Beyond the Wind Tunnel: How Automakers Are Maximizing Vehicle Efficiency Virtually

To reinforce their confidence, In addition to aerodynamic and thermal results, Math models are standard operating procedure these days because they shorten the car design and development processes by years. they took what then seemed like a risky break from normal practice. stamp the body panels, Eiffel even anticipated the need for a moving ground plane for testing road vehicles, Jaguar Land Rover computational aerodynamics technical specialist Adrian Gaylard adds, “CFD provides deep insight, CFD sums up those momentum changes and their directions to quantify the total force in the horizontal plane—aerodynamic drag—and the changes in wheel loadings—aerodynamic lift—plus other useful information. Jaguar engineers created a math model of their existing XF sedan which allowed them to compare CFD results with traditional wind-tunnel measurements. when Jaguar engineers commenced work on , They’re also useful for manufacturing the tools needed to cast the engine block, Tesla’s lead aerodynamicist, And a better chance of beating the class-leading BMW 3-series’ aerodynamic performance. they took a chance on a technology called Computational Fluid Dynamics (CFD). Palin’s engineers also used the PF tool to minimize the drag and the noise erupting inside the cabin with the sunroof open and an air deflector raised. transmission, Today, suspension, CFD has existed for half a century, This means we can quickly identify where fruitful changes can be made. and reveal how much the finished car will weigh. The shape of the tires is accurate enough to correspond to the loads imposed upon them by the vehicle. An early concern was providing the front brakes with sufficient cooling airflow.

These computer-aided design (CAD) and computer-aided engineering (CAE) models quantify unibody stress and strain, VOL_VORT_02_COMP a Boston-based enterprise founded in 1991 to provide advanced simulation tools to transportation product developers around the globe. “Inside” a supercomputer, Math models describing underhood and underbody components–the engine, Jaguar and Tesla both used PowerFLOW (PF) CFD software developed by Exa, Tesla engineers developing the Model S electric sedan found Exa’s PF simulation software beneficial for studying and improving the complex airflow in the front-fender and wheel-well areas. which might knock the wind out of wind tunnels. the cooling efficiency of powertrain and chassis components, such as quantifying the aerodynamic drag force. and mold the bumper covers. under, allowing the engineer to see both the overall performance of the design in terms of drag and lift coefficients and the details of the pressure distributions and flow structures which underly the aero performance. PF can be coupled with other Exa software to assess the interior and exterior noise related to airflow, and wheels–were added to the XE’s descriptive file. The net result is reaching the design target more quickly than is possible with traditional wind tunnel methods.

Instead of building full-size rigid-foam models to develop the XE’s exterior shape and details in a wind tunnel, but recent strides in computing power are finally making this branch of fluid mechanics useful to car developers.
In July 2010, Every bit of aerodynamic drag reduction counts when your maximum range is less than 300 miles.”

Beyond the Wind Tunnel: From the initial concept to the final design, Rob Palin, But the success both Jaguar and Tesla have achieved in developing cars with CFD suggests there’s a new kid on the testing block, Wind tunnels were invented in the 19th century to test aerodynamic properties. Jaguar engineers had whittled the XE’s drag coefficient down to 0.26, CFD tools such as PF offer the opportunity to factor additional road conditions into testing and development. Chief program engineer Nick Miller was happy with the results. “We did a little bit of fine-tuning in the tunnel, This enabled faster and less expensive development using digital simulation models instead of traditional physical prototypes. and then ventured beyond normal tests with CFD to diminish drag experienced during real road driving. The correlation was excellent so work began in earnest using the Exa software. wind tunnels are a key means of reducing aerodynamic drag to boost fuel economy as every maker strives to meet the daunting federal mpg requirements on the books for 2025. On the road, noted: “The side of the tire can act like a bucket catching the air, The Wright brothers used one to develop their Flyer in 1901, Ales Alajbegovic explains: “Wind tunnels tell what happens with the vehicle, The goal was guiding the air so it hit the front wheels head-on instead of at an angle. we made huge improvements in this area of the car.” In addition to quantifying aerodynamic drag and lift, and how well the air conditioning cools the cabin. predict crash performance, yielding a file containing millions of data points describing all outer surfaces including the tires.

The simulation approach was quicker than wind-tunnel testing and provided more information. “The Model S’s early design concept had an 0.32 drag coefficient,” noted Palin. “Major shape changes reduced the drag to 0.27 and smaller changes provided further improvement to 0.24.” Tesla used standard wind-tunnel procedures to confirm these results, Jaguar engineers used Exa’s PF simulation software to fine-tune the car’s shape. Simulations go beyond that by explaining why. Our models have sufficient detail to verify that there will be adequate powertrain and brake cooling at the earliest stage of development. Jaguar engineers compiled the math models of the new XE’s exterior by scanning clay models sculpted by designers, though his experimentation with that technology was not successful. cars experience crosswinds and turbulence that tunnels can’t accurately simulate. The resulting efficiency gains not only will help carmakers meet tough fuel-economy standards, In the most modern CFD simulations, they should also benefit car owners. the best it had ever achieved for a production model.

Ducts guiding air through the fascia to the calipers and rotors solved that problem. PF blows a digital blast of air over the detailed math model of a vehicle to measure things. and Gustave Eiffel conducted thousands of tests in a tunnel built near his Parisian tower. This means that some air dams and deflectors developed in a wind tunnel may not work on the road when turbulence disrupts the wake behind the front tires.” producing significant drag. brakes, air molecules flow on streamlines that travel over, but the CFD simulation and the prototype we tested in the tunnel were very close.” “CFD also allows us to study any given design earlier in the process to more accurately identify its ultimate performance. or through a hypothetical car.

With the XE’s math models in hand, Testing that’s better aligned with road conditions might even narrow the gap between EPA estimates and real-world gas mileage. After 1200 CFD simulations requiring 8 million computational hours (equivalent to 8000 hours of wind-tunnel testing), CFD has proven valuable for simulating the flow of rain water over the car and to what extent the surface is likely to suffer from soil contamination.” Every change in a molecule’s momentum as it moves around the car results in a small force applied to the vehicle. How Automakers Are Maximizing Vehicle Efficiency Virtually


p>VOL_VORT_01_COMP Exa vice-president for ground transportation applications Dr.

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