About Sharks in Aviation: bionic surface technologies and Lufthansa Group researched Riblet Technology on Aircraft
Sustainability and the reduction of the ecological footprint are topics, that are becoming more and more serious and relevant nowadays.
The Lufthansa Group is also taking a close look at its sustainability goals and has approached bionic surface technologies to jointly implement the know-how in Riblet technology available in both companies in a pilot project.
Responsible for numerous advantages of this technology is the special surface structure consisting of grooves just a few micrometers in size: the so-called Riblets. They are modeled on nature and imitate the friction-reducing properties of shark skin (therefore Sharkskin technology is often used as a synonym, note). If this special surface structure with its friction-reducing properties is applied to the flow-relevant areas of an aircraft, the aerodynamics can be influenced, which in turn leads to lower fuel consumption and Co2 emissions.
To this end, bionic surface technologies worked together with Lufthansa Technik in 2015 to research the perfect solution for long-haul aircraft provided by Lufthansa Airlines, a Boeing 747-400-. In order to be able to demonstrate the utility in detail, the actual state for the 747-400’s aerodynamic conditions first had to be mapped. For this purpose, the exact computer model of the 747-400 went through an extensive basic simulation at bionic surface technologies to generate a “virtual twin”. Subsequently, extensive simulation studies of various roughness at different operating points, which occur during scheduled flight, were carried out.
Only after these important steps could the design of the Riblets, such as structure heights and surfaces, be designed and adjusted with the help of the previous measured values. This also means, that the structure of the Riblet themselves first had to be optimized for various operating points in order to achieve the highest possible output. Further simulation of the Riblets on the 747-400, as well as simulation of the various operating points for the respective Riblet configurations, has now demonstrated how effective these surface structures consisting of grooves can really be for aviation. For example, the application of Riblets to flow-relevant parts of the aircraft with ideally calculated Riblets theoretically saves up to 4% fuel. In reality, up to 3% savings in fuel and corresponding Co2 is possible.
The application of Riblets to the entire aircraft is associated with costs, which could also be reduced by further optimization – without sacrificing fuel efficiency. For this purpose, on the one hand the layout of the Riblet application was again closely examined and adapted, and on the other hand, the Riblet foil itself was again aerodynamically examined and tested. By means of experimental evaluations using a special audited Riblet testbench from BST, the amount of resistance reduction of the Riblet surfaces was tested under various age and abrasion conditions. In this way, it was also possible to evaluate, as part of the certification process, how critical the effects of abrasion and defects are and at what point the foil needs to be replaced in order to develop its full effect.