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Technical Paper

Hybrid Technique for Underbody Noise Transmission of Wind Noise

Wind noise has become an important indicator for passenger automobile quality. Several transmission paths can be related to different parts of the vehicle exterior. While the greenhouse (side glasses, windshield, seals & others) often dominates the interior noise level above 500 Hz, the contribution coming from the underbody area usually dominates the interior noise spectrum at lower frequencies. This paper describes a framework of numerical tools which is capable of determining realistic underbody turbulent and acoustic loads being generated for typical driving conditions, as well as performing the noise transmission through underbody panels and the propagation of sound to the drivers ear location.
Journal Article

A Computational Process for Early Stage Assessment of Automotive Buffeting and Wind Noise

A computational process for early stage vehicle shape assessment for automotive front window buffeting and greenhouse wind noise is presented. It is a challenging problem in an experimental process as the vehicle geometry is not always finalized. For example, the buffeting behavior typically worsens during the vehicle development process as the vehicle gets tighter, leading to expensive late counter measures. We present a solution using previously validated CFD/CAA software based on the Lattice Boltzmann Method (LBM). A CAD model with realistic automotive geometry was chosen to simultaneously study the potential of different side mirror geometries to influence the front window buffeting and greenhouse wind noise phenomena. A glass mounted mirror and a door mounted mirror were used for this comparative study. Interior noise is investigated for the two phenomena studied. The unsteady flow is visualized and changes in the buffeting and wind noise behavior are explored.
Technical Paper

Design and CFD Analysis of an NHRA Funny Car Body

This paper describes the methodology used to design and perform a CFD analysis of a Chevrolet Impala SS Funny Car body. This body was designed for the purpose of making it available for teams to race it in the National Hot Rod Association (NHRA) drag racing series beginning with the 2007 race season. Several challenges were presented in this project: (1) This was the first time a General Motors drag racing body for use in professional classes (Funny Car or otherwise) was ever designed in CAD. (2) The body was originally designed as a 2007 Chevrolet Monte Carlo. After the tooling was completed, changes in Chevrolet’s product lineup required that the body be changed to a 2007 Impala SS. (3) Budget constraints precluded CFD analysis until after the bodies were already being manufactured. There were several teams that raced the new body during the 2007 race season. One of these teams won the Funny Car Driver’s Championship.
Journal Article

Response of a Prototype Truck Hood to Transient Aerodynamic Loading

A study was performed to determine the fluid structure interaction (FSI) for a prototype truck hood for transient aerodynamic loads. The growing need to make vehicle panels lighter to enhance the fuel economy of vehicles has made hood panels more prone to deformation and vibration from aerodynamic loads. Moreover, as global pedestrian crash standards become more stringent to provide safer front end designs to minimize injuries to head and leg, automotive manufacturers are being required to design flexible hoods that crush significantly more than the present designs to absorb the crash energy better. These flexible designs lead to potentially undesirable deformations and/or vibration behavior of the hood at typical highway speeds.
Journal Article

Assessment of Broadband Noise Generated by a Vehicle Sunroof at Different Flow Conditions using a Digital Wind Tunnel

Abstract For the automotive industry, the quality and level of the wind noise contribution has a growing importance and therefore should be addressed as early as possible in the development process. Each component of the vehicle is designed to meet its individual noise target to ensure the wind noise passenger comfort level inside the vehicle is met. Sunroof broadband noise is generated by the turbulent flow developed over the roof opening. A strong shear layer and vortices impacting on the trailing edge of the sunroof are typical mechanisms related to the noise production. Sunroof designs are tested to meet broadband noise targets. Experimentally testing designs and making changes to meet these design targets typically involves high cost prototypes, expensive wind tunnel sessions and potentially late design changes.
Technical Paper

Advances in Modelling A-Pillar Water Overflow

Abstract Driving when it is raining can be a stressful experience. Having a clear unobstructed view of the vehicles and road around you under these conditions is especially important. Heavy rain conditions can however overwhelm water management devices resulting in water rivulets flowing over the vehicle's side glass. These rivulets can significantly impair the driver's ability to see the door mirror, and laterally onto junctions. Designing water management features for vehicles is a challenging venture as testing is not normally possible until late in the design phase. Additionally traditional water management features such as grooves and channels have both undesirable design and wind noise implications. Having the ability to detect water management issues such as A-pillar overflow earlier in the design cycle is desirable to minimize the negative impact of water management features. Numerical simulation of windscreen water management is desirable for this reason.
Journal Article

A Computational Approach to Assess Buffeting and Broadband Noise Generated by a Vehicle Sunroof

Abstract Car manufacturers put large efforts into reducing wind noise to improve the comfort level of their cars. Each component of the vehicle is designed to meet its individual noise target to ensure the wind noise passenger comfort level inside the vehicle is met. Sunroof designs are tested to meet low-frequency buffeting (also known as boom) targets and broadband noise targets for the fully open sunroof with deflector and for the sunroof in vent position. Experimentally testing designs and making changes to meet these design targets typically involves high cost prototypes, expensive wind tunnel sessions, and potentially late design changes. To reduce the associated costs as well as development times, there is strong motivation for the use of a reliable numerical prediction capability early in the vehicle design process.
Technical Paper

Update on A-Pillar Overflow Simulation

Side glass soiling due to A-Pillar overflow is a growing challenge for automotive manufacturers. Pressure to remove traditional vehicle features, such as A-Pillar steps, to achieve lower drag targets has meant that A-Pillar overflow has become more common. A-Pillar overflow, however, can be a major concern if important regions of the side glass are affected. The ability to predict where and under which conditions the A-Pillar will overflow is important for making correct design decisions. The development of a numerical simulation solution is desirable as experimental testing requires a late stage prototype, making it very difficult and costly to correct problems. This paper provides an update on the ability of simulation to predict A-Pillar overflow, comparing simulation and numerical results on a test vehicle. These results include both with and without wipers, as the presence of wipers was found to impact the A-Pillar overflow in the experiments.