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Numerical Study of Wingtip Shed Vorticity Reduction by Wing Boundary Layer Control Jose Alejandro Posada Wingtip vortex reductions have been obtained by Boundary Layer Control application to an AR=1.5 rectangular wing using a NACA 0012 airfoil. If wingtip shed vorticity could be reduced significantly, then so would induced drag resulting in improved cruise fuel economy. Power savings would be even more impressive at low flight speed or in climb. A two dimensional wing produces lift without wingtip vorticity. Its bound vorticity, Γ, equals the contour integral of the boundary layer vorticity γ or ∫ ⋅ = Γ dl γ . Where the upper and lower boundary layers meet at the cusped TE, their local static pressure pu=pl then the boundary layer outer edge inviscid velocity Vupper=Vlower and γlower=-γupper. This explains the 2-D wing self cancellation of the upper and lower surface boundary layer vorticity when they meet upon shedding at the trailing edge. In finite wings, the presence of spanwise pressure gradients near the wing tips misaligns γlower and γupper at the wingtip TE preventing the upper and lower surface boundary layers from completely canceling each other. To prevent them from generating wing tip vortices, the local boundary layers need to be captured in suction slots. Once vorticity is captured, it can be eliminated by viscous mixing prior to venting over board. The objective of this dissertation was to use a commercial Computational Fluid Dynamics code (Fluent) to search for the best configuration to locate BLC suction slots to capture non-parallel boundary layer vorticity prior to shedding near the wingtips. The configuration selected for running the simulations was tested by trying to duplicate a 3D wing for which sufficient experimental and computational models by others are available. The practical case selected was done by Chow et al in the 32 x 48 in. low speed wind tunnel at the Fluid Mechanics Laboratory of NASA Ames Research Center, and computationally analyzed by Dacles-Mariani et al, and Khim and Rhee. The present computed pressure coefficient values compare very well (Figure 90). The present simulations were also validated by comparison with wake survey and balance type experimental measurements done by Chometon and Laurent on a NACA 643-018 wing. Lift, induced drag, and profile drag coefficients agree very well with Chometon and Laurent data. More than one hundred simulations were performed with different BLC suction slot geometries. Suction slots were used in the chord-wise and span-wise locations near the wing tip region. Blowing slots were evaluated at the wing center line, the wing tip upper surface, and span-wise outside of the wing tip. For an elliptically loaded wing, 50% of the bound vorticity is shed at the wing tips over a length of 7% of the wing span. The turbulent boundary layer thickness for a Cessna 206 aircraft at cruise is estimated as 0.09 ft. Theoretically the power required to remove by suction all the upper and lower surface boundary layer over the tip region for this aircraft at take-off is 2.6 HP, which would be very small compared to the 70 HP induced drag power saved. This would only be true if 100% wingtip vortex elimination could be obtained.

Numerical study of wingtip shed vorticity reduction by wing Boundary Layer Control