Wuthering heights

The lights come on and a lift raises a Škoda Enyaq RS iV into the room. The wind tunnel is ready to measure the final version of this all-electric SUV. Let’s do it!

24. 11. 2022 Škoda World

The white car is partly covered with black foil, with green pieces of string hanging from red dots. A cotton string test is about to start. Rollers in the floor turn the car’s wheels and the tunnel operator switches on a giant fan. Soon there is a noticeable wind passing over the car and the pieces of string begin to flutter.

“By tracking the movement of the cotton strings, we can determine the airflow on the surface of the car,” explains Jiří Novák, chief aerodynamicist for the Enyaq iV project at Škoda Technical Development. In this test, like in all others, the wheels are made to spin because their movement also affects the airflow around the car.

And it is making the airflow around the car and its parts as uncomplicated as possible that the aerodynamics experts want. “The goal is to keep the c_d drag coefficient as low as possible. Reducing it means lower fuel consumption and, of course, a longer range per charge in an electric car,” says Zdeněk Sloupenský, external aerodynamics coordinator for the MEB platform.

The car ready for testing in the wind tunnel

This time, it is a pre-production Enyaq RS iV that is standing in the tunnel at the University of Stuttgart. Approximately nine-tenths of the aerodynamics development work is done virtually using computer simulations, which are assisted by the super-powerful HPC computer used by Škoda. Yet this is not the first time the aerodynamics experts have come across this car in real life. They have already been in the tunnel with a 1:1 scale model and a working prototype. Virtual simulations help to understand what is happening in the flow around the car and why. Measuring in the tunnel is the culmination of the entire development and confirms the development process that was built on calculations.

Airflow test using cotton streamers

The aerodynamics experts share the results of the calculations and measurements for models and prototypes with their colleagues in design and construction. They then work together to find solutions that are acceptable to everyone involved and help to improve the performance of the car being developed. “We work together throughout the car’s development. From discussing the car’s basic lines and proportions to detailed adjustments to the bumpers and rear-view mirrors. Even a tiny change that reduces the drag coefficient by one hundredth will increase the Enyaq iV’s final range by approximately 7 kilometres on the WLTP cycle. In the case of motorway driving, the increase is even more significant,” says Zdeněk Sloupenský.

But what’s the point of measuring a pre-production car? There’s nothing that can be done about its shape. “Under the current WLTP homologatio n regulations, we are obliged to evaluate all aerodynamically relevant configurations that are optional on the car, such as the wheels, before it is registered for the first time. And this is done on a pre-production car,” reveals Zdeněk Sloupenský.

The wheels have to turn during wind tunnel testing because wheel movement affects airflow around the car

But let’s take a look back at the cotton strands that can flutter in winds of up to 60 km/h. Their movement is recorded by sensitive cameras, and the recording is then used to produce a map of the airflow at specific points on the body, for example on the fender behind the front wheel or around the luggage compartment door. Correctly directing the airflow not only reduces the aerodynamic coefficient, but also makes it possible to protect important parts of the bodywork from dirt on the road, for example.

The wind has stopped and the cotton threads have calmed down again. Something new is about to happen. A smoke probe – a device that emits artificial smoke – is brought on. When the smoke is blown from in front of the car, it follows the profile of the body perfectly, showing how the air flows around the car.

Smoke pattern test - here the airflow around the entire body is clearly visible

Of course, the smoke probe does not only test the entire body, but also the individual elements of the body that aerodynamics experts are particularly concerned about. The front bumper, the exterior mirrors and the wakes behind them, the wake behind the rear window, the air-curtain, that is, the design element on the sides of the front bumper that channels the air around the front wheel. The smoke stream will test all these areas and confirm that the air flows around them as the experts intended.

“Aerodynamic drag is largely determined by the shape of the wake behind the car. It is an area of slowed airflow with a direct effect on the rear of the car. The aim of aerodynamics is to achieve a symmetrical shape of the wake and thus the highest possible pressure on the rear,” explains Jiří Novák.

The smoke clears and a giant ridge comb around the car. But don’t expect any hairstyle adjustments. The so-called comb probe is another measuring device that finds use in aerodynamic testing. The teeth of the comb behind the car measure the speed of the airflow and the result is a view of the flow in the area further away from the car. “By analysing the velocity of the flow, we get information about its turbulence. In addition to the aforementioned wake, the probe also monitors the behaviour of the airflow behind the wheels. The wheels’ movement creates a complex aerodynamic phenomenon. The aerodynamics team’s aim is to achieve a smooth flow around in this area,” says Jiří Novák.

Visualisation of the rear spoiler wake

The aerodynamics experts at Škoda Technical Development are very good at their job. The latest Škoda models boast excellent aerodynamic properties and excellent c_d index values. The Octavia, with a value of 0.24 (Octavia Combi 0.26), is among the best in its class, as is the current generation Fabia. The Enyaq iV, with a coefficient starting at 0.257, is at the top among SUVs, and the recently launched Enyaq Coupé iV scores even better at 0.234 thanks to its slanting rear end.

In addition to optimised shapes of bodywork, bumpers, mirrors or the aforesaid air-curtains, the smooth floor covered with aerodynamic panels and the smooth shape of the battery pack offer great potential in electric cars. Another way to reduce overall drag is to intelligently control the amount of air entering the engine compartment by means of an adjustable shutter located in front of the cooling pack.