Large Amplitude Wall Pressure Events Beneath a Turbulent Boundary Layer

Abstract

Experimental data on the temporal records of the wall pressure fluctuations beneath a turbulent boundary layer have been acquired in a low-noise flow facility. The pressure data were first analyzed using long-time averaging techniques to determine the statistical properties and the results were compared to the baseline data of Scheme (1983). Next, the pressure records were conditionally sampled at various k threshold levels (p′w ≥ k·Prms) to detect large amplitude, positive and negative events which were then averaged and analyzed to determine their shape, duration, and frequency of occurrence. The intermittent large amplitude events are very short in duration, occur rather infrequently in time, but are a major contributor to the high frequency content of the wall pressure fluctuations. As an example, events where p′w ≥ |3·prms| have an average duration of 14 viscous time units, occur 5 percent of the time and contribute 49 percent to the RMS value. The time between events appears to have a lognormal statistical distribution. The frequency of occurrence of the large amplitude events are consistent with the burst rate for flow structures and thus support the conjecture that the large amplitude events are associated with the near-wall bursting process.