Proceedings of ICFD13: Thirteenth International Conference of Fluid Dynamics 21-22 December, 2018, Steigenberger Hotel El Tahrir, Cairo, EGYPT ICFD13-EG-6S15 Computational Study of the Overtaking Process of Road Vehicles with Proposed Techniques to Reduce the Interference Risk Ahmed Bahgat Mohamed Mechanical Eng., Faculty of Eng., Zagazig Univ., Egypt ahmedbahgat32@gamil.com Mohamed Ebrahim Edrees Electrical Eng., Faculty of Eng., Zagazig Univ., Egypt edrees888.me@gmail.com Ahmed Farouk AbdelGawad Mechanical Power Engineering Dept., Faculty of Engineering, Zagazig University, Egypt afaroukgb@gmail.com ABSTRACT This research is concerned with the computational investigation of the aerodynamic interference between road vehicles during the overtaking process. Four cases of vehicle interference were studied in open highways. Computational results covered pressure distributions around the interfering vehicles. Moreover, proposed techniques are presented to reduce interference risk. Thus, this paper may help in explaining many highway accidents by better understanding of the flow structure and changes of pressure distribution around the vehicles that depend mainly on the gap between the vehicles. KEYWORDS: Road vehicles, Highways, Vehicle interference, CFD 1. INTRODUCTION 1.1 General Background Safety of passengers is the principal consideration of this research. Typically, high-speed vehicles are exposed to big loads (forces and moments) in six degrees of freedom, which affect the vehicles performance and passengers’ safety. These loads can be clearly noticed in highways when two vehicles are moving very close to each other. This phenomenon is known as aerodynamic interference. In this case, there are additional loads (forces and moments) that affect the vehicles especially light ones; such as passenger cars, motorcycles, etc. These light vehicles are more exposed to drafting when overtaken by larger vehicles. For many years, several researchers investigated different cases of the interference of road vehicles. The aerodynamic behavior of the interfering vehicles during overtaking process and the changes of the drag force were studied by [1-7]. On the other hand, many attempts were carried out by many investigators to arrange and control the overtaking process and reduce driving risks [8-13]. However, there is still a plenty of research space to fully study and understand the endless cases of vehicles interference. 1.2 Theoretical Background As the vehicle moves through the air, there is an aerodynamic force that exists. The air resists the motion of the vehicle and the resistance force is called drag [1]. The coefficient of drag is a dimensionless quantity, which indicates a body's ability to generate fluid resistance, Eq. 1. Drag force (D) = 0.5 CD ρ v 2 A (1) Where, D is drag force, ρ is air density, v is velocity of the vehicle, A is the vehicle form area, and CD is the drag coefficient. Reynolds number is calculated as: Re = ρ v L/µ (2) Where, Re is Reynolds number, ρ is the air density, v is vehicle velocity, L is a characteristic length, and μ is the dynamic viscosity of air. 2. TYPES OF VEHICLES INTERFERENCE There are three types of vehicles interference, Fig. 1, that are explained in the following subsections. Fig. 1a Fig. 1b Fig. 1c Fig. 1. Types of vehicles interference.