Apr 2 2019
For a commercial jet airplane, 35,000 feet is considered as a standard cruising altitude. However, the air temperature at those lofty heights falls below –51 °C, and as a result, ice can form easily on the aircraft’s wings.
In order to prevent the formation of ice and thus the resultant drag on the airplane, existing systems use the heat produced by burning fuel. However, these systems, which are dependent on fuel and high temperatures, cannot be utilized on the proposed temperature-sensitive, all-electric materials of state-of-the-art aircraft.
As researchers look for innovate anti-icing techniques, physicists from Iowa State University and Northwestern Polytechnical University in China have adopted an entirely different method. They have reported the study results in AIP Publishing’s journal Physics of Fluids, demonstrating that the importance of equipment in controlling takeoff and landing can also act as icing control.
Current anti-icing methods are not suitable for next-generation aviation systems based on the new aviation technologies. We have found an excellent way to control the icing on these new aircraft.
Xuanshi Meng, Study Author, Department of Fluid Mechanics, Northwestern Polytechnical University
It relies on plasma actuators.
Plasma actuators are regarded as a unique type of short electrical circuit. Upon applying a high voltage across the pair of electrodes, the particles of air above the electrodes are ionized and a plasma is subsequently formed, inducing wind, or flow. Earlier, this flow of plasma over the actuator has been exploited to regulate the aerodynamics of aircraft wings, changing the drag and lift for takeoff and landing (called flow control applications). However, plasma actuators do not simply discharge an induced wind.
When applying a high voltage, most is converted into heat and the rest is converted into an induced flow or ionic wind over the actuator, so the plasma actuator has both aerodynamic and heat effects. By coupling the aerodynamic and thermal aspects of the plasma actuator, we have provided a completely new method for efficient icing and flow control.
Xuanshi Meng, Study Author, Department of Fluid Mechanics, Northwestern Polytechnical University
At the Northwestern Polytechnical University, the plasma control team initially realized the impact of plasma actuators on icing earlier in 2012. The team observed this phenomenon when an ice cube placed in the plasma exciter’s discharge area melted rapidly.
In order to further elucidate the mechanism of the protection of plasma ice, the team created surface dielectric barrier discharge plasma actuators that were extraordinarily thin and then mounted them on a plastic NACA 0012 airfoil, which was printed in 3D.
In order to examine how different aerodynamics affected the formation of ice, three configurations of actuators were installed, Afterward, high-speed cameras, alongside infrared thermal imaging as well as particle scattering lasers, were used for observing the way the induced flow and thermal output interacted together.
Subsequently, tests were performed under still air conditions and also within an icing wind tunnel, in which cold particles of air were aimed at the airfoil. The researchers discovered that flow and thermal dynamics are inseparably interlinked for all the three actuators.
It was observed that the plasma actuators, which were located perpendicular to the surface of the airfoil, were the most effective at transmitting heat along the aircraft wing, fully preventing the formation of ice. the team compared the transfer and flow of heat between the varied designs and eventually reached a conclusion that the optimal design have to produce as much heat as possible locally and, at the same time, it should combine suitably with the incoming airflow.
This could be used to design an effective anti-icing system at low enough temperatures to prevent stress on the composite material design of next-generation aircraft.
Xuanshi Meng, Study Author, Department of Fluid Mechanics, Northwestern Polytechnical University
Afaq Ahmed Abbasi, a student of Meng, added that “The conventional anti-icing technique uses air as hot as 200 degrees Celsius to vaporize the water droplets, and composite material cannot afford such high temperatures. But the plasma icing control can stop the supercool droplets forming ice on the surface of the vehicle without temperatures as high, which is good for the composite materials.”
Meng further informed that his team’s proposal to utilize plasma actuators as anti-icers came as a “surprise” for fluid mechanics experts. Nevertheless, he conceded the fact that they are still at the nascent stage of the study and that more research needs to be done to identify how thermal and flow effects are interlinked, and how accurately they operate together to dissipate supercooled droplets from the surface of a wing.