Overview
Inspired by the pop up of birds feathers in certain flight modes, the amelioration of aerodynamic performance via a Porous and ELastic (PEL) is based on the concept of reconfiguring/adapting to the separated flow, thereby directly changing the near-wall flow and the subsequent vortex shedding; which can lead to reduced form drag by decreasing the intensity and the size of the recirculation region. This concept of flow control is novel, more efficient than classical actuators, and can lead to significant increase in the aerodynamic performances.
The PEL-SKIN project aims to deliver a novel airfoil coating to improve the global aerodynamic performance and manoeuvrability of future air transport. We propose to investigate drag reduction from a prefabricated coating composed of a densely packed arrangement of flexible fibres that can be attached directly onto a wing or aerodynamic surface, in the region of separated flow.
The project will investigate the performance benefits this technology can deliver for flow at high Reynolds number, relevant for the next generation of aircraft. The research will endeavour to deliver a clear physical understanding of the principle flow control mechanism and an accompanying numerical model of the phenomena, which shall be implemented and tested into industrial aerodynamics software tools; ready for more detailed downstream design work. Although this research is motivated from low to moderate Reynolds number flows, it is expected that the understanding of the physical mechanisms will pave the way to the development of breakthrough control strategies for separated flows at higher Reynolds-numbers for larger aircraft. The success of this project can thus be expected to deliver direct impact on the environment in long-term; where in the EU, it is currently estimated that 25% of CO2 emissions come from the aeronautical sector.
Funding
Results
Aircraft drag reduction inspired by nature
Under certain flight conditions, the outer feathers on the upper side of a bird's wing tend to pop up similar to self-adaptive flaps on aircraft wings. Scientists are exploiting this phenomenon in new technology to reduce drag, fuel consumption and emissions.
Approximately 25 % of EU carbon dioxide (CO2) emissions are produced by the aeronautics sector. Technologies that improve aerodynamics are important in combating this statistic because reducing drag decreases fuel consumption and combustion is the main generator of CO2. Nature is often the source of inspiration for scientists, and the aerodynamics of birds in flight provides a rich source of ideas for aerospace engineers.
The EU-funded project PEL-SKIN (PEL-SKIN: A novel kind of surface coatings in aeronautics) is investigating a novel aerofoil coating inspired by the pop-up of some birds in flight. Scientists have developed an aerofoil coating (a porous and elastic, or PEL, skin) consisting of a densely packed arrangement of flexible fibres able to reconfigure and adapt to flow separation around the wing.
Researchers are exploiting a combination of theoretical, numerical and experimental investigations. Research is focused on low turbulence levels relevant to the flight of unmanned aerial vehicles (UAVs). However, enhanced understanding of physical mechanisms of action should lead to breakthroughs in flow control for more turbulent flow in larger aircraft.
Numerical and experimental studies are speeding the validation of numerical codes, ensuring that the bending rigidity, gravity effects and clamped boundary conditions are correctly represented in the numerical models. Such a reiterative approach is also being used to quantify the effects of relevant PEL parameters on flow.
A theoretical model of a porous medium attached to a circular cylinder has been used to evaluate the influence of the PEL coating on vorticity properties, yielding encouraging preliminary results. In parallel, the team is experimentally and numerically evaluating the parameter values that achieve drag reduction for a small UAV.
Fuel costs can be up to 40 % of the direct operating costs of an aircraft and fuel consumption generates emissions. The coating promises to be much more efficient than classical vortex generators and should significantly decrease the likelihood of stall and vibrations induced by gusts during take-off and landing. The PEL-SKIN promises to significantly reduce drag, making an important contribution to both the competitiveness and sustainability of the aerospace sector.