Proceedings of the 25 th UKACM Conference on Computational Mechanics 12 13 April 2017, University of Birmingham Birmingham, United Kingdom Simulation of Aerodynamic Behaviour of a Road Vehicle in Turbulent Flow *Ahmed Al-Saadi, Ali Hassanpour, Yousef Ghaffari Motlagh, Tariq Mahmud School of Chemical and Process Engineering, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT *pmaash@leeds.ac.uk ABSTRACT This study concentrates on different aerodynamic drag reduction techniques to reduce the aerodynamic drag coefficient and increase the stability of a three-dimensional full-size road vehicle. There are many modern aerodynamic add-on devices and modifications which are used in this research. All of these aerodynamic devices and modifications are used individually or in combination. Optimization of mesh parameters is carried out by analysis of the mesh data. Unstructured tetrahedral cells are used throughout the global domain to cope with the geometrical complexity of the car model. Inflation layers with prismatic cells are used to provide an accurate estimation of the velocity profiles near the surfaces of the car. Computational Fluid Dynamics (CFD) analysis based on steady state Reynolds-Averaged Navier-Stokes (RANS) turbulence modelling is used. Realizable k - - models are considered in this study. Good agreement has been achieved between the calculated drag coefficient for the baseline models and the experimental data for all types of turbulence models. It is found that the use of some types of aerodynamic modifications and devices can reduce the aerodynamic drag coefficient and increases the car stability. Keywords: Simulation; Aerodynamics; Road Vehicle; Turbulent Flow. 1. Introduction A rise in fuel prices has led to increasing concern about fuel consumption especially for vehicles. A large part of the engine power is used to overcome the air resistance force and improvement of aerodynamic behaviour can lead to a decrease fuel consumption. Experimental tests and computational simulations have been performed to reduce the drag coefficient of road vehicles and to improve the aerodynamic behaviour. The simple geometry of wagon model was achieved with modifications of the front part by Guo et al. [2] using computational fluid dynamics analysis. The k- turbulence model was used to calculate the drag coefficient. The bottom part of the body was assumed as a flat surface. Some parts of car as wheels and rear view mirrors were neglected in modelling to simplify the simulation. This analysis was based on three different slantwise angles of the back windshield. Aljure et al. [1] studied four different LES models, the QR, the VMS, the SIGMA and the WALE, in the bluff bodies using relatively coarse grids. The SIGMA, QR and VMS models were used for the first time to resolve the flow around simplified vehicle models (the Ahmed and the Asmo models were used as baseline models). Three meshes were used with each car model. Number of nodes for the Asmo model was higher than the Ahmed model. Both cases of cars were simulated using the same boundary conditions. The Reynolds number of 7.68×10 5 based on the height of the body was used for both cases. It was found that coarse grids are useful in LES simulations. Khalighi et al. [3] evaluated Immersed Boundary (IB) and body-fitted methods. The IB method does not require mesh to be conformal to geometry and therefore will speed up the grid generation process. The aerodynamic behaviour of Chevy Tahoe 2006 was studied using the Reynolds-Averaged Navier Stokes solver. Then, velocity, surface pressure and drag coefficient measurements were used to check the simulation results. The drag coefficients for the IB and the body-fitted methods were within 3% and 3 7% of the experimental measurement, respectively. The drag coefficient of Sports Utility Vehicles (SUVs) is higher than saloon cars because the size and the rear part design of this kind of vehicles. However, the flow field analysis around SUVs is difficult