Spatio-temporal development of wall pressure events in turbulent wall-bounded flow

The wall pressure field from a direct numerical simulation of turbulent channel flow was used for the conditional detection of wall pressure peak events and wall pressure gradient events resulting in a space and time record of the evolution of such events. Wall pressure peak events have regions of pressure of the opposite sign just upstream and downstream of them. Favorable and adverse pressure gradient events occur in conjunction with sharp positive and negative peaks in the wall pressure. All events extend 130 to 200 wall units in the streamwise direction and about 70 to 100 wall units in the spanwise direction. Events begin as a traveling cluster of two or three waves in the wall pressure. The entire event lasts 60 to 75 ν/U_τ² and convects over a streamwise distance of 800 to 950 ν/U_τ. Both the spectral energy and wavenumber of the wave cluster increase as the event grows and decrease as the event decays. Based on a comparison of these different types of events, the 'characteristic' wall pressure event in a turbulent boundary layer appears to be a negative wall pressure peak upstream of a positive wall pressure peak with an adverse pressure gradient between the peaks. Since the adverse pressure gradient likely corresponds to the local inflectional velocity profile associated with the burst cycle, the characteristic wall pressure signature can be related to the lifting up of a horseshoe vortex and the shear layer of the burst cycle.