Multifractality and versatility of the intermittency of wall pressure fluctuations in a turbulent boundary layer

Digitized recordings of pressure traces are used to analyze the intermittency of wall pressure fluctuations in a turbulent boundary layer (TBL) of a pipe flow. The intermittency manifests itself by pressure bursts of abnormally high amplitude, which have a more complex structure than a pulse random process with independent intervals. The moments of sampled mean squares of pressure fluctuations are examined as functions of the averaging time. The scaling properties of these moments are determined for the averaging time varying over intervals exceeding the correlation time of the process. The scaling exponents and dimensionless boundaries of the scaling intervals, based on the values of flow velocity and TBL thickness, are found to be equal for all flow regimes examined. This equality indicates that the intermittency of pressure fluctuations is due to the intermittent nature of turbulent energy production during the development of coherent structures (turbulent bursts) in the TBL. The upper boundaries of the scaling intervals, normalized to the average interval between turbulent bursts, are close to unity, being equal for different values of the flow velocity and boundary layer thickness. The moment scaling is interpreted in terms of a multifractal model. A multifractal spectrum of the process, universally applicable to all flow regimes, is obtained.