It's common to see line-shaped clouds in the sky, known as contrails, trailing behind the engines of a jet airplane. What's not always visible is a vortex coming off of the tip of each wing — like two tiny horizontal tornadoes — leaving a turbulent wake behind the vehicle. The wake poses a destabilizing flight hazard, particularly for smaller aircraft that share the same flight path.

Wake turbulence from a jet airplane wing. (Ryoh Ishihara)

Although most wing shapes used today create these turbulent wake vortices, wing geometries can be designed to reduce or eliminate wingtip vortices almost entirely. Research demonstrated vortex and wake characteristics computed for three classic wing designs: the elliptic wing, and classic wing designs developed by R.T. Jones and Ludwig Prandt.

The elliptic wing configuration has been used as the gold standard of aerodynamic efficiency for the better part of a century. It has optimal loading characteristics, and is often used when looking at wing efficiency for minimizing drag. In a previous experimental study on optimizing wing configurations, researchers discovered that gain efficiency of the wing system can be optimized with a non-elliptic wing profile.

In this work, the flow about the three wings was simulated, showing significant differences in how the vortices and wakes developed from each of the three wing types. The Jones and the Prandtl wing configurations did not have wingtip vortices like the elliptic wing; they had a much more gradual bulk deformation of the whole wake structure, rather than an immediate coherent roll-up. The formation of wake vortex structures can be delayed, and the distance it takes a trailing wake vortex to roll up can be increased by about 12 times, making it weaker and less of a hazard to the aircraft entering its wake.

The information can be used to re-tailor how formation flight is viewed between aircraft, or to develop an ideal configuration for lift loading for takeoffs and landings, and subsequently reduce the length of separation between aircraft in the same flight path. The motion of the air produced by vortices can create a hazard for trailing aircraft, as it can be unpredictable and make for dangerous flight regimes. Using the Jones or Prandtl wings would result in much less turbulent air behind a plane.

The choice of wing design depends on constraints; for example, wing span and weight.

For more information, contact Phillip J. Ansell at This email address is being protected from spambots. You need JavaScript enabled to view it.; 217-300-0949.


Tech Briefs Magazine

This article first appeared in the October, 2018 issue of Tech Briefs Magazine.

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