HPC Impacts Automotive Aerodynamics

Computational Fluid Dynamics HPC demands

Kevin Golsch

Aerodynamics – Energy Center

1 October 2010

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•Stability and Control– At around 150 mph, vehicle

aerodynamics are equal to chassis forces, at 200 mph they are nearly double.

•Speed– At 200 mph, aerodynamics drag

is over 75% of the engine load

– At 200 mph, a 1% drag reduction will increase vehicle speed almost 1 mph

– At Daytona, the aerodynamic drag separating the pole sitter from the first vehicle going home is around 5%.

Importance of Aerodynamics for Race Vehicles

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Wind Tunnel Correlation

•Not only can computational analysis help solve issues difficult to visualize during experimental testing, it can also help correlate data from one wind tunnel test to the next or to actual road conditions

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Championships

•Analytical and Experimental development when combined together effectively, can yield record breaking results.

– 2007 Chevrolet Impala was the first drag race vehicle developed using Computational Fluid Dynamics

– Vehicle won the 2007 NHRA championship in its debut year

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Importance of Aerodynamics to Production Vehicles

•Average passenger cars push enough air at highway speed to consume over 1 gallon per hour, average full size trucks over 2 gallons per hour.

•At highway speeds, aerodynamic drag is around 2/3 of the engine load

– A 10% aerodynamic drag improvement will improve an average passenger car’s efficiency by around 2 - 3 MPG on the highway.

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Importance of Aerodynamic Integration

•Average passenger vehicle pays a fuel economy penalty of approximately 2 – 3 MPG on the highway for power train cooling.

•Front end airflow (FEAF) is the majority of work performed by today’s CFD engineer Front end airflow (FEAF) is the majority of work performed by today’s CFD engineer

– CFD is used to optimize the flow for cooling performance.

•Proper flow predictions require full vehicle geometry, grille detail, and heat exchanger and fan modeling.

– Typical models are around 20M cells.

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Inductions and Exhaust

•Induction and exhaust systems require only 5 – 10M cells and may be the only type of CFD capable of desktop simulation.

•Inputs for these small models still require large full vehicle simulations

•Final designs still need full vehicle simulations for validation

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Importance of Aerodynamic Integration

•Any diverted airflow, such as brake cooling, can also impact fuel economy

•Both aerodynamic and heat transfer effects can be modeled simultaneously and studied to provide for optimal use of diverted air

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High level of integration

•Flow areas that are nearly impossible to study experimentally can easily be visualized at studied with Computational Fluid Dynamics

•Many flow paths are studied in detail during a vehicle’s development

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Acoustic Modeling

•Customer dissatisfies such as unwelcome acoustics can be modeled:

– Exhaust flow noise propagation

– Interior noise predictions• Mirrors

• Windshield wipers

• Window and sunroof buffeting

• Vehicle shapes

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What it takes to study aerodynamics on automobiles.

•To gather this invaluable computational data, highly detailed models are required.

– Models contain nearly all the parts of the automobile that contact the air

– Volume meshing has been steadily increasing in size to more accurately predict the airflow

• Typical aerodynamic computational fluid dynamic models have approached 50M volume cells

• Each 1M cells requires just under 1 GB of memory to solve

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HPC requirements

•Typical transient full vehicle aerodynamic simulation requires 40 - 50 GB of memory and consume up to 3,500 CPU-hour

– Typical cases are run on 128 to 256 process clusters

•Typical full vehicle acoustic simulation require HPC of around twice that of an aerodynamics run

•Steady-state flow rate simulations require only around 30 - 50 CPU-hours, but are still too large to run on a desktop

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Summary

• Aerodynamics is important to automotive companies and the racing industry as it directly impacts fuel economy and vehicle performance

• Large computing resources are required to properly simulate full vehicles

– Full vehicle simulations and accurate vehicle geometry are required to properly integrate the various demands for airflow with aerodynamic drag and lift

• CFD is expected to become increasingly important to automotive companies as areas of opportunity to improve fuel economy and vehicle performance are reduced.