Design and Testing of a 30-Degree Sweep Laminar Flow Wing for a High-Altitude Long-Endurance Aircraft
NORTHROP GRUMMAN CORP EL SEGUNDO CA INTEGRATED SYSTEMS
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A laminar flow wing was designed for a high-altitude long-endurance flying-wing aircraft with a sweep angle of 30 degrees. The resulting wing design satisfied the lift and pitching moment requirements of the aircraft and had extensive runs of laminar flow on the upper and lower surface. A portion of the wing was tested in a low-speed wind tunnel at flight Reynolds number with an equivalent pressure distribution designed to reproduce the effects of the transonic cruise Mach number. Measurements of the boundary layer included transition location, local shear stress, and limited boundary layer profiles. To examine the boundary layer characteristics of the wing design, a section of the wing was modelled in a 7-ft x 10-ft low-speed wind tunnel. The model scale was selected to match Reynolds number to the flight conditions. Extensive computational design effort was spent modifying the wing and developing wall treatments to ensure that the low-speed wind tunnel model pressure distribution matched that of the transonic free-air flight condition. The resulting wall treatments were substantially less extensive than is conventionally assumed to be necessary. Measurement of the pressure distributions on the model confirmed that the wall treatments successfully compensated for the presence of the walls. The experimental results correlated well with pre-test stability calculations. Extensive runs of laminar flow were observed with the 30-degree leading edge wing sweep. Multiple measurement methods showed that with the careful attention to boundary layer stability paid during design of the wing, for a typical cruise condition for a high altitude long-endurance aircraft, extensive laminar flow with minimal separation can be achieved, leading to substantial drag reduction.
- Fluid Mechanics