An Experimental and Theoretical Investigation of Novel Aircraft Drag Reduction

Abstract

Air transportation is an important part of the world’s economic and indispensable transportation system. The major institutions in the world and the aviation authorities are well aware of the demanding expectations of the public for cheaper transportation cost and at the same time the need to reduce the negative impact of aircraft or air-transportation system on the atmosphere which include noise around airports and global warming to attain sustainability, reduction in the emission of green-house gases such Nitrogen oxides (x) and Carbon di-oxide. In order to achieve such a balance in the future, a strategy is required to match competitive excellence dedicated to meeting the demands of society while at the same time being cost effective for the airline companies and operating aviation authorities. Such a vision or concept cannot be realised without making further technological breakthroughs in engineering fields such as Aerodynamics and other discipline including materials and structures. Improving aircraft aerodynamic performance will have a direct impact on helping to implement these goals. Improving aircraft drag capabilities remains one of the big challenges faced by manufacturers of transport aircraft. It is known that for a typical transport aircraft drag, the induced drag amounts to about 40% of the total drag at cruise flight conditions and about 80 –90 percent of the total drag during aircraft take off. The skin friction drag constitute approximately one half of the total Aircraft drag at cruise flight configuration making up most of the remaining percentage of drag at cruise condition. The use of winglets or other wing-tip devices as a drag reduction device play a significant role in improving aircraft performance by acting as passive devices to reduce drag and enhance aircraft performance. In this thesis, four novel spiroid drag reduction devices are presented which were designed and optimised using STAR-CCM+ Optimate + which uses the SHERPA search algorithm as its optimisation tool. The objective of the optimisation process was set to maximise the lift-to-drag ratio. A low fidelity mesh model was used during the optimisation and the results were verified by using high-fidelity physics and mesh model. The developed devices showed an improve CL/CD ratio of up to 11 percent and improved CL by up to 7 percent while reducing CD by up to 4 percent with an 18 - 24 percent reduction in induced drag observed as well. The devices showed consistency in performance at several Mach numbers and angles of attacks. Thus, suggesting that such devices could be used over a wide range of flight regimes on aircraft or UAVs. The study also successfully demonstrated the capability to using this optimisation process in the design and development of such devices. Furthermore, a numerical investigation and wind tunnel verification study was performed on a wing tip turbine to ascertain the aerodynamic performance modification of using such a device at several Mach numbers, angles of attack, propeller rpms and sensitivity of propeller nacelle positions at the wing tip. The obtained results revealed a trend on the nacelle position to achieve the most improved aerodynamic performance. A CL/CD ratio improvement of up to 7 percent, CL modification of approximate 4 percent and CD reduction of up to 4 percent were achieved. In addition to demonstrate an appreciation of some of the wider implication of installing wing tip devices, a flutter analysis on a rectangular clean wing with added variable mass at the wing tip was performed. The result showed that the added masses had no significant implication on the flutter characteristics of the wing.