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.

High lift/low drag wing and missile airframe

Abstract: An air launched, air-to-surface missile which has extended range and reduced radar cross section for low observability is disclosed. The design uses a triangular cross section fuselage, for low profile drag and reduced weight, a very high aspect ratio, such as 22.5, folding wing for low induced drag and three folding tail fins for less profile drag. The wing is a composite structure of graphite/epoxy sparcaps and 2024 aluminum alloy core with glass/epoxy skins and full depth Nomex.

The effect of chord-wise flexibility on the aerodynamic force generation of flapping wings: Experimental studies

Abstract: Wings of insects are flexible structures. Although there has been much recent progress in the area of insect flight aerodynamics, very little is known about how wing flexibility influences aerodynamic forces during flapping flight. We investigated this question using a dynamically scaled mechanical model of insect wings. Using a suite of wings with varying flexural stiffness (EI) values, we generated aerodynamic polar plots to characterize the force coefficients of flexible wings. These polar plots showed that the aerodynamic performance of the wings varied with wing flexibility. In general, aerodynamic force production decreased with increasing flexibility. Both lift and drag coefficients of wings are greater when wings are more rigid. However, at very high angles of attack, flexible wings generated greater lift than a rigid wing. In addition, the ratio of lift-to-drag also decreased with increasing flexibility. These data show that flexible wings offer no aerodynamic advantage over a rigid wing under steady state circumstances. Because wing material in insects is usually flexible but reinforced by wing veins, we tested the hypothesis that wing veins enhance the aerodynamic performance of wings by increasing their effective stiffness. Our data suggests that even a very basic framework of appropriately placed wing veins can substantially increase the functional rigidity of the wings thereby enhancing its aerodynamic performance.

Generalization of the Far-Field Drag Decomposition Method to Unsteady Flows

Abstract: Far-field drag-prediction and decomposition methods are powerful tools that increase the accuracy of the drag coefficient computed from computational fluid dynamics results by removing the spurious drag caused by numerical procedures. Furthermore, these methods allow a physical decomposition of the drag in terms of viscous, wave, and induced drag. However, they are currently limited to steady flows. This paper presents a generalization of the commonly used drag-prediction and decomposition method to unsteady flows. This generalized method, designed for three-dimensional viscous, subsonic, and transonic flows, is defined for both inertial and noninertial coordinate systems and allows drag decomposition to be performed on either static or moving/rotating meshes. This generalization also allows the drag caused by the unsteady fluctuations of the flow to be identified.

Reductions in induced drag by the use of aft swept wing tips

Abstract: Recent experimental and computational studies have indicated that rearward curvature of a wing can reduce the induced drag factor to values less than that obtained from the unswept elliptical wing considered optimal in classical wing theory. Wake non-planarity associated with a wing with aft swept tips has been suggested as a reason for this behaviour. This paper provides a systematic examination of the wake non-planarities induced by a variety of wing planforms and quantifies the induced drag reductions which may be expected. Results suggest a dependence of induced drag factor upon angle of attack, and therefore upon lift coefficient. The crescent wing is identified as the planform to derive the most benefit from its non-planar wake shape, typically a 4% reduction in induced drag factor at moderate angle of attack.

Aerodynamic drag control by pulsed jets on simplified car geometry

Abstract: Aerodynamic drag control by pulsed jets is tested in a wind tunnel around a simplified car geometry named Ahmed body with a rear slant angle of 35°. Pulsed jet actuators are located 5 × 10−3 m from the top of the rear window. These actuators are produced by a pressure difference ranging from 1.5 to 6.5 × 105 Pa. Their excitation frequency can vary between 10 and 550 Hz. The analysis of the control effects is based on wall visualizations, aerodynamic drag coefficient measurements, and the velocity fields obtained by 2D PIV measurements. The maximum drag reduction is 20 % and is obtained for the excitation frequency F j = 500 Hz and for the pressure difference ∆P = 1.5 × 105 Pa. This result is linked with a substantial reduction in the transverse development of the longitudinal vortex structures coming from the left and right lateral sides of the rear window, with a displacement of the vortex centers downstream and with a decrease in the transverse rotational absolute values of these structures.