2020/01/29 by Filipe Fabian Buscariolo, Buscariolo, Filipe F., Gustavo R. S. Assi +3
Engineering · Environmental Science · #Aerodynamics and Fluid Dynamics Research #FOS: Physical sciences #Fluid Dynamics (physics.flu-dyn) #Fluid Dynamics and Vibration Analysis #Wind and Air Flow Studies
paper · pdf · doi:10.48550/arxiv.2001.11074
openalex publication_date 2020/01/29 · openalex created_date 2022/07/26 · openalex updated_date 2026/07/28
The Ahmed body is one of the most studied 3D bluff bodies used for automotive\nresearch and was first proposed by Ahmed in 1984. The variation of the slant\nangle of the rear upper surface on this body generates different flow\nbehaviours, similar to a standard road vehicles. In this study we extend the\ngeometrical variation to evaluate the influence of a rear underbody diffuser\nwhich are commonly applied in high performance and race cars to improve\ndownforce. We perform parametric studies on the rear diffuser angle of two\nbaseline configurations of the Ahmed body: the first with a 0 degree upper\nslant angle and the second with a 25 degrees slant angle. We employ a\nhigh-fidelity CFD simulation based on the spectral/hp element discretisation\nthat combines classical mesh refinement with polynomial expansions in order to\nachieve both geometrical refinement and better accuracy. The diffuser length\nwas fixed to the same length of 222 mm similar to the top slant angle that have\npreviously been studies The diffuser angle was changed from 0 to 50 degrees in\nincrements of 10 degrees and an additional case considering the angle of 5\ndegrees. For the case of a 0 degree slant angle on the upper surface the peak\nvalues for drag and negative lift (downforce) coefficient were achieved with a\n30 degrees diffuser angle, where the flow is fully attached with two streamwise\nvortical structures, analogous to results obtained from Ahmed but with the body\nflipped upside down. For diffuser angles above 30 degrees, flow is fully\nseparated from the diffuser. The Ahmed body with 25 degrees slant angle and a\ndiffuser achieves a peak value for downforce at a 20 degrees diffuser angle,\nwhere the flow on the diffuser has two streamwise vortices combined with some\nflow separation. The peak drag value for this case is at 30 degrees diffuser\nangle, where the flow becomes fully separated.\n