International Research Fellow Awards Program: An Investigation of Secondary Vortex Structure in the Near Wake of a Circular Cylinder

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9600313 Borg The International Research Fellow Awards Program enables U.S. scientists and engineers to conduct three to twenty- four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad. This award will support a twelve-month postdoctoral research visit by Dr. John P. Borg to work with Dr. Mike Gaster at the University of Cambridge in the United Kingdom. This research will serve to extend non-obtrusive near wake control techniques over circular cylinders at or near critical Reynolds numbers (65Re1200). In so doing, this research will advance the fundamental understanding of transition, including location, causality and mechanisms. This research hopes to locate and identify the origin of a secondary vortex system, believed to be Tollmien-Schlichting waves, and the corresponding critical points, which are believed to form in the near wake and result in roll-up of the primary vortex. Pneumatic control ports in the shear layer and spanwise acoustic excitation are proposed to hinder the growth of the secondary system and extend critical Reynolds beyond current limits. In addition, a dynamical system is proposed to describe the interaction of both the primary and secodary vortex system. Such a system is to be used to develop an analytical model of transitional and turbulence. ***