Boundary Layer Trips on Airfoils at Low Reynolds Numbers

Boundary Layer Trips on Airfoils at Low Reynolds Numbers -...

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AIAA 97-0511 Boundary Layer Trips on Airfoils at Low Reynolds Numbers C. Lyon, M. Selig, and A. Broeren University of Illinois at Urbana-Champaign Urbana, IL 35th Aerospace Sciences Meeting & Exhibit January 6-10, 1997 / Reno, NV For permission to copy or republish, contact the American Institute 01 Aeronautics and Astronautics 1801 Alexander Be" Drive, Suite 500, Reston, VA 22091
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BOUNDARY LAYER TRIPS ON AIRFOILS AT LOW REYNOLDS NUMBERS Christopher A. Lyon: ylichael S. Selig,! and Andy P. Broeren' Department of Aeronautical and Astronautical Engineering University of Illinois at Urbana-Cbampaign Urbana, Illinois 61801 Abstract Three categories of boundary layer trips (single 2-D plain. multiple 2-D plain. and 3-D trips) were tested on the M06-13-128. E374, and SD7037 airfoils over the Reynolds numbers of 100.000 to 300,000. Flow visual- ization and drag data were acquired for a number of trip heights and locations. To facilitate comparisons between airfoils. trips were located relative to untripped lami- nar separation locations. Drag data showed dramatic drag reductions for relatively thin trips, with thicker trips having slightly better performance. The trip lo- cation proved to be of little significance for trips located upstream of laminar separation. Little advantage was seen in utilizing multiple 2-D trips or complex 3-D trips over single 2-D trips. Finally, through the application of trips, it was not possible to improve the performance of an airfoil exhibiting large laminar separation bubbles over that of an untripped airfoil with small bubbles. I. Introduction At low Reynolds numbers. the presence of laminar separation bubbles often results in the increased drag seen on some airfoils. In an effort to mitigate these ad- verse effects and improve low Reynolds number airfoil performance, two principal approaches have been taken. First, by careful tailoring of the pressure distribution. bubble drag can be reduced through the introduction of early transition. A second well-known approach involves the use of mechanical turbulators (trip wires, plain trips, distributed grit roughness, zigzag tape, etc.) all of which tend to enhance the instability of the Tollmien- Schlichting waves that ultimately leading to turbulent flow. Any resulting benefit is believed to be attributable to the initiation of premature transition and the conse- quent reduction or elimination of the laminar separation bubble. Although effective tailoring of pressure distributions is well established. 1 ,2,3.4 transition enhancement by means of boundary layer trips is much less understood. The Copyright©1996 by Christopher A. Lyon. ~lichael S. Selig, and Andy P. Broeren. Published by the Ameri- can Institute of Aeronautics and Astronautics. Inc. with permission. ,. Graduate Research Assistant. Student ),Iember AIAA.
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