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4.22.15 Saric


Prof. William S. Saric, Aerospace Engineering, Texas A&M University
April 22, 2015, 10:00 am, NIA, Room 101

Micron-sized, spanwise periodic, discrete roughness elements (DREs) were applied to and tested on a 30° swept wing model in order to study their effects on boundary layer transition in flight where stationary crossflow waves are the dominant instability. Significant improvements have been made to previous flight experiments in order to more reliably determine and control the model angle of attack (α) and unit Reynolds number (Re′). These improvements will aid in determining the influence that DREs have on swept wing, laminar turbulent transition. Two interchangeable leading edge surface roughness configurations were tested: highly polished and painted. The baseline transition location for the painted leading edge (increased surface roughness) was unexpectedly farther aft than the polished. Transport unit Reynolds numbers were achieved using a Cessna O 2A Skymaster. Infrared thermography, coupled with a post-processing code, was used to globally extract a quantitative boundary layer transition location. Each DRE configuration was compared to curve fitted baseline data in order to determine increases or decreases in percent laminar flow while accounting for the influence of small differences in Re’ and α. Linear Stability Theory (LST) guided the DRE configuration test matrix. In total, 63 flights were completed, where only 30 of those flights resulted in useable data. While the results of this research have not reliably confirmed the use of DREs as a viable laminar flow control technique in the flight environment, it has become clear that significant computational studies, specifically direct numerical simulation (DNS) of these particular DRE configurations on this model geometry and flight conditions, are a necessity in order to better understand the influence that DREs have on laminar-turbulent transition.

William S. Saric is a University Distinguished Professor and holds the George Eppright ’26 Chair in Engineering at Texas A&M University where he has been since Jan 2005. He received his PhD in Mechanics from the Illinois Institute of Technology in 1968 and has held appointments at Sandia National Laboratories (Re-entry Vehicles 1963-66; Atomic & Fluid Physics, 1968-75), Virginia Tech (Engineering Science & Mechanics, 1975-84), and Arizona State University (Mechanical & Aerospace Engineering, 1984-2005). He is a member of the National Academy of Engineering and The Academy of Medicine, Engineering, and Science of Texas. He received the AIAA Fluid Dynamics Award (2003), the SES G.I. Taylor Medal (1993), the AGARD (NATO) Scientific Achievement Award (1996). He is a Fellow of AIAA, APS, and ASME and was Chair of the AIAA Transition Study Group (2000-2012). He has re-established two major wind tunnels and a flight research laboratory at Texas A&M University and was the Director of the AFOSR/NASA National Center for Hypersonic Laminar-Turbulent Transition Research. Most recently, he has conducted computational, experimental, and flight research on stability, transition, and control of 2-D and 3-D boundary layers over a range of Mach numbers.



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