Aircraft impose burdens on the environment in the form of noise and emissions, and the effects are often interrelated. Technologies to reduce one can often lead to reductions in another. Such is the case with minimising drag and enhancing laminar flow over aircraft surfaces. The Advisory Council for Aeronautics Research in Europe (ACARE) and the Quiet Aircraft Technology programme in the United States have both set stringent goals for reductions of noise and emissions with deadlines in the near future. The EU-funded project CLFCWTE contributed to the effort to meet those deadlines through investigation of a closed loop flow control methodology. Their aim was to minimise boundary layer separation on a trailing-edge wing flap. The boundary layer is the layer of flow in the immediate vicinity of the wing surface. It is subject to significant viscous effects, and when it separates from the wing it creates a large increase in drag. Scientists investigated active control of air flow through the use of intelligently applied pulsed jets of air at the leading edge of the wing flap. Position-based pressure distribution measurements were used as feedback to update the compressed air pulses and fast-switching solenoid valves via a novel iterative learning control algorithm. The system was tested in a small wind tunnel. Results demonstrated that actuation delayed separation and increased lift by approximately 20 %, even when faced with sudden changes in the location of imminent separation. The novel algorithms for closed loop flow control on high lift wing configurations are beyond state of the art and expected to make an important contribution to civil aviation. CLFCWTE outcomes will help reduce noise, fuel consumption and emissions for greener aircraft in the near future. These benefits will be felt by people living near airports and help airlines meet environmental regulations to maintain a competitive position.
Pulsed air, wings, air flow, aircraft, noise, emissions, minimising drag, laminar flow, closed loop flow control, boundary layer separation, wing flap, pulsed jets, civil aviation