Breakthrough sensors enhance wing aerodynamic performance EU-funded researchers unveiled innovative active sensors that detect flow separation in aircraft wings. The new flight-ready measurement systems will enable engineers to further optimise the aerodynamics of next-generation aircraft. Transport and Mobility © BARBAROGA, Shutterstock For aircraft engineers, controlling laminar flow is the most compelling quest as it helps reduce drag. Laminar flow is essentially the way airflow travels above and below wing surfaces, following smooth parallel paths with no disruption in between. Its counterpart is turbulent flow that occurs independently of the shape and size of wing surfaces. As air moves across a wing, the interface becomes a chaotic region of irregular fluctuations and eddies and pressure increases, causing an increase in the aerodynamic drag and fuel consumption. Detecting skin friction and pressure “Known in the industry as skin friction, or wall shear stress, this force together with pressure are the two signatures of flow physics near the aircraft wing,” notes Julien Weiss, coordinator of the EU-funded SKOPA project. “We designed and fabricated a flight-ready measurement system based on thermal sensors for skin friction measurements and fibre-optic sensors for pressure measurements. The technology may be used to mitigate the effects of flow separation, thereby increasing aerodynamic efficiency and flight safety.” Unlike conventional sensors, the newly developed fibre-optic sensors are less susceptible to external perturbations and noise. In addition, the thermal sensors are designed to detect both the amplitude and direction of skin friction on a wing compared to most sensors that only detect the amplitude. Next-generation aircraft engines Project activities have important implications for the development of quieter, greener and more fuel-efficient engines, such as the ultra-high bypass ratio engines. Such engines have a higher propulsion efficiency but involve the development of relatively large nacelles. Therefore, “to provide sufficient clearance between the nacelle and the runway without introducing longer landing-gear struts, the nacelles must be integrated closer to the wing. This, in turn, increases the risk of flow separation in the region of the wing-pylon interface, especially during take-off and landing,” explains Weiss. Actual flow separation would be particularly detrimental as it would limit both the maximum lift coefficient and the lift-to-drag ratio of the aircraft, two aerodynamic quantities that are critical for landing and take-off, respectively. The EC’s research programme Clean Sky 2 has introduced integrated active flow control techniques at the wing-pylon interface to reduce or eliminate possible flow separation zones. “With our new technology, engineers can validate the effectiveness of active flow control systems and further optimise the aerodynamics of new transport aircraft,” notes Weiss. Project partners used an industrial outer wing model equipped with active flow control to test the response of both sensors. Results showed that the thermal sensors effectively measured the increased wall shear stress generated by the active flow control actuators. The static pressures and pressure fluctuations measured by the pressure sensor matched reference data. After conducting wind tunnel tests, project partners used the Light Aircraft for Science, Education and Research (LASER) of the Technical University of Berlin to validate the flight readiness of both sensors. “Flight tests reveal valuable insight regarding the physics of flight but require fundamental, robust sensing technology. Our miniature pressure sensor that provides accurate measurements over a high dynamic range enables field testing in harsh environments. Fibre-optic sensors are also a promising solution for harsh environments due to the inherent characteristics of fibre-optic systems: no electromagnetic coupling, no corrosion, passive design and unmatched overload protection and stability,” concludes Weiss. Keywords SKOPA, skin friction, flow separation, active flow control, fibre-optic sensors, pressure sensors, ultra-high bypass ratio engines
