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A numerical investigation of automobile sunroof buffeting on a prototype sport utility vehicle (SUV) is presented, including experimental validation. Buffeting is an unpleasant low frequency booming caused by flow-excited Helmholtz resonance of the interior cabin. Accurate prediction of this phenomenon requires accounting for the bi-directional coupling between the transient shear layer aerodynamics (vortex shedding) and the acoustic response of the cabin. Numerical simulations were performed using the PowerFLOW code, a CFD/CAA software package from Exa Corporation based on the Lattice Boltzmann Method (LBM). The well established LBM approach provides the time-dependent solution to the compressible Navier-Stokes equations, and directly captures both turbulent and acoustic pressure fluctuations over a wide range of scales given adequate computational grid resolution.

This paper presents an innovative automobile application of Computational Fluid Dynamics (CFD) as a complement to wind tunnel experimentation for the evaluation of rain water and wiper wash flow on the exterior of a moving vehicle. In addition to calculating the air flow around a car, a multi-phase CFD code was used to simulate rain drops in the air stream, rain drops impinging on the vehicle, and the transport of the “thin liquid film” of water on the vehicle surfaces. Time-dependent results for the location, velocity, and height of the water film on the windshield, A-pillar, and side glass were obtained. The CFD results compared favorably with a wind tunnel procedure. The variation of the calculated water film corresponded with observed patterns of water streaks on test vehicles. Design iterations performed on the computational model also agreed with similar test configurations.

The results of an experimental investigation of the flow in the near wake of a generic Sport Utility Vehicle (SUV) model are presented. The main goals of the study are to gain a better understanding of the external aerodynamics of SUVs, and to obtain a comprehensive experimental database that can be used as a benchmark to validate math-based CFD simulations for external aerodynamics. Data obtained in this study include the instantaneous and mean pressures, as well as mean velocities and turbulent quantities at various locations in the near wake. Mean pressure coefficients on the base of the SUV model vary from −0.23 to −0.1. The spectrum of the pressure coefficient fluctuation at the base of the model has a weak peak at a Strouhal number of 0.07. PIV measurements show a complex three-dimensional recirculation region behind the model of length approximately 1.2 times the width of the model.

Free expansion of straight tubes is the simplest test to evaluate tube properties for hydroforming applications and to provide basic understanding of the mechanics of tube hydroforming. A circular cylindrical tube is sealed at both ends and fluid, usually water, is pumped into the tube to increase its internal pressure to bulge and burst the tube. Previous numerical simulations of the free expansion tube test were limited to modeling the midsection of the tube under various assumptions of deformation path. The simulation results obtained deviated from the experimental results under all simulation conditions considered. A new model is developed in this paper in which the whole tube is simulated instead of considering only its mid-section. Judged by the pressure-expansion relations, the model accurately predicted free expansion hydroforming tests results.

Glass run-channel seals are located between DIW (Door in White) and window glass. They are designed to allow window glass to move smoothly while other two major requirements are met; (1) Provide insulation to water leakage and noise, and (2) Stabilize the window glass during glass movement, door slamming and vehicle operation. For a robust glass guidance system, it is critical to minimize the variation of seal compression force. In addition, it is desired to maintain a low seal compression force, which meets the minimum requirement for insulating water leakage/noise and stabilizing the window glass, for enhancing the durability of glass guidance system. In this paper, a robust synthesis and design concepts on the glass run-channel seal is presented. The developed concept is demonstrated with test data.

Copolymer materials have been used for the collection of vehicle exhaust gas samples since the inception of regulatory standards. Some of these copolymers contain N,N-dimethylacetamide (DMA), which is added to improve the physical properties of the copolymer and eliminate manufacturing problems. DMA is highly soluble in water, and in effect is rinsed from the emission bag surface by humid exhaust gas samples. This study shows that DMA can thus incorrectly add to test vehicle overall hydrocarbon emissions. The DMA contribution can be significant for lower level emission vehicles. This study introduces a new bag material, KYNAR®, which significantly reduces this interference.