Aerodynamics is the field of airflow and for EVs it’s of crucial importance: at highway speeds, over 50% of energy is spent on pushing the air away. So, getting the aerodynamics right is paramount to increasing range and reducing battery weight, and with it, cost.
But this branch of science is an extremely complex one and OEMs spend millions on wind tunnels, simulation software and experts to squeeze out the last bits of aerodynamic performance. And with time pressure added to the mix, both OEMs and start-ups are looking for cost & time efficient ways to make more significant improvements in a shorter amount of time. In this article, we’ll have a look at how advances in simulation technology are improving the tools they have at their disposal.
Wind tunnel or simulation? Wind tunnels are large installations where fans drive air through a test section in which the car is positioned. In the more advanced tunnels, the ground also moves to get even closer to real-world conditions. But advanced also means expensive, with the high-end tunnels costing well over 100 million euro to build or 5000 euro per hour to rent.
To reduce cost & accelerate the development process, virtual wind tunnels are also used: through computational fluid dynamics (CFD), designers & engineers can analyse the airflow around their car digitally. Knowing the drag coefficient Cd (which denotes the aerodynamic efficiency of a design) before the first prototype is even built, helps to cut expensive wind tunnel time. And as many simulations can be run in parallel and there’s no time lost building & instrumenting prototypes, this can drastically reduce the development time of new vehicles. In a competitive market with new entrants to the EV scene every month, this time advantage is crucial.
Typically, companies will perform the majority of their aerodynamic optimization work in the digital world through simulations. By analysing multiple design alternatives digitally, designers & engineers can balance the aerodynamic gains versus the impact on cost, aesthetics, safety and more. Near the final stages of a development track, physical prototypes are built & instrumented to validate their CFD models and to optimize the last details.
Democratizing aerodynamics simulations
Testing extreme ideas virtually at low cost is of tremendous value for designers. But with a single software license costing up to 100.000€ and the need for an experienced engineer to operate the software, simulations too can become quite expensive. This is one of the main reasons that also simulations are often pushed back to a later phase in the development phase. When an aerodynamic problem pops up, it’s often too late to change much, as most of the design has already been frozen by then.
Luckily for OEMs and startups in the EV scene, more flexible and affordable cloud simulation tools are making it possible to run simulations much sooner, at lower cost. This enables designers & engineers to run aerodynamic simulations as early as the conceptual phase. As soon as the first sketches are converted into 3D models, aerodynamic simulations can be performed.
Automation also plays a crucial role in this “democratization of CFD”: fully automated workflows that require users only to upload a 3D model & specify the velocity, eliminate the need for detailed knowledge of simulation parameters that otherwise need to be entered. No going backward & forward anymore to finetune the computational parameters. And with simulations running in the cloud, many concepts can be launched in parallel, as there are no hardware limitations either.
Automating the design process
Once the results are in, the designers & engineers can analyse and compare results. Flow visualization techniques have come a long way: interactive 3D models showing the aerodynamic wake, 3D streamlines, pressure maps and so on have opened up the complex domain of interpreting aerodynamic results to a wider audience. Still, aerodynamics are a very complex field and the interaction between designers and engineers is crucial to translate simulation results into relevant design improvements.
In that regard, the advent of automated design tools can be helpful too. Artificial Intelligence & Neural Network algorithms, for example, can interpret aerodynamic simulation results and, after an initial learning period to train the network, suggest new shapes.
Or, a technique called “adjoint shape optimization” can be applied. This technique automatically calculates how sensitive a certain goal (usually the drag of a car, but downforce and aero balance are also common) is to the local geometry of the car. In normal terms, it can suggest where to move a surface inward or outward to reduce the aerodynamic drag on the car.
VIDEO EMBED: Aerodynamic Shape Optimization
Wouter Remmerie, CEO of AirShaper: “Using our Aerodynamic Shape Optimization technique, we’ve achieved up to 15% of aerodynamic drag reduction for a major EV start-up in the US. Getting such design input in the early stages of design is crucial to improve the range of EVs”
Such tools not only help to converge to a solution faster, they also can come up with unexpected shapes that can help inspire designers & engineers.
The layout of conventional ICE (internal combustion engine) is heavily determined by their drivetrain: wheelbase, overhang, greenhouse, packaging, interior space, … are all tuned to the packaging, cooling, … needs of the engine.
Electric drivetrains also feature specific packaging needs but they are much more flexible: batteries can be stored in the floor and the electric motors are much smaller. This leads to numerous possibilities for the layout of the entire car, including new shapes that are inherently much more aerodynamic. Dropping the “nose” of a car in favour of a longer, more drop-like shape for the tail for example can work wonders for the aerodynamic drag coefficient. Combine this with the benefits of autonomous driving (where passengers may not even need to face forward anymore) and the design options are myriad.
VIDEO EMBED: Lowie Vermeersch on Autonomous Vehicle Design
Another aspect is the reduced cooling needs: although electric cars also need to cool their batteries and motors, the required gaps & holes to feed the radiators are much less pronounced in EVs. As these typically represent sources of aerodynamic drag, this too is a major area for improvement for EVs.
Aerodynamics are crucial to improving the range of EVs – a highly streamlined design can provide single or sometimes even double-digit improvements in range.
In this article, we’ve seen how new trends in cloud-based simulation platforms are helping designers & engineers to optimize the aerodynamics all the way from the first concept design to the final production version.