Amulti-year, multi-vehicle study was conducted to quantify the aerodynamic drag changes associated with drag reduction technologies for light-duty vehicles. Various technologies were evaluated through fullscale testing in a large low-blockage closed-circuit wind tunnel equipped with a rolling road, wheel rollers, boundary-layer suction and a system to generate roadrepresentative turbulent winds. The technologies investigated include active grille shutters, production and custom underbody treatments, air dams, wheel curtains, ride height control, side mirror removal and combinations of these. This paper focuses on mean surface-, wake-, and underbody-pressure measurements and their relation to aerodynamic drag. Surface pressures were measured at strategic locations on four sedans and two crossover SUVs. Wake total pressures were mapped using a rake of Pitot probes in two cross-flow planes at up to 0.4 vehicle lengths downstream of the same six vehicles in addition to a minivan and a pickup truck. A smaller rake was used to map underbody total pressures in one cross-flow plane downstream of the rear axle for three of these vehicles. The results link drag reduction due to various technologies with specific changes in vehicle surface, rear underbody and wake pressures, and provide a database for numerical studies. In particular, the results suggest that existing or idealized prototype technologies such as active grille shutters, sealing the external grille and ride height control reduce drag by redirecting incoming flow from the engine bay or underbody region to smoother surfaces above and around the vehicle. This mechanism can enhance the reduction in wheel drag due to reduced wheel exposure at lowered ride height. Sealing the external grille was found to redirect the flow more efficiently than closing the grille shutters, and resulted in greater drag reduction. Underbody treatments were also
In order to reduce green house gases, hydrogen fueled vehicles are expected to be commercialized in the near future. Hydrogen is nontoxic, but it is flammable. A relatively low ignition energy can ignite a hydrogen-air mixture when the concentration of hydrogen is within a flammable range. Therefore safety concerns related to possible leakage from hydrogen fueled vehicles need to be addressed. In this study, we focus on the distribution of the lower flammability limit (LFL) of a hydrogen cloud when hydrogen is released from a fuel cell vehicle. CFD techniques, using FLUENT, are applied to the simulation of hydrogen dispersion from a parked vehicle’s tailpipe. We analyzed several hydrogen release scenarios to investigate the hydrogen cloud formation, thermal effects and transient behaviors. We also simulated the effects of the inclination of the garage ceiling and forced ventilation on hydrogen dispersion. We found that the configuration of indoor space affects the hydrogen cloud formation in certain ways. The simulation results can be further applied to define the codes, standards and recommended safety practices related to possible hydrogen leakage and the risk of ignition.
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