Topic
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.
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TL;DR: In this paper, the authors studied the dynamics of lift and thrust generation by flying animals by considering the distribution of vorticity in the wake of flying animals, and derived the induced power as the rate of increase of wake kinetic energy.
Abstract: The mechanics of lift and thrust generation by flying animals are studied by considering the distribution of vorticity in the wake As wake generation is not continuous, the momentum jet theory, which has previously been used, is not satisfactory, and the vortex theory is a more realistic model The vorticity shed by the wings in the course of each powered stroke deforms into a small-cored vortex ring; the wake is a chain of such rings The momentum of each ring sustains and propels the animal; induced power is calculated as the rate of increase of wake kinetic energy A further advantage of the vortex theory is that lift and induced drag coefficients are not required; estimated instantaneous values of these coefficients are generally too large for steady state aerodynamic theory to be appropriate to natural flapping flight The vortex theory is applied to hovering of insects and to avian forward flight A simple expression for induced power in hovering is found Induced power is always greater than simple momentum jet estimates, and the discrepancy becomes substantial as body mass increases In hovering the wake is composed of a stack of horizontal, coaxial, circular vortex rings In forward flight of birds the rings are elliptic; they are neither horizontal nor coaxial because the momentum of each ring balances the vector sum of parasite and profile drag and the bird9s weight Total power consumption as a function of flight velocity is calculated and compared for several species Power reduction is one of the major factors influencing the choice of flight style A large body of data is used to obtain an approximate scaling between stroke period and the body mass for birds Together with relations between other morphological parameters, this is used to estimate the variation of flight speed and power with body mass for birds, and on this basis deviations from allometric scaling can be related to flight proficiency and to the use of such strategies as the bounding flight of small passerines Note: Present address: Department of Zoology, University of Bristol, Woodland Road, Bristol BS8 IUG, UK
332 citations
01 Jan 1984
TL;DR: In this article, the effect of rib details on the riblet drag reduction performance was investigated in boundary layers having different upstream histories and at higher Reynolds numbers than previously reported, and it was found that the drag reduction was dependent on the height and spacing of riblets in law of the wall variables regardless of the free-stream Reynolds number or upstream boundary-layer history.
Abstract: Riblet surfaces have been tested in boundary layers having different upstream histories and at higher Reynolds numbers than previously reported. The drag reduction for the riblet surfaces was found to be dependent on the height and spacing of the riblets in law-of-the-wall variables regardless of the free-stream Reynolds number or upstream boundary-layer history. Micro-photographs of the actual riblet geometries are examined to determine the effect of rib details on the riblet drag-reduction performances. To further increase drag-reduction performance, riblet surfaces are combined with another drag-reduction concept, the large-eddy breakup device (LEBU). In addition, the yaw sensitivity of riblets is evaluated, as well as the characteristics of riblet surfaces manufactured out of a thin vinyl sheet.
289 citations
TL;DR: In this article, a review of recent studies on the drag-reducing shapes, structures, and behaviors of swimming and flying animals are reviewed, with an emphasis on potential analogs in vehicle design.
Abstract: Recent studies on the drag-reducing shapes, structures, and behaviors of swimming and flying animals are reviewed, with an emphasis on potential analogs in vehicle design. Consideration is given to form drag reduction (turbulent flow, vortex generation, mass transfer, and adaptations for body-intersection regions), skin-friction drag reduction (polymers, surfactants, and bubbles as surface 'additives'), reduction of the drag due to lift, drag-reduction studies on porpoises, and drag-reducing animal behavior (e.g., leaping out of the water by porpoises). The need for further research is stressed.
286 citations
TL;DR: In this paper, the authors describe an approach for measuring directly fluctuating lift and drag forces and steady mean drag forces on a cylinder placed so that its central axis is perpendicular to the direction of flow of water in a channel.
Abstract: Apparatus is described for measuring directly fluctuating lift and drag forces and steady mean drag force. These forces are exerted upon a cylinder placed so that its central axis is perpendicular to the direction of flow of water in a channel. Results are given for the stationary cylinder for the range of Reynolds number 3600 to 11 000.
277 citations
TL;DR: In this paper, the performance of 3 M riblets on airfoils, wings and wing-body or aircraft configurations at different speed regimes are reviewed; these applications bring in additional effects like pressure gradients and three dimensionality.
275 citations