Numberical Simulation Of Cars In The External Flow Field Based On Different Turbulence Models

With the improvement of people’s living standards and the development of industrial technologies, the car gradually becomes part of people’s travel. Changes in the aerodynamic characteristics have great impact on the car’s economy, stability and security. Therefore, the study of automotive aerodynamic changes has important significance. Currently, many scholars have carried out simulation study of a single car. However, there are no uniform standards for selecting the turbulence model in car simulation and most scholars select turbulence models based on their experience. Therefore, calculation results based on different turbulence models are also differentWith the Ahmed model as the object of study, this paper uses professional software GridPro to partition the grid and selects four turbulence models for car simulation. The simulation results are compared with the experiment values to work out an appropriate turbulence model for the car flow field. Then this paper simulates a simplified van by analyzing its flow characteristics. Based on this simulation, this paper recommends that an air deflector be added to the tail of the van to reduce the aerodynamic drag force. According to the driving conditions of cars, car exceeding and car crossing usually occur. This paper uses three turbulence models to simulate car crossing, compare the simulation results, and analyze the aerodynamic force changes of the car at different time.The calculation comes to the following conclusions:1. In Ahmed model simulation, seven different Ahmed models and four turbulence models are simulated. The simulation results are compared with the experimental values and then the Ahmed model with a25°angle is used to analyze the tail vortex. Results show that the SST model is suitable for the simulation of the flow field. The error is relatively small, with an average error of less than7%.2. Based on the van simulation, this paper recommends that an air deflector be added to the tail of the van. Adding an air deflector to the upper side of the van tail reduces the aerodynamic drag force. However, how much the aerodynamic drag force is reduced varies with the size of the air deflector. In this paper, the aerodynamic drag force decreases by8.3%when a short air deflector is used, by14.2%when a long air deflector is added to the upper side of the van tail, and by4.6%when a long air deflector is added to the downside of the van tail.3. In the simulation of car crossing, three turbulence models are used:standard k-εmodel, SST model, and RNG model. The calculation and comparison results show that the SST model is applicable to the simulation of car crossing. When the relative position is x/L=-1，negative pressure appears in the car between the sides. The side torque comparison and analysis show that the side torque increases10%during car crossing. This has a certain impact on the car stability.