New knowledge towards the next generation of energy-efficient commercial aeroplanes An EU initiative has improved civil aircraft wings’ aerodynamic performance, leading to a reduction in fuel consumption. Digital Economy Transport and Mobility Climate Change and Environment Industrial Technologies Energy Fundamental Research © Francois Poirier, Shutterstock The EU-funded BUTERFLI (Buffet and transition delay control investigated with European-Russian cooperation for improved flight performance) project advanced the state of the art to enhance the drag, lift and weight performance of aircraft wings. The focus was on flow control principles. Overall, the project studied the experimental and numerical flow control of different phenomena. These include the buffets on laminar and turbulent supercritical airfoils and the cross-flow instabilities on a swept wing. It also investigated various control techniques. Specifically, the BUTERFLI team controlled the buffet on a 2D supercritical wing profile operating in turbulent regime. Only the process using a tangential jet flow control was effective in wind tunnel tests. The dielectric barrier discharge (DBD) actuator check was ineffective. The other plasma actuators by spark discharge exhibited some ability to reduce but not entirely suppress the buffet phenomenon’s amplitude. Scientists characterised and controlled the laminar buffet on a 2D profile. Tests performed on a transonic wind tunnel successfully characterised the occurrence of laminar buffet in the Mach Incidence envelope. A numerical simulation reproduced the laminar buffet’s dynamics. Active control by blowing upstream of the shock delayed the buffet’s occurrence. The passive control by bump 3D demonstrated an attenuation of the phenomenon without completely removing it. Project partners examined two flow control principles using DBD actuators in order to delay the laminar-turbulent transition generated by the presence of transverse flow on a swept profile. BUTERFLI contributed to the design and development of several new flow control technologies. Scientific advances were made in buffet control methods, particularly laminar regimes. Such efforts will contribute to reducing the environmental footprint of air transport, and meeting the emission reduction goals set in Flightpath 2050 – Europe’s vision for air transport by 2050. Keywords Wings, BUTERFLI, buffet, transition delay control, flow control
