The aviation industry (passenger and freight), which currently accounts for 2.5% of the global CO2 emissions (1.9% of global greenhouse gas (GHG) emissions), is continuously under pressure to reduce its environmental footprint, given its historical and forecasted environmental track, strongly affected by the remarkable air traffic volume increase rates, albeit with a slower growth in emissions, due to the massive aviation's efficiency improvements, driven by the in the design and technology(more efficient and larger) aircrafts; improved operational practices and increased load factors (more passengers and freight per flight). Nevertheless, it has not been enough to tackle the rapidly increasing CO2 emissions (26% in the 2013-2018 timeframe and expected to continue increasing), which ultimately could grow between 2.4 and 3.6 times by 2050. This scenario has driven governments and the aviation industry to adjust their short term actions and develop a long-term decarbonization agenda, aligned with the Paris Agreement targets. To reach the environmental compromises, the aviation industry is required to bring fleet wide average fuel efficiency improvements of 2.5% per year, from 2020 to 2050, associated with the use of low carbon energy, such as certified sustainable aviation fuels (SAF) and, in the longer term, electric propulsion for specific aviation niches.
The continuous efficiency improvement requirement relies on technological strategies, such as the reduction of aircraft weight (through the use of lighter and more resistant materials), engine propulsion (thermodynamic and propulsive) efficiencies, as well as aerodynamic (drag reduction) improvements. While the aviation has already delivered acknowledged improvements in the formers, aerodynamics still has a large improvement potential for commercial (subsonic) aviation, focused on the reduction of the skin-friction drag and lift-dependent (induced) drag, those with the larger effect on the aerodynamic efficiency of aircrafts.
In this context, important progresses have been achieved in the design, development, testing and use of practical aerodynamic and manufacturing technologies, focused on the aerodynamic improvement of airplanes, as a tool to make aviation more environmentally sustainable. The prospective aerodynamic technologies include the use of wingtip devices (winglets and raked wingtips), supercritical airfoils, associated with adaptive wings, as well as the use of laminar and/or conditioned turbulent boundary- layer flow on portions of wings, nacelles, tails, and fuselages, with the so called Natural Laminar Flow(NLF) or Hybrid Laminar Flow Control (HLFC). Moreover, adaptive (morphing) wings (using control surfaces) might also provide structural wing load alleviation, and, hence, weight reduction, for a given wing span. It should be noted that some of these technologies are already used or are under test on some prototypes, based on current commercial aircrafts.
This work gathers, into a unique source, an overview of the aerodynamic strategies of the aviation industry to reduce its environmental footprint, with a technological review of the state of the art aerodynamic technology and the tools to improve the aerodynamic efficiency, followed by a snapshot of some of the ongoing research, developmental flight testing and commercial use of aerodynamic optimization devices, with their inherent efficiency improvement potential.