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This study uses high-fidelity simulations (DNS or LES) and experimentaldatasets to analyse the effect of non-equilibrium streamwise mean pressuregradients (adverse or favourable), including attached and separated flows, onthe statistics of boundary layer wall-pressure fluctuations. The datasetscollected span a wide range of Reynolds numbers ($Re_\theta$ from 300 to23,400) and pressure gradients (Clauser parameter from $-0.5$ to 200). Thedatasets are used to identify an optimal set of variables to scale the wallpressure spectrum: edge velocity, boundary layer thickness, and the peakmagnitude of Reynolds shear stress. Using the present datasets, existingsemi-empirical models of wall-pressure spectrum are shown unable to captureeffects of strong, non-equilibrium adverse pressure gradients, due toinappropriate scaling of wall pressure using wall shear stress, calibrationwith limited types of flows, and dependency on model parameters based onfriction velocity, which reduces to zero at the detachment point. To addressthese short-comings, a generalized wall-pressure spectral model is developedwith parameters that characterize the extent of the logarithmic layer and thestrength of the wake. Derived from the local mean velocity profile, these twoparameters inherently carry effect of the Reynolds number, as well as those ofthe non-equilibrium pressure gradient and its history. Comparison with existingmodels shows that the proposed model behaves well and is more accurate instrong-pressure-gradient flows and in separated-flow regions.

A generalized wall-pressure spectral model for non-equilibrium boundary layers