Overset Mesh-Based Computational Investigations on the Aerodynamics of a Generic Car Model in Proximity to a Side-Wall
ISSN: 1946-3995, e-ISSN: 1946-4002
Published October 21, 2019 by SAE International in United States
Citation: Bounds, C., Mallapragada, S., and Uddin, M., "Overset Mesh-Based Computational Investigations on the Aerodynamics of a Generic Car Model in Proximity to a Side-Wall," SAE Int. J. Passeng. Cars - Mech. Syst. 12(3):211-223, 2019, https://doi.org/10.4271/06-12-03-0015.
This article discusses an approach to simulating a generic idealized car model (Ahmed body) moving in close proximity to a side-wall, using a transient Computational Fluid Dynamics (CFD) method. This phenomenon is very important in motorsports, where racing close to the safety barrier is common. Driving in close proximity to a side-wall alters the aerodynamic characteristics of the vehicle significantly; however, only a handful of published works exist in this area. Additionally, the experimental studies conducted in the past suffer from certain inadequacies, especially in terms of simulating the side-wall. This casts some uncertainty as to the relevance of these studies to the real-world problem. The present study attempts to imitate the real-world flow phenomenon by taking a nontraditional CFD approach of translating the body relative to the stationary surrounding fluid and side-wall instead of the classical method of flowing air over a stationary vehicle model. This was achieved by using a relatively new and computationally efficient meshing technique for overlapping grids called the “Overset” or “Chimera” mesh. The initial task was to accurately predict the flow over the rear slant of the 25° slant angle Ahmed body model, where previous studies struggled to achieve accurate enough predictions using the eddy-viscosity turbulence models. In the present study, Menter’s Shear Stress Transport (SST) turbulence model, with modified closure coefficients, is utilized to accurately predict the flow characteristics in the initial separated shear layer and flow reattachment over the rear slant. Compared to the eddy-viscosity CFD simulations of an isolated 25° slant angle Ahmed body, as seen in the existing literature, the results presented in this article show significantly better correlations with the experimental results in terms of overall aerodynamic characteristics. The wall proximity studies show a strong influence of the presence of the wall on the overall aerodynamic characteristics of the vehicle body. When compared with the experimental studies, although both show similar trends, there exist significant differences between the experimental and CFD-predicted results, which tend to worsen as the body approaches the wall. These differences can be attributed to the fact that the CFD simulation of the flow around the side-wall is more realistic compared to the experimental implementation.