Investigation of the Development of Localized Disturbances in the Boundary Layer of a Flat Plate under Conditions of Moderate Degree of the Incoming Flow Turbulence behind the Surface Step

Abstract
In a wind tunnel on a flat plate in a separated flow behind a rectangular step, the emergence and development of localized disturbances generated by low-frequency impulse deviations of the local surface section under conditions of low and moderate degrees of the incoming flow turbulence is studied. The results were obtained by hot-wire anemometry at low subsonic flow velocity. It was found that impulse deviations of the wall generate disturbances, which are socalled Streaky structures and wave packets of oscillations. The separation of the laminar boundary layer accelerates the growth of wave packets with subsequent turbulization of the near-wall flow. The specific features of the behavior of localized disturbances under conditions of moderate degree of free-stream turbulence are revealed.

Keywords
boundary layer, flow separation, transition to turbulence, streaky structures, wave packets, moderate free-stream turbulence level
Funding
This work was partially carried out within the framework of the Program of Basic Scientific Research of State Academies of Sciences for 2013–2020 (project AAAA-A17-117030610128-8) and with state support for scientific research conducted under the guidance of leading scientists in Russian universities, agreement No. 075-15-2019-1923
УДК 532.526

Investigation of the Development of Localized Disturbances in the Boundary Layer of a Flat Plate under Conditions of Moderate Degree of the Incoming Flow Turbulence behind the Surface Step