A New Method of Determining Roughness Height For Low-Reynolds-Number Flows
Open Access
- Author:
- Morgan, Nicholas
- Area of Honors:
- Aerospace Engineering
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Mark David Maughmer, Thesis Supervisor
Robert Graham Melton, Thesis Honors Advisor
Amy Ruth Pritchett, Faculty Reader - Keywords:
- airfoil
fixed transition
forced transition
low Reynolds
S407
E387
transition
Braslow
LSLT Wind Tunnel
Wind Tunnel
Low-Speed - Abstract:
- Prior investigations of forced transition on airfoils by Braslow and Knox have shown that fully developed turbulent flow can be achieved over an aerodynamic surface without significant increases in drag beyond that of the turbulent flow over the surface of the airfoil. It was thought that the roughness height needed to accomplish this, the critical roughness height, could not force transition at low Reynolds numbers. Experimental data measured at the Pennsylvania State University Low-Speed, Low-Turbulence (LSLT) Wind Tunnel proved that forced transition could occur with greater-than-critical roughness heights and without significantly increasing drag at low Reynolds numbers. Examples of this can be found in drag polar plots for the S407 and E387 airfoils with fixed transition. Analysis of this data was completed to understand the behavior and compare it to the established Braslow and Knox method. This report also offers method of determining the roughness height needed to fix transition for low Reynolds numbers based upon experimental results by relating the ratio of roughness height over roughness station to the Reynolds number at the roughness station.