Lift-induced drag

About: Lift-induced drag is a research topic. Over the lifetime, 2861 publications have been published within this topic receiving 41094 citations.

Low Speed Design and Analysis of Wing/Winglet Combinations Including Viscous Effects

Abstract: The design and analysis of winglets is presented from an aerodynamic point of view. The winglets considered are small fences placed upward at the tip of the wing to improve the wing efficiency by decreasing the induced drag for a given lift. Viscous corrections are accounted for by using a two-dimensional viscous polar, with the assumption that at design conditions the flow is fully attached. The comparison of the inviscid and viscous designs indicates that viscosity has little effect on the optimum geometry. In the presence of viscous drag, the winglets produce a small thrust; due to viscosity, the overall efficiency gain is decreased. The effect of a small yaw angle on a wing equipped with such optimal winglets indicates that, even in the presence of viscous effects, they provide weathercock stability.

Unsteady turbulent boundary layers in swimming rainbow trout.

Abstract: The boundary layers of rainbow trout, Oncorhynchus myskiss , swimming at 1.02±0.09 L s−1 (mean±s.d., N =4), were measured by the Particle Image Velocimetry (PIV) technique at a Reynolds number of 4×105. The boundary-layer profile showed unsteadiness, oscillating above and beneath the classical logarithmic law of the wall with body motion. Across the entire surface regions that were measured, local Reynolds numbers based on momentum thickness, which is the distance that is perpendicular to the fish surface through which the boundary-layer momentum flows at free-stream velocity, were greater than the critical value of 320 for laminar-to-turbulent transition. The skin friction was dampened on the convex surface while the surface was moving towards a free-stream flow and increased on the concave surface while retreating. These observations contradict the result of a previous study using different species swimming by different methods. Boundary layer compression accompanied by an increase in local skin-friction was not observed. Thus, the overall results may not support absolutely the Bone-Lighthill boundary-layer thinning hypothesis that the undulatory motions of swimming fish cause a large increase in their friction drag because of the compression of the boundary layer. In some cases, marginal flow separation occurred on the convex surface in the relatively anterior surface region, but the separated flow reattached to the fish surface immediately downstream. Therefore, we believe that a severe impact due to induced drag components (i.e. pressure drag) on the swimming performance, an inevitable consequence of flow separation, was avoided.

Two-Dimensional Subsonic Wind Tunnel Evaluation of a 20-Percent-Thick Circulation Control Airfoil

Abstract: : A circulation control uncambered elliptic airfoil section with a thickness-to-chord ratio of 0.20 was tested subsonically to determine its aerodynamic characteristics. Lift coefficients up to 5 were produced at momentum coefficients, of 0.24. The initially high unblown drag coefficients, characteristic of bluff trailing edge airfoils, were greatly reduced at low values of momentum coefficient. It was therefore possible to produce equivalent lift-to-drag ratios in excess of 30 when Cl = 1.0. The ability to produce high lift coefficients essentially independent of angle of attack is indicated by the results of this investigation.

Supercirculation effects induced by vectoring a partial-span rectangular jet

Abstract: Thrust-induced supercirculation effects from thrust vectoring have indicated a potential for not only increasing maneuverability of fighter aircraft but also as a means of improving cruise performance. The current study investigated a partial-span rectangular jet-exhaust nozzle located at the wing trailing edge that acts similar to a jet flap by increasing lift due to supercirculation. This paper summarizes experimental studies including the effects of nozzle deflection angle, wing camber, and nozzle shape and exit location on lift, drag and load distributions. The results indicate that significant increases in thrust-induced lift along with substantial decreases in drag are possible.