![]() This makes the boundary layer much more stable with respect to the growth of small disturbances (e.g., Tollmien-Schlichting waves). (Recall from Chapter 3 that for a fixed pressure gradient a critical Reynolds number based on boundary-layer thickness must be reached before transition is possible.) Second, it creates a much fuller velocity profile within the boundary layer, somewhat similar to the effect of a favorable pressure gradient. First, it reduces the boundary-layer thickness. Valentine, in Aerodynamics for Engineering Students (Seventh Edition), 2017 10.5.1 Laminar Flow Control by Boundary-Layer Suctionĭistributed suction acts in two main ways to suppress laminar-turbulent transition. The research showed that at the test condition of Mach 2 at 53000 ft ( R e of the order of 22.7 × 10 6) the laminar boundary layer was sustained as far aft as 46% of the chord.įinally, van de Wal showed merely 3.2% reduction in total drag of a small GA aircraft (ENAER Namcu), reporting that installing a boundary layer suction system was not beneficial to its operation.Į.L. In 1999, Marshall investigated the effectiveness of a variable-porosity suction glove on the F-16XL-2 aircraft to demonstrate the feasibility of boundary layer suction for supersonic operation. The system, while demonstrating LFC was effective, turned out to be a manufacturing and maintenance nightmare and too costly to be practical. The bleed air from these engines was then used to drive a compressor that, effectively, sucked the wing boundary layer through slots in the wing. Its two original Allison J71 engines, originally on the wing, were replaced with two GE XJ79s that were mounted to the rear fuselage. (Photos by Phil Rademacher)Īn early example involves the Northrop X-21A, which was a heavily modified Douglas WB-66D aircraft. Furthermore, it is a serious detriment that the perforations negatively affect the structural integrity of the wing and the operator must deal with nuisances such as cleaning the remains of insects that can clog the perforations, reducing system performance.įIGURE 15-24. In other words, additional energy is required to lower the pressure inside the wing and draw in the external boundary layer. The primary drawback of such methods is that they are active rather than passive. A variation of LFC, called hybrid LFC or HLFC, uses NLF for a larger portion of the wing to reduce the power required to eliminate the turbulent boundary layer growth. LFC is an attempt to maintain the laminar boundary layer over a large part of the wing by effectively “sucking” the turbulent boundary layer through tiny perforations in the wing skin. LFC is also referred to as artificial laminar flow (ALF) to contrast with natural laminar flow (NLF). The history of LFC dates back to 1930s and is well documented by Chambers and in particular Braslow. ![]() Snorri Gudmundsson BScAE, MScAE, FAA DER(ret.), in General Aviation Aircraft Design, 2014 Reduction of Drag on Wings via Laminar Flow Control (LFC)
0 Comments
Leave a Reply. |