VELOCITY AND WALL PRESSURE FLUCTUATIONS OF TURBULENT BOUNDARY LAYER

The results of the study of the velocity pulsation field and the near-wall pressure of the turbulent boundary layer, which is formed on a flexible elongated cylinder and a hydraulically smooth flat plate, are presented. Peculiarities of the interaction of the velocity and pressure fields in the boundary layer are shown; sound and pseudosonic sources of hydrodynamic noise are characterized. The integral, correlation and spectral characteristics of the field of velocity pulsations and wall pressure in the turbulent boundary layer are analyzed. The relationship between these statistical characteristics is shown, as well as the mechanisms and sources that influence the behavior of these characteristics. It is noted that large-scale vortex structures and small-scale vortices are formed in the turbulent boundary layer, which form the outer and inner regions of the boundary layer. It is established that large-scale vortex structures generate pressure fluctuations, whose probability density distribution law is close to Gaussian law, and small-scale vortices that generate high-frequency or low-wave fluctuations have a non-Gaussian law of probability distribution of pulsation density. The interaction of coherent vortex structures with each other and with the streamlined surface leads to changes in the integral, correlation and spectral characteristics of the velocity and pressure fields. It is noted that with increasing the distance between the pressure fluctuation sensors, the correlation of signals decreases, and the delay time of correlated signals increases. Thus, with the increasing of the distance between the measuring points, the correlated fluctuations are those generated by the large-scale vortex structures. It is determined that the highest levels of velocity and pressure fluctuations are generated by the large-scale vortex structures that have the highest coherence. The results obtained make it possible to characterize coherent vortex structures, their features of formation, places of origin, scales, directions and velocities of transfer.