Morphology and Dynamics of Wall-Pressure Extrema in Wall-Bounded Turbulence

The surface pressure in wall-bounded turbulent flows exhibits extreme localized variations in both time and space. Such fluctuations are highly intermittent, with a pronounced flatness in their distribution, indicating a strong contribution from the extrema in wall-pressure statistics. We present a physical interpretation of the relationship between the pressure extrema and velocity and vorticity coherent structures found in the near-wall region, using direct numerical simulation (DNS) of turbulent channel flows at Reτ = 180 − 5200. A combination of Lagrangian tracking and Eulerian statistics is used to examine the morphological and temporal properties of these extreme events. The results reveal a Reynolds-number dependence in the lifespan and orientation of these structures with respect to the freestream. Tracking of the positive-gauge pressure extrema reveals a link to pairs of streamwise vorticity structures straddling the peaks. The temporal correlation between pressure and streamwise vorticity is also explored to determine the direction of causality between these coherent structures found in boundary layer flows.