You're invited to a seminar with Dr. Eric Matlis, an Associate Research Professor in the Aerospace and Mechanical Engineering Department at the University of Notre Dame, titled "Control of Stationary and Traveling Cross-flow Mode Interactions in High Speed Boundary Layers, or, Are Quiet Tunnels Always Required for Transition Research?"

Abstract: Recent experiments were performed at two Mach numbers to investigate the role of stationary and traveling cross-flow instability modes on boundary layer transition on a sharp right-circular yawed cone. The first experiment was conducted in the NASA Langley quiet Mach 3.5 Supersonic Low Disturbance Tunnel (SLDT), and the second in the US AirForce Academy Mach 6 conventional Ludwieg tunnel. Passive and active plasma discrete roughness elements were placed just upstream of Branch I of the linear stability neutral curve to excite both stationary and traveling cross-flow modes. Two roughness cases were considered; one at the most amplified wavenumber, and one at a subcritical wave number that was designed to inhibit the naturally growing stationary instability. Measurements consisting of off-wall streamwise and azimuthal mean and total pressure profiles verified the receptivity of the boundary layer to steady and unsteady excitation, while revealing quadratic interactions between stationary and traveling modes. Use of the subcritical forcing was found to delay transition by 40% in the NASA quiet tunnel but only 25% in the USAFA conventional tunnel, suggesting the possibility of either Mach number or environmental effects. Elucidating the role of non-linear secondary instability in transition and its sensitivity to background disturbances motivates the need for further research involving both quiet and conventional facilities. 

Biography: Dr. Eric Matlis is an Associate Research Professor in the Aerospace and Mechanical Engineering Department at the University of Notre Dame. Dr. Matlis's research interests include flow control, hydrodynamic stability, transition of high-speed boundary layers, novel uses of non-equilibrium plasmas, and aeroacoustics of rotorblade systems. Dr. Matlis is an associate fellow of the American Institute of Aeronautics and Astronautics (AIAA). Dr. Matlis has been awarded 5 patents. He received his Ph.D. (2004) at the University of Notre Dame, M.S. (1997) at the Illinois Institute of Technology, University and his B.S. (1994) from Northwestern University.