Abstract
The Ahmed Model is a generic automotive bluff body with "backlight" region configurable through variable angles. Despite relatively simple geometry, the model is capable of replicating dominant flow structures pertinent to those generated about the C-pillar of a practical road car.
Basic effects on drag force of two models arranged in longitudinal convoy were analysed as a function of the interval between the models. Two different scales of Ahmed models (100% and 75% respectively) with "critical" geometry (30 backlight) were utilised. Analysis was performed using both experimental and computational methods. Inter-vehicle spacing was varied between 0.25L to 2L (where L is the 100% scale model´s length). All experiments were conducted in the RMIT University
Industrial Wind-Tunnel (IWT).
Similar trends on drag coefficients were observed on the measured (lead 75% scale) model in both EFD and CFD analysis. At extremely close spacing, significant increase of drag coefficient was observed for the rear (100% scale) model. The vortex interaction between the models was identified as a primary influence in the drag forces observed. In spite of more accurate prediction of drag coefficient trend by the current CFD turbulence model, it was found to over predict the base pressure drop which was concluded from the higher drag coefficient predictions when compared to
the experiments.
Keywords - Ahmed car model, Computational Fluid Dynamics (CFD), Drafting, Future Generation Intelligent Transport Systems (FGITS), EFD.