Effects of streamline curvature on a turbulent boundary layer

Flow around marine and aerial vehicles often exhibits three-dimensional turbulent boundary layers with streamline curvature, the effects of which are still not fully understood. To this end, direct numerical simulation is performed to study the independent effects of spanwise and convex curvature on transitioning and turbulent boundary layers. Turbulent transition is induced with an array of resolved cuboids, and spanwise curvature is prescribed using a novel approach where a body force is applied orthogonally to the bulk freestream streamlines. Although the applied curvature is small, its effects on the development of the boundary layer are appreciable. The results indicate that spanwise curvature induces a non--uniform crossflow and alters the structure and alignment of turbulence, changing the distribution of turbulent stresses. These modifications are responsible for a misalignment between the Reynolds stress tensor and the velocity gradient tensor, affecting the validity of eddy-viscosity based turbulence models. Convex curvature, on the other hand, does not alter the distribution of the turbulent stresses, but reduces turbulent intensity. These results have important implications on the development of turbulence in general applications, such as the flow over a prolate spheroid, where streamline curvature is prominent. These results will be discussed in a streamline--aligned coordinate system.