Role of Micron - Sized Roughness in Swept - Wing Transition

Paper #:
  • 921986

Published:
  • 1992-10-01
Citation:
Radeztsky, R., Reibert, M., Saric, W., and Takagi, S., "Role of Micron - Sized Roughness in Swept - Wing Transition," SAE Technical Paper 921986, 1992, https://doi.org/10.4271/921986.
Pages:
9
Abstract:
Stability and transition experiments are conducted in the Arizona State University Unsteady Wind Tunnel on a 45° swept airfoil. The pressure gradient is designed so that transition and stability are purely crossflow-dominated. Flow visualization and hot-wire measurements show that the development of the crossflow vortices is influenced by roughness near (not at) the attachment-line. Comparisons of transition location are made between a painted surface (distributed 9 μm peaks and valleys on the surface), a machine-polished surface (0.5 μm rms finish), and a hand-polished surface (0.25 μm rms finish). Then, isolated 6 - 9 μm roughness elements are placed near the attachment line on the airfoil surface under conditions of the final polish (0.25 μm rms). These elements amplify a centered stationary crossflow vortex and its neighbors, resulting in localized early transition. The diameter and height of these roughness elements are varied in a systematic manner. Spanwise hot-wire measurements are taken behind the roughness element to document the enhanced vortices. These scans are made at several different chord locations to examine vortex growth.
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