Making aircraft more energy-efficient with better flow control
Aviation emissions are among the fastest-growing sources of greenhouse gases. As passenger demand continues to grow, innovative solutions making aircraft greener are vital to achieving climate neutrality. Optimising aerodynamic performance can make an important contribution to reducing aircraft energy consumption, while also improving their stability and reducing noise levels. Fluid (Flow control) is a key research focus in this context. The EU-funded PERSEUS project has now delivered a methodology for optimising the design of a device controlling the flow of air to reduce so-called flow separation. This phenomenon occurs when the flow of air ‘detaches’ from the surface of the aircraft, impacting performance. “There are a number of situations where the appearance of flow separation is observed,” says Nicolas Mazellier, professor of Fluid Mechanics at the University of Orléans, the project host. “It occurs during manoeuvres such as take-off and landing, and also where obstacles disturb the flow, for instance at the junction between the wing and nacelle.” Flow separation creates areas of turbulence producing vibrations and noise, increases emissions and can result in instabilities. In extreme cases, it can affect the pilot’s ability to control the aircraft: “A stall is one of the most dramatic consequences of massive separations,” Mazellier notes.
More efficiency with active control
The PERSEUS team took a novel approach to tackling this issue. They developed a methodology taking the problems appearing at the wing-nacelle junction as the starting point and using the equations in fluid mechanics to guide the design of an optimised fluidic actuator for flow control. Such actuators are used on aircraft to manipulate airflow in a variety of situations. The pulsed jet actuators developed by Mazellier’s team generate fast air jets to reduce the effect of flow separations while using as little energy as possible. “So-called active control makes it possible to regulate the flow only when it is necessary to achieve high effects at the lowest energy cost,” Mazellier explains. This is a real challenge, he adds: while existing systems are effective from an aerodynamic perspective, they add significant weight and are difficult to manoeuvre.
Net energy gains of up to 20 %
The pulsed jet actuators used in the PERSEUS project could overcome some of these defects. Bringing together know-how in fields including micromechanics, microfluidics and high-fidelity numerical simulation, the team was able to perform one of the very first high-fidelity numerical calculations of the internal flow of an actuator. “By tackling this major scientific challenge, we have learned a lot about the physics of the switching process which is at the origin of the bistable character of the pulsed jet actuators we have developed,” Mazellier notes. Numerical modelling was combined with wind-tunnel testing to optimise the internal design of the actuators. Containing no mechanical parts, they are extremely reliable. Tests have shown the high efficiency of the control strategy at a low operating cost, with potential net energy gains of up to 20 % in the critical phases close to a stall.
The sky is not the limit
Bringing PERSEUS’ innovations to the market will require further research to scale up the tools developed in the lab and get them ready for deployment at an industrial scale. In addition to helping solve an aeronautical problem, PERSEUS’ methodology could have applications beyond this sector. The optimisation techniques it enables show promise for helping curb energy consumption in other areas such as heating and cooling systems.
Keywords
PERSEUS, aerodynamic, flow control, flow separation, fluidic actuator, pulsed jet actuator, aviation emissions, turbulence
