Electric wind takes truck aerodynamics from brick to slick
Researchers at Sweden's KTH Royal Institute of Technology are developing a device that increases the fuel efficiency of trucks by cloaking them in electric wind. Using plasma actuators to charge the air, the new technology controls the flow of wind around the truck to reduce drag and could improve fuel consumption by five percent.
According to the American Trucking Association, 70 percent of heavy freight in the US alone is moved by trucks – that's 10.5 billion tons of cargo on 3.4 million heavy-duty Class 8 trucks. Worldwide, that not only translates to a lot of stuff hauled by a lot of trucks, but also a lot of fuel burned.
The basic truck is a moving crate that's about as aerodynamic as a brick. As it travels down the highway, it doesn't so much slide through the air as rip it up and fling it churning to the side, which is one reason why passing a juggernaut in the pouring rain is such an unpleasant, if not frightening, experience.
Engineers have been aware of this shortcoming since the 1920s and have developed any number of ways of streamlining trucks to make them more aerodynamic. This makes them faster and more stable, as well as more fuel efficient. However, there's still a long way to go, so KTH is taking a page from aerospace engineering.
Aircraft, too, have problems with drag. When a plane is taking off, for example, the increasing angle of attack causes the air to flow less smoothly over the top of the wing and breaks up into turbulence. Engineers get around this by fitting winglets to the tips of the wings to generate vortices that increase lift. KTH wanted something similar for trucks to reduce drag. The snag is that trucks, obviously, aren't airplanes.
What the KTH team came up with is a way to generate vortices at the front of the truck cab to control air flow, but instead of using metal vortex generators like winglets, they used electric wind.
The idea is that as air strikes the front of the truck, it flows around it, forming a boundary layer that, if the truck is aerodynamic enough, follows the surface cab and cargo area until it reaches the back and breaks up into eddies. If the truck is moving through still air, that's okay, but if there's wind striking the vehicle at an angle, it can slow down the boundary layer, causing it to separate and form turbulence.
The KTH system uses plasma actuators on the front of the cab. These are two high-voltage electrodes that ionize the surrounding air molecules and accelerates them through the electric field to generate wind without the need for moving parts or protruding airfoils. In addition, these actuators can be adjusted to counter the specific strength and direction of an incoming wind by setting up vortices that force the air into the boundary layer, lowering drag.
"Our ultimate goal is to reduce the flow separation that occurs on the front corners of the truck," says KTH researcher Julie Vernet. "By adding momentum close to the surface, the size of the separated region is reduced."
The video below illustrates how minimizing cross winds on trucks increases efficiency.