![]() The Air Force Research Laboratory issued a grant to Saric and Reed for an experiment that flew to Mach 0.3, a lift coefficient of 0, and a Reynolds number of about 7 million, and showed laminar flow back to about 70 percent over a 30-degree swept wing.įay Collier, NASA’s expert in laminar flow, was so interested in their idea that he wanted to pursue it further. By carefully adapting the size of the bumps to the depth of the boundary layer (that part of the air flowing next to the skin of the wing), a stable wave can be established in the boundary layer and this allows the flow to remain laminar for long runs (30 to 50 percent of the upper surface) over the wing. Saric and Reed’s simple but brilliant idea was to put bumps on the laminar-flow part of a test wing. Let me say that again: if waves are excited to a higher frequency, airflow is stable that is, it remains laminar and does not immediately break down and transition to turbulent flow. It’s a known fact that if airflow is excited to a HIGHER frequency than the unstable frequency, waves are stable. The idea Saric and Reed had is so good it’s simply sheer genius. Today, a new program is getting under way at NASA Dryden that will use the center’s Gulfstream III aircraft and build on the work of the world’s most knowledgeable researchers in this area, Bill Saric and Helen Reed of Texas A&M University. Research by the NACA began in the 1930s with smoke trails photographed in a Langley wind tunnel and continued through the 1990s using such test beds as a Lockheed JetStar and an F-16XL. In various efforts dating back decades, NASA has attempted to achieve that ideal. The ideal would be laminar airflow across the entire surface of the wing with no sign of turbulence, which hinders flying performance by increasing aerodynamic drag and fuel consumption. As air moves across a wing, it’s altered by the friction between it and the wing’s surface, changing from a laminar, or smooth, flow at the forward area to more turbulent flow toward the trailing edge. A certain amount of air turbulence occurs on the surface of most aircraft wings, regardless of their shape and size. Laminar flow is essentially the way airflow travels above and below wing surfaces. The tiny vertical airfoils mounted outboard of the black test section are vortex generators that keep the airflow attached over the wing surface at cruising speed. Image: The black test section of the upper wing skin on this NASA Gulfstream III research aircraft has a line of miniscule bumps at the leading edge that allows the boundary layer airflow to remain stable and smooth over most of the wing’s upper surface. NASA (and the NACA before us) has spent a LOT of effort and money to make laminar flow work in real-world applications, which would mean dramatic improvements in fuel efficiency. For aerospace engineers, the holy grail of low drag means conquering laminar flow.
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