Aerodynamics vs Cooling : active grille shutters

The aerodynamic quality of a vehicle has become (again) a sales argument. You cannot call it a new trend; it has been up there for decades already. But electrification being on the fridge of mass adoption, automakers claw for any solution that would extend the vehicle range, and aerodynamics is one of them. While the overall shape of a car drives its performance, certain design features can contribute. Active front grille shutters are one of them.

The front grille guides the air towards the radiator and the engine / motor compartment and protect them. A large opening would increase the airflow rate and improve the radiator cooling but at the expense of turbulence or complex air guides in the engine compartment. On the other hand, shutting down the front end reduces the aerodynamic drag but air-cooling efficiency as well. Active shutters offer a compromise. They dynamically adjust the grille flap position. Depending on the situation (speed, A/C on or off, HV battery active cooling…), they open or close the vehicle front end and can potentially provide the best of both world. That is, if you exclude aerodynamic noises occurring when air flows through narrowing inlets.

Looking at A2Mac1 data, the active shutters were first observed on internal combustion engine vehicles, end of the 2000’s. Fuel consumption and CO2 emission of ICEV were to reduced. Across time, on ICEV and BEV, we observed different design strategies with several main drivers in mind : compactness, weight reduction, protection of the actuator, its driveline, and electronics. Additional characteristics our data acquisition team could pick up include actuator speed(s), current(s), torque(s). Here are a couple of examples showing the diversities of solutions from various manufacturers.

Time to digress and talk about suppliers. On the pictures above, I purposely mentioned the names of the actuator manufacturers. A2Mac1 benchmarking data is a sort Who’s Who of the automotive industry. Whenever OEMs keep their supplier’s logo on the parts we photograph, or we can recognize their specific part numbering convention, we can tell who supplies what, where to whom. We open the door to valuable use-cases for OEMs (alternative sourcing, supply chain localization) and suppliers alike (growth potential assessment, competitor review). Here is an example showing the Top 5 suppliers of shutter actuators we observed in 176 vehicles from 2008 until now :

Back to technical execution. We analyzed Tesla Model Y inside out and it is equipped with active flaps. The aerodynamics studies we conducted assumed the shutters were closed and we could do run a similar CFD simulation in an open configuration, should you, dear Reader, be interested. On top of that, our Energy Management Service studies replay various use-cases (WTLP, RLE, tracks, dyno tes beds) hence various vehicle speeds. It makes it possible to figure out the logics implemented by Tesla. Aerodynamics (closed flaps) vs. Cooling (open flaps), which one prevails ?

Granted, we pick up 200+ channels and multiple use-cases but I assumed the temperature in the middle of the radiator front face, the vehicle speed and the flap opening (0% being closed, 100% being fully opened) were a good-enough selection to understand the system logics. Based on 15-or-so open road driving and dyno use-cases I reviewed, my conclusions are as follows:

1. By default, on the road, the shutters are closed,
2. The flaps operate stepwise : close, 1/3, 1/2, 2/3, or fully open and do not continuously adjust the flap angle,
3. If the temperature spikes above 20°c, the flaps will open whatever the speed (other use-cases showed the same behavior at higher speeds than the one above),
4. The shuttes go from close to open positions in about 5 seconds,
5. At very high speeds (130-180km/h) and high radiator front temperatures, the flaps remain open (not shown on the graph above),
6. Even at low radiator temperatures, at relatively low speed (under about 60 km/h), the flaps can open for an extra “burst” of cooling.

Conclusion : cooling considerations prevail over aerodynamics.

It will be interesting to analyze the test results of the Volkswagen ID.3. It uses a dynamic sliding curtain, and it is uncommonly located after the radiator. Different implementation for a different logic. You can run these analysis on your own with our data. Reach out to me or my colleague Rapha?l Andrei to know more.

To know more about Dynamic Benchmarking including our Aerodynamics analysis, feel free to contact Vincent Kéromnès.

To know more about A2Mac1 and our Benchmarking consulting offering such as Vehicle Discovery Reports, feel free to contact me at [email protected].

Opinions are mine and do not express the views of my employer.