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Air is not the only medium encountered by a vehicle on the road. Vehicles must be designed to handle the sometimes harsh natural conditions found on the road, where water, snow, ice, dirt, rocks and other particles of debris are kicked up off the road by tires or wind, or are present due to weather conditions. The small size of these particles dictates that they will be strongly influenced by vehicle aerodynamics. The exterior air flow around a moving vehicle drives the motion of particles around the vehicle until they hit the surface or are ingested into an intake or other opening. Many critical safety, performance and quality features of the vehicle are determined by how the air flow manages these particles.
Road Sprays: For solid particles like dirt and rocks, the impact of these particles on the vehicle must be managed to avoid damage to the vehicle finish and components, while keeping passenger glass, exterior mirrors, exterior cameras and lights all as clear of material as possible. The regions around the wheels are designed to control the path of road spray water droplets carrying dirt, to reduce dirt deposition in critical areas on the vehicle body.
Wheels and Brakes: For the wheels and brakes, the brake disk surfaces should be kept clear of dirt and water. In addition, tiny brake dust particles are created during use of the brakes, and can create unsightly deposition patterns on the wheel rims. To alleviate these problems, wheel rim shape, splash shields and air flow guides may be used to help control particle deposition.
Snow Accumulation: The accumulation of snow particles while driving in snow conditions is determined to a large degree by the vehicle aerodynamics. Flow disruptions like small separations may allow particles to accumulate in certain regions which can then block air intakes, block visibility of the glass or exterior mirrors, cover vehicle exterior lamps, or affect windshield-wiper performance. The vehicle shape can be adjusted to smooth these flow disruptions and discourage snow accumulation.
Engine Bay Particle Ingestion and Soiling: The water and dirt kicked up by the vehicle wheels and other vehicles on the road, as well as water, snow and dust in the air can degrade performance of the engine and under-hood systems. In particular, air intakes are designed to breathe in clean air, and to minimize the pressure losses associated with filtering or separating particles from the incoming flow. Similarly, particle deposition can affect the performance of moving parts in the engine bay such as belts and fans. Air flow management for controlling particle deposition and ingestion affects the design of the grille, underbody, engine bay components, and component layout.
The vehicle aerodynamic and aero-acoustic performance are considered simultaneously with water management when considering the shape of the A-pillar, side mirror and other aspects of the vehicle shape. Performance related to management of water, dirt, snow, brake dust and other foreign particles is dependent on the small details of the vehicle surface and component design, which require fully-detailed prototypes for evaluation which are only available at the end of the design process. Fixing problems at this stage of design is very costly in terms of engineering effort, retooling, and addition of parts and expense to the vehicle. Information is needed earlier in the design process about the primary performance drivers for particle management such as exterior surface shape and engine-bay layout. Effects of detailed component design such as rain gutters and air intakes need to be understood before fully-detailed physical prototypes are available, so the vehicle can be designed to meet performance and safety targets.
Aerodynamic simulations can provide these insights, but are also challenging. Geometry details are needed that affect particle flows in the air and on the surface. Particles flows are also very sensitive to transient, turbulent flow effects, and accurate simulation of the air flow and particle trajectories is required.
Exa provides the solutions for simulation of aerodynamics and particle flows for assessing vehicle design goals. Air flow simulations are performed using Exa PowerFLOW. Using the air flow results, Exa PowerVIZ is used to dynamically release particles into the air flow and compute the particle trajectories until impingement on the surface. Particle hit-points and density are recorded for accumulation analysis. Further, surface properties can be defined so that particles can reflect off of surfaces and create complex flow paths through the engine bay or on the vehicle surface. In the particle simulation, particles can also be realistically captured as they flow through screens or heat exchangers. Overall, this capability allows investigation of a wide range of soiling and water management phenomena.