How Testing & Simulation at Volvo Trucks Improved Aerodynamics.
Overcoming air resistance significantly contributes to a truck’s fuel consumption when driving at speeds from around 50-60 km/h. Furthermore, its effect on fuel consumption increases exponentially the faster you go. Aerodynamic design has, therefore, long been one of Volvo Trucks’ most important focus areas when it comes to reducing the fuel consumption of its vehicles. Its engineers continuously work with wind tunnels and simulations to identify further improvements. One of their key aims is to delay flow separation. This is when a layer of airflow detaches from the truck’s surface. The earlier it detaches, the larger the wake behind the vehicle and, therefore the higher the pressure drag. Minimising and delaying flow separation, therefore, minimises pressure drag.
Two types of air flows to have in mind: aligned and separated.
“The flow greatly accelerates as it goes from the stagnation point in front of the truck (high pressure) over to the sides (low pressure),” explains Anders Tenstam, Aerodynamics Specialist, Volvo Trucks. “If a truck is driving at 90 km/h, then the flow velocity at the corners can reach speeds as high as 200 km/h. This makes the front corners a susceptible region, and any small object or gap can hugely impact the overall airflow.”
In their most recent simulations and tests, Volvo Trucks’ engineers were able to identify several small gaps and split lines on the truck’s exterior that could further improve aerodynamics if sealed.
“We could see that split lines and gaps can be crucial depending on where they are situated,” says Mattias Hejdesten, Engineering Specialist Aerodynamics, Volvo Trucks. “They allow airflow to seep in behind the front panels, which then gets sucked out in the low-pressure regions on the cab’s sides. From there, it can trigger flow separation when interacting with the external air flow.”
To help stem these leakage flows, new seals have been placed between the various front panels. As a result, any triggering of flow separation at the vehicle’s front corners is eliminated, helping the external flow to stay attached to the vehicle’s sides for longer.
“Truck aerodynamics is a lot about mastering the small details,” says Anders Tenstam. “The truck cab is a workplace with many legal restrictions and considerations, so there is a constant battle for every millimetre of available space, to accommodate all essential functions.”
By adding these seals, not only does it improve overall aerodynamics, it also opens up additional opportunities for improvements further along the vehicle. These improvements include adding an extended door extension to fill the void in the footstep box. This creates a flat surface for the external airflow to attach to, thus further reducing flow separation. In addition, using wider wheels and mudguards create more alignment, while a new fender flare reduces the gap from the wheel. This results in reduced evacuation flow from the wheelhouse and, by extension, less aerodynamic drag. Finally, new curved designs for mirror arm covers with smaller peak holes also help reduce flow separation.
“By improving the conditions at the front of the truck, we can suddenly see some opportunities to maintain an aligned flow along the sides too,” explains Mattias Hejdesten. “Otherwise, if we had not done this, we would have seen minimal benefits from these additional aerodynamic improvements.”
While each update will contribute to improving the vehicle’s energy efficiency and reducing fuel consumption, the savings generated when combined in one package will be greater than the sum of all parts.