Dynamic of turbulent kinetic energy advection in an unsteady separated turbulent boundary layer

Abstract

Advection of separation bubbles occurs in many engineering applications such as pitching and plunging airfoils, wake-rotor interaction, and stalled diffusers. In all these cases, unsteady separation is generated by a space- and time-varying pressure gradient, and the resulting separation bubble is then advected downstream. A similar behavior was observed in the numerical study by Ambrogi et al. (2022), in which the Large-Eddy simulation technique was used to investigate the effects of unsteady flow separation on the flow physics of a turbulent bounday layer. Several reduced frequencies $k$, ranging from a very rapid flutter-like motion to a quasi-steady flapping, have been investigated. The advection of the separation bubble was only observed for a specific reduced frequency $k=1$ at which the convective timescale of the flow is comparable to the unsteady imposed timescale. The purpose of the present work is to investigate the dynamics of such advection process by analyzing the effects of unsteady separation on Turbulent Kinetic Energy and Reynolds stresses.