Numerical Research On Wheel Spray And Related Body Soiling

Numerical Research on Wheel Spray and Related Body SoilingAutomobiles are entering people’s life increasingly and become necessities today. They are expected to be more than a kind of transportation and generally a clean surface away from the contamination of muddy water and dust is required especially for some cars with camera systems fitted in the surface and buses with body advertising. However, when an automobile travels on wet or muddy road the surface of the body will be exposed to wheel splash and spray. Hence, the research on the formation of body soiling and the exploration of measures to reduce body soiling are of great importance.Generally, approaches to study wheel spray and related body soiling are divided into theoretical studies, experimental studies and numerical simulation studies. Different from studies based on theories or experiments, with numerical simulation methods the phenomena and results of contamination can be obtained rapidly and some special conditions not available in experimental studies can be implemented easily. Besides, with numerical simulation results the spatial distributions of pressure and velocity as well as the trajectories of droplets can be visualized directly, which then can be used to analyze the structure of the flow field and the mechanism of the contamination.In this paper, a single rotating wheel model and a simplified Land Rover Discovery3model are used firstly to explore numerical simulation methods for wheel spray and body soiling respectively. Unsteady SST k-co model, DPM and Eulerian wall films model are selected for turbulence modeling, droplet trajectory tracking and water accumulating and moving on body surface respectively. Additionally, with experimental data and numerical results in early publications, the simulation results in this paper are validated, which pave the way for later simulations in this paper.Since the simulation scheme is determined, a modified square-back MIRA model is then selected and the discussion of wheel spray and body soiling will be based on this model with simple geometric features. The trajectories of droplets and the soiling pattern are achieved after numerical simulation. For a better analysis and evaluation, the surface of the modified square-back MIRA model is divided into several regions while Rc (Ratio of Contamination) is defined as a quantitative index for measuring the amount of contamination in a certain region. The quantitative results reveal that the regions corresponding to the side doors and tail lights are contaminated most, while the regions corresponding to the side windows are contaminated least. According to the simulation result, the process of wheel spray and related body soiling is divided into some sub-processes including motion of droplets in the wheel houses, transport of droplets in high speed uniform flow, change of the droplets movement where the flow separates, motion of droplets in wake flow and motion of films on body surface. Analyses are conducted and the relationship between the motion of droplets, the motion of films and automobile external flow field is obtained.The trajectories of droplets in the automobile external flow field are closely related to the motion of air. In this paper, four improvement measures are adopted based on the modified square-back MIRA model according to the relationship between droplets motions and flow structure. The four measures are adding wheel house shields, deflector on the rear edge of the roof, spoiler on the bottom of the tail and deflectors on both sides of the back surface, which are used to change the trajectories of the droplets by changing the flow structure, and the target of reducing body surface soiling is achieved. At last the reason of the improvement is discussed.In this paper, a numerical method based on FVM, integrating unsteady SST k-co turbulence model, DPM and Eulerian wall films model, used for wheel spray and related body soiling simulation is introduced and the effect of automobile external flow field on wheel spray and body soiling is analyzed and revealed. Four improvement measures for reducing body soiling are proposed based on automotive aerodynamics. All the works contribute to the study of automobile external water management and simulation of body soiling, provide guidance for low surface contamination design in the development of new cars, and lay the foundation for further research on accessories for body surface soiling reduction.