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.

Wind-Tunnel Investigations of Wings with Serrated Sharp Trailing Edges

Abstract: Exploratory wind-tunnel force measurements are presented for two wing geometries with small-scale planar and nonplanar serrated trailing-edge devices (chord-Reynolds numbers ranged from 1.0–3.7 × 106). The planar serrated trailing-edge extensions reduced the drag at conditions when trailing-edge separation occurred at low angles of attack. The introduction of serrations reduced or eliminated the drag penalty due to the small (1–2 percent of the chord length) nonplanar trailing-edge flaps, while maintaining the effects of increase in camber. The presence of streamwise vortices immediately downstream of the serrated trailing edges is believed to have favorably affected the boundary-layer flow approaching the trailing edge and the near-wake development, resulting in reduced pressure (form) drag.

Span Morphing: A Conceptual Design Study

Abstract: The use of variable wing span to enhance flight performance and control authority of high endurance, medium altitude UAV is investigated. Asymmetric span extension is used to replace ailerons and maintain roll control over the entire flight envelope of the vehicle. The span extension required to generate a rolling moment equal to that produced by ailerons is estimated at four flight points. The study is performed using Tornado Vortex Lattice Method (VLM). 36% increase in wing semi-span is required to maintain roll authority. On the other hand, symmetric span morphing is used to reduce induced drag and enhance the endurance capability of the vehicle. 20% symmetric span morphing was found to be the optimum to reduce the overall drag of the wing by 10% at the start of cruise and 2.5% at the end of cruise. The morphing wing structure is to be designed using Zero Poisson’s ratio Accordion honeycomb with elastomeric skins. The geometry of the honeycomb will be optimised using the Genetic Algorithm (GA) optimiser to minimise the structural weight of the wing while meeting various design constraints.

Vortex-induced drag and the role of aspect ratio in undulatory swimmers

Abstract: During cruising, the thrust produced by a self-propelled swimmer is balanced by a global drag force. For a given object shape, this drag can involve skin friction or form drag, both being well-documented mechanisms. However, for swimmers whose shape is changing in time, the question of drag is not yet clearly established. We address this problem by investigating experimentally the swimming dynamics of undulating thin flexible foils. Measurements of the propulsive performance together with full recording of the elastic wave kinematics are used to discuss the general problem of drag in undulatory swimming. We show that a major part of the total drag comes from the trailing longitudinal vortices that roll-up on the lateral edges of the foils. This result gives a comparative advantage to swimming foils of larger span thus bringing new insight to the role of aspect ratio for undulatory swimmers.

Aerodynamics of spherical balloon wind sensors

Abstract: A preliminary analysis of the response characteristics of spherical balloon wind sensors is presented. It is shown that smooth superpressure spheres do not provide accurate detailed wind profiles and that the response characteristics can be improved by the addition of roughness elements. Experimental data show that surface roughness elements on a spherical balloon stabilize the drag force vector and reduce the lift force. Spurious aerodynamically induced motions are significantly reduced, and the balloon more accurately senses the true wind.