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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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Journal ArticleDOI
A E Vardy1
01 Jan 1996
TL;DR: In this article, it is shown that aerodynamic drag on trains in tunnels includes friction drag and pressure drag, which are respectively the algebraic sums of the longitudinal components of all shear and normal forces on the train surfaces.
Abstract: Aerodynamic drag on trains in tunnels includes friction drag and pressure drag, which are respectively the algebraic sums of the longitudinal components of all shear and normal forces on the train surfaces. The first of these is broadly similar to its counterpart in the open. The second is shown to include two effects that are usually negligible in the open.It is shown that the overall drag force must be regarded as the sum of individual components, each of which behaves differently from the others. The components can be represented by non-dimensional coefficients whose numerical values are nearly constant for a wide range of train journeys. In contrast, the overall drag coefficient is shown to vary significantly, even during any particular journey.The principal causes of aerodynamic drag in tunnels are also the principal causes of pressure waves that give rise to potential aural discomfort for passengers. It is argued that a common method of analysis is appropriate for the prediction of both of these eff...

29 citations

Journal ArticleDOI
TL;DR: In this article, the aerodynamic performance of two high aspect-ratio wings flying in formation is investigated with particular interest in the importance of considering wake rollup in making aerodynamic predictions.
Abstract: The aerodynamic performance of two high aspect-ratio wings flying in formation is investigated with particular interest in the importance of considering wake rollup in making aerodynamic predictions. For this purpose, formations of various separations were investigated using a drag-free, fixed-wake model as well as a force-free, relaxed one. In all cases the aircraft were trimmed for roll and the follower aircraft pitch attitude was adjusted to match the lift coefficient of the lead aircraft. Both wake representations result in similar induced-drag minima for the follower aircraft which result when the lateral overlaps of the two aircraft are around 10% of a wingspan. Computations with the fixed-wake model, however, predict a wider region of lateral separations having the lowest induced drag than do the simulations with wake rollup. A small performance difference due to the wake model also exists when one aircraft follows directly behind the other. Independent of the wake model used, trimming the aircraft in roll and pitch can have a significant influence on their performance, although the required control-input solutions for trim are essentially not affected by the choice of wake representation.

29 citations

Journal ArticleDOI
TL;DR: Wake surveys of two swept NACA 0021 wings were conducted at angles of attack of 0°, 3°, 6°, 9°, 12°, and 12° as mentioned in this paper.

29 citations

Proceedings ArticleDOI
09 Jan 2006
TL;DR: In this paper, the authors present a three-dimensional airframe design methodology for low noise emission and high fuel efficiency, based on a blended-wing-body type aircraft, using a combination of high and low fidelity tools to assess the performance and acoustics of the aircraft.
Abstract: This paper presents a three-dimensional airframe design methodology for low noise emission and high fuel efficiency, based on a blended-wing-body type aircraft. The design methodology uses a combination of high and low fidelity tools to assess the performance and acoustics of the aircraft. The goal set by the Silent ** Aircraft Initiative is a viable, commercial aircraft design with noise levels imperceptible outside the airport perimeter in a well-populated urban environment. To be viable, the aircraft requires a fuel burn comparable to modern conventional aircraft. The detailed airframe design incorporates leading edge camber of the centerbody to provide pitch trim without penalties in induced drag, wave drag, and trim drag. A low noise approach is achieved with reduced approach velocity and increased distance between the airframe and the observer. This slow and steep approach profile is enabled through a combination of thrust vectoring, quiet drag generation, and leading edge high-lift devices. The blended-wing-body type airframe design presented in this paper is both quiet with an OASPL of approximately 65 dBA and highly efficient with a cruise ML/D of 18.5. The paper concludes with ideas to further reduce noise to meet the aggressive SAI goal with minimal cruise performance penalty.

29 citations

Journal ArticleDOI
TL;DR: In this paper, the minimum energy loss occurs when the vortex wake moves as a rigid surface that rotates about the wing root, a condition analogous to that determined for a slow-turning propeller.
Abstract: For slow flapping motions it is found that the minimum energy loss occurs when the vortex wake moves as a rigid surface that rotates about the wing root - a condition analogous to that determined for a slow-turning propeller. The optimum circulation distribution determined by this condition differs from the elliptic distribution, showing a greater concentration of lift toward the tips. It appears that very high propulsive efficiencies are obtained by flapping.

29 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202344
2022105
202138
202046
201944
201849