predominant role near-wall turbulence pressure. On investigating further, we find instantaneous fluctuations characterized by quasi-periodic feature appears convect downstream at speeds consistent peak stresses. conditional structure feature, estimated through detection time series, resembles roller, supporting embedded hypothesis (Schatzman & Thomas, J. Fluid Mech. , vol. 815, 2017, pp. 592–642; Balantrapu et al. 929, 2021, A9). Therefore, outer-region shear-layer-type may be important devising strategies for control, drag noise decelerating layers.