Séminaire exceptionnel IUSTI – 7 déc. 2023 – 11h salle 250

Investigation of unsteady secondary flows and large-scale turbulence in heterogeneous turbulent boundary layers

Dea Daniella Wangsawijaya – Univ. of Southampton, UK

The nature of wall-bounded turbulent flows over rough surfaces, whose roughness distribution is homogeneous, has been studied extensively and is relatively well defined. Most surfaces in nature and engineering applications, however, are heterogeneous and the heterogeneity can be arranged in an infinite number of ways. Examples include: rivets on aircraft, bio-fouling on ships, sedimentation on riverbeds, and forest and crop boundaries in the atmospheric surface layer. This talk will focus on a specific roughness arrangement composed of spanwise-alternating smooth and rough strips. Embedded within the turbulent boundary layer developing over such surface are secondary flows in the form of counter-rotating streamwise vortices. Instantaneously, these secondary flows are visually similar to the large-scale motions (LSMs/VLSMs) that occur naturally over smooth walls – both appear as elongated high- and low-momentum streaks. In this talk, I will investigate parameters affecting the formation of the secondary flows and take a closer look at the structures of turbulence in roughness-induced secondary flows, and how these structures compare to the naturally occurring LSMs/VLSMs.