APPLUS IDIADA uses Simcenter STAR-CCM+ to Provide Driving Range of 250 Miles for EV Compact SUV
Applus IDIADA designs the most aerodynamic electric vehicle (EV) compact SUV, delivering a 0.19 drag coefficient and driving range of 250 miles
Range anxiety is all the rage
“Range anxiety” is the fear of running out of a battery charge and being stranded miles from an electric vehicle (EV) recharging station. Range anxiety has existed since the dawn of automobiles, when there was no network of gas stations and people drove around with gasoline cans strapped to their cars. Today the average person drives only 40 miles per day, yet a recent Forbes study found that due to highway driving, two-thirds of potential EV consumers want a range of atleast 300 miles per charge.
A recent Tesla study notes that a 10 percent improvement in aerodynamic performance gives a 5-8 percent increase in range for EVs. At speeds over 130 kmph (78 mph), around 80 percent of the power is used to overcome aerodynamic losses. Clearly, better aerodynamics provides increased range. Wind resistance is the major contributor for EV performance losses, meaning aerodynamic improvement is twice as important for EVs compared to ICEs. The most aerodynamic cars currently on the market – including Tesla Model S, Mercedes CLA, BMW 5-series and Audi A4–all have Cds hovering between 0.22 and 0.24, depending on engine types and features.
Can an electric vehicle design have a Cd lower than 0.2 without sacrificing form and functionality? The answer from Applus IDIADA, a worldwide leader in design, testing, engineering and homologation services to the automotive industry, is a resounding yes. Applus IDIADA recently unveiled the CRONUZ project, an EV compact sport utility vehicle (SUV) concept car with a Cd of 0.19.Designed with a battery pack of 200 liters and weighing 1,500 kilograms (kgs), the four-seater C class SUV runs on two electric motors and is designed for a range of 250 miles (400 kms).
“As far as we know, this is the first concept electric SUV on the market with a Cd below 0.2,” says EnricAramburu, fluids engineering product manager at Applus IDIADA.
“I can’t imagine conducting a project like this without Simcenter STAR-CCM+. By building a digital twin, we were able to try out various design possibilities with simulation early in the process. Simulation is the key to design innovation.” Enric Aramburu Fluids Engineering Product Manager Applus IDIADA
Breaking the 0.2 Cd barrier with simulate-innovate-test approach
The design was a result of seamless cooperation between Applus IDIADA’s designers and aerodynamicists. The designers produced an initial surface attuned to EV design sensibilities, aesthetically pleasing style, a minimalist aerodynamic design and a streamlined SUV type body. The aerodynamicists then used a virtual wind tunnel with Simcenter STAR-CCM+, a computational fluid dynamics (CFD) tool part of the Simcenter™ portfolio from Siemens PLM Software, for analysis of the vehicle aerodynamic performance using numerical simulation.
Applus IDIADA simulated more than 600 design proposals over six months, progressively incorporating drag-reducing concepts into each design. With Simcenter STAR-CCM+ simulations, the final optimized design delivered a drag coefficient of 0.17 in free air without attempting to model the wind tunnel and in steady state conditions. The final assessment of the wind tunnel testing provided a Cd of 0.19, confirming the simulate-innovate-test approach and the CRONUZ’s place as the most aerodynamic concept EV compact SUV.
Aramburu adds,“We knew from Simcenter STAR-CCM+ that we could achieve a record drag value even before building a prototype.”
Simulation ushers in aerodynamic innovations
Two innovative features on the CRONUZ are key in driving down the drag – active systems and an optimized wheelhouse/underbody design.
Active aerodynamic systems refer to parts of a car moving in-operation to positively affect the airflow around the car. These systems are the next breakthrough in achieving fuel efficiency, reduced drag and increased downforce in the automotive industry. They ensure optimum aerodynamics for every driving situation, be it low drag in economy mode or high downforce in sport mode, while maintaining the design sensibilities and styling requirements from the designers.
CRONUZ features active systems for the front fairing and an active rocker, which are hidden at low speed and while parking. At high speeds or on-demand, the active systems are deployed, changing the airflow around the car (and the car’s shape, in fact) to stay attached from front to rear while minimizing turbulence around the wheel well, one of the key drag contributors.
Forty percent of aerodynamic losses come from wheelhouse and under body areas, offering significant room for optimization. An optimized rim design, low undercarriage (deployed after 80 MPH) and an almost completely closed wheelhouse from underneath minimize wheelhouse turbulence and ensuring attached flow from front to rear – a major driver for drag reduction.
Steady state simulations in Simcenter STAR-CCM+ showed the active systems reducing drag by 20 (one drag count equals a Cd of 0.001) counts. Even accounting for wind tunnel mounts and unsteadiness, which were not included in the simulations, this confirmed the huge reduction in drag from active systems. Wind tunnel tests eventually showed a 14-count reduction.
These innovations were possible by iterating various designs for the active systems, rims and underbody wheelhouse covers in SimcenterSTAR-CCM+ to find the best performing combination. These design improvements reduced drag by 55 drag counts prior to building the only prototype.
The most aerodynamic concept EV
“I can’t imagine conducting a project like this without Simcenter STAR-CCM+,” says Aramburu. “By building a digital twin, we were able to try out various design possibilities with simulation early in the process. Simulation is the key to design innovation.”
The aerodynamic innovations in the CRONUZ stand to help both major original equipment manufacturers (OEMs) and EV startups in reducing drag and increasing range. Such shape-shifting cars with active systems, which have become prominent in the last decade, seem to be the future of automotive aerodynamics.
“As far as we know, this is the first concept electric SUV on the market with a Cd below 0.2,”
Fluids Engineering Product Manager
Guest Post by Prashanth S. Shankara
Siemens PLM Software