Longitudinal Vortices in Turbulent Boundary Layers Subjected to Wall Curvature and Strong Adverse Pressure Gradients: Numerical Investigations Using LES and DNS

Abstract

Abstract : Longitudinal vortices in turbulent boundary layers that are subjected to strong wall curvature (both convex and concave) and strong adverse pressure gradients were investigated numerically. The motivation for this research was to uncover the fundamental mechanisms responsible for the generation of longitudinal vortices and their dynamical interaction with the other dominant coherent structures that arise from the presence of wall curvature and strong adverse pressure gradients. This understanding is essential for future implementation of separation control techniques for practical flows when longitudinal vortices are inherently present, or when forced longitudinal vortices are employed for separation control (i.e., on demand vortex generators). Furthermore, such investigations can shed light on the turbulence generation mechanisms for boundary layers subjected to streamwise curvature and pressure gradients when longitudinal vortices are present. The investigations were carried out using DNS, LES and unsteady RANS. Towards this end, we have employed our new Flow Simulation Methodology (FSM) for calculating turbulent flows. The present numerical investigations were a critical test for FSM and the turbulence model used in FSM as the investigated flows are highly complex with the turbulence in strong non-equilibrium.