Continuous research efforts have been devoted to the fundamental understanding of aircraft aerodynamics and the introduction of new concepts and innovations for the improvement of basic and fundamental aircraft aerodynamic performance, and hence economy, which leads to the enhancement of lift and the reduction of drag. It is also well known that the trailing vortices which reflect the lift as well as drag characteristics of the aircraft could be optimized for better aircraft performance characteristics and reduction of environmental impact as well as hazardous interference to other flight vehicles and/or objects. Research in enhanced aerodynamic efficiency has led to geometrical modifications, novel devices and features on the aircraft wings, such as blended-wing-body configuration, airfoil profiles and winglet designs, introduction of and/or invention of sensors for identifying relevant physical phenomena or measuring devices, introduction of novel computational methods to assess the prevailing force system with better accuracy through meticulous modeling, and introduction of control system and procedures for wake vortices alleviation and aerodynamic configuration optimization. Typical winglets configuration can significantly reduce the induced drag (in the order of less than 10%) with a resulting increase in wing lift-drag ratio and near the design lift coefficient. The corresponding improvement in lift-drag ratio is more than twice as great as that achieved with the comparable wing-tip extension. As also observed in many aircrafts produced in the last decades, only winglets have demonstrated sufficient benefits to find application on modern airliners. Further enhanced aircraft aerodynamic performance are suggested by introduction of recent innovative designs and patents of winglets, sharklets, blended winglets, capped winglets, s-shaped winglets and spiroidal winglet. The review identifies stability of various configurations of vortices, vortex decay and means of reducing vortex hazard. Passive wake vortices alleviation systems utilize the natural evolution of the instability modes with the highest growth rates while active systems rely on accelerating selected modes of instability by imposing the vortices individually or as a system. The passive system is essentially a vortex wake, hence an aerodynamic surface design, while an active system is an actuator design effort, respectively.
Keywords: Aerodynamics, lift and drag, non-planar wings, trailing vortices, vortex alleviation, wakes, winglets, aircraft, vortex dynamics, vortex decay, vortex pair instability
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