STABILITY OF THREE-DIMENSIONAL BOUNDARY LAYERS:
EXPERIMENTS AND COMPUTATIONS
Helen L. Reed
Professor and Head
Texas A&M University
The stability and transition of three-dimensional boundary layers is important for many applications (e.g. swept wings). In these flows, nonlinear distortions of the basic flow may occur early on due to the primary crossflow instability. These flows are characterized by an extensive distance of nonlinear evolution with eventual saturation of the fundamental disturbance, leading to the strong amplification of very-high-frequency inflectional instabilities and breakdown. Recent advances in modeling, simulation, and experiments are discussed, as well as our new understanding of the basic physics related to receptivity to freestream sound and vorticity and surface roughness. It is demonstrated that advances in our prediction and identification of basic mechanisms come from those groups performing complementary computations and experiments. In particular, our team studied incompressible swept-wing flows, efficiently sorted out the effects of curvature and nonlinearities, and elucidated a promising approach to transition delay in these flows. It was determined that discrete roughness applied near the attachment line can control crossflow and maintain a laminar boundary layer, provided an induced roughness wavelength is below a critical value.