Abstract
Streamwise counter-rotating vortices and the associated streaks evolve in incompressible or compressible
boundary layer flows and are excited by various disturbances from the freestream or as a result of wall
surface nonuniformities. Following the transient growth phase, these fully-developed vortex structures
become susceptible to inviscid secondary instabilities that may trigger early transition to turbulence via
bursting processes. Görtler vortices, in particular, develop in boundary layer flows along concave surfaces
as a result of the imbalance between radial pressure gradient and centrifugal effects. From the practical
standpoint, boundary layer flows over concave walls occur in a number of technological applications
ranging from subsonic to hypersonic regime, such as flows past turbine blades and supercritical airfoils
designed for laminar flow control or flows along the walls of high-speed wind tunnels as well as along the
forebody compression surface ahead of a scramjet engine. In this talk, our previous and current efforts to
analyze and control Görtler vortices in both subsonic and supersonic boundary layers are discussed. The
primary mathematical model is the set of nonlinear boundary region equations, which represent the high
Reynolds number asymptotic extension of the Navier-Stokes equations, under the assumption that the
streamwise wavenumber of the disturbances is much smaller than the crossflow wavenumbers. A
nonlinear optimal control strategy based on Lagrange multipliers, that can be applied to both
incompressible and compressible boundary region equations, is introduced and described. The objective
functional is represented by the wall shear stress or the kinetic energy of vortices, while the control
variable is either wall deformation, transpiration or heating. Results for a wide range of Mach numbers
indicate that the control strategy proves to be successful in diminishing both the wall shear stress and the
energy of vortices.
Bio
Adrian Sescu is currently an Associate Professor and Director of Undergraduate Studies in the
Department of Aerospace Engineering, Mississippi State University. He is also affiliated with the High-
Performance Computing Collaboratory (HPCC), a coalition of MSU member institutes and centers aimed
at advancing the state-of-the-art in computational science and engineering. He has been a postdoctoral
associate in the Turbulence Research Group of the Department of Mechanical Engineering, Johns
Hopkins University, and multiple times affiliated with Air Force Research Lab. He received his PhD
degree in Mechanical Engineering from the University of Toledo, under a collaboration with NASA
Glenn Research Center, and his MS and BS degrees in Aerospace Engineering from the Polytechnic
University of Bucharest. His research interests cover topics in boundary layer transition and control,
aeroacoustics, and turbulence in fluids. He is an Associate Fellow of the American Institute of
Aeronautics and Astronautics, and active in various committees under the American Physical Society,
Division of Fluid Dynamics.
Host: Professor Leo Chamorro
