Skip to main content
No Access

Flight experiments on the effects of step excrescences on swept-wing transition

Published Online:pp 171-180

A 30° swept-wing model with a movable, leading-edge extending to 15% chord is used in flight tests to study the effect of two-dimensional, step excrescences on swept-wing transition, where stationary-crossflow waves are typically the dominant instability. Transport unit Reynolds numbers are achieved using a Cessna O-2A Skymaster. Forward- and aft-facing steps are modulated in-flight. Pressure measurements are compared with CFD. Infrared thermography is used to globally detect boundary-layer transition. When the 2-D pressure gradient matches the unswept case, the swept-wing case has a lower Rekk,crit. However, there is still potential to relax conventional, laminar-flow tolerances for steps.


2-D roughness, step excrescences, forward-facing step, backward-facing step, boundary-layer transition, laminar flow, transport Reynolds number, flight research, crossflow instability, swept wings


  • 1. Arnal, D. , Archambaud, J.P. (2009). ‘Laminar-turbulent transition control: NLF, LFC, HLFC’. Advances in Laminar-Turbulent Transition Modeling. VKI Lecture Series. Brussels, Belgium:Von Karman Institute for Fluid Dynamics , ISBN: 978-92-837-0090-6 Google Scholar
  • 2. Bender, A.M. , Drake, A. , McKay, V.S. , Westphal, R.V. , Yoshioka, S. , Kohama, Y. (2007). ‘An approach to measuring the effects of surface steps on transition using a propelled model’. ICIASF ‘07 Record Google Scholar
  • 3. Bender, A.M. , Harris, C. , Westphal, R. (2013). ‘The effects of favorable pressure gradient on boundary layer transition with 2D excrescences’. Presentation at 3AF Conference, St. Louis, France Google Scholar
  • 4. Carpenter, A.L. , Saric, W.S. , Reed, H.L. (2010). ‘Roughness receptivity in swept-wing boundary layers – experiments’. Int’l. J. Eng. Sys. Modeling and Simulation. 2, 1, 128-138 AbstractGoogle Scholar
  • 5. Crawford, B.K. , Duncan, G.T., Jr. , West, D.E. , Saric, W.S. (2013). ‘Laminar-turbulent boundary layer transition imaging using IR thermography’. Optics and Photonics Journal. 3, 3, 233-239, 10.4236/opj.2013.33038 Google Scholar
  • 6. Drake, A. , Bender, A.M. (2009). Surface Excrescence Transition Study. AFRL-RB-WP-TR-2009-3109 Google Scholar
  • 7. Drake, A. , Bender, A.M. , Westphal, R.V. (2008). Transition due to Surface Steps in the Presence of Favorable Pressure Gradients. AIAA Paper No. 2008-7334 Google Scholar
  • 8. Drake, A. , Westphal, R.V. , Zuniga, F.A. , Kennelly, R.A. , Koga, D.J. (1996). Wing Leading Edge Joint Laminar Flow Tests. NASA TM 4762 Google Scholar
  • 9. Fanning, J.A. (2012). In-Flight Measurements of Freestream Atmospheric Turbulence Intensities. Texas A&M University, Master’s thesis Google Scholar
  • 10. Reed, H.L. , Saric, W.S. (1989). ‘Stability of three-dimensional boundary layers’. Ann. Rev. Fluid Mech.. 21, 1, 235-284 Google Scholar
  • 11. Saric, W.S. (1994). ‘Görtler vortices’. Ann. Rev. Fluid Mech.. 26, 1, 379-409 Google Scholar
  • 12. Saric, W.S. , Reed, H.L. , White, E.B. (2003). ‘Stability and transition of three-dimensional boundary layers’. Ann. Rev. Fluid Mech.. 35, 1, 413-440 Google Scholar
  • 13. Tucker, A.A. , West, D.E. , Crawford, B.K. , Saric, W.S. (2013). Flexible Flight Research Platform at Texas A&M University Flight Research Laboratory. AIAA-2013-2927 Google Scholar
  • 14. Tufts, M.E. , Duncan, G.T., Jr. , Crawford, B.K. , Reed, H.L. , Saric, W.S. (2014). ‘Computational design of a test article to investigate 2-D surface excrescences on a swept laminar-flow wing’. Int. J. Engineering Systems Modelling and Simulation. 6, 3/4, 181-190 AbstractGoogle Scholar