Numerical Simulation Of Aerodynamic Drag Reduction For Van

In this thesis, in order to increase van tail pressure and reduce its pressure differential resistance, numerical simulations were carried for simple van models adding different additional devices using FLUENT software.Firstly,numerical simulation methods are introduced briefly, including the foundation of computational fluid mechanics, the steps of numerical simulation of, differential equation and FLUENT CFD software.In order to improve the reliability of the 3D numerical simulation, a standard simple van model is simulated, to study its external flow field characteristics and the generating mechanism of resistance. Standard k-εand RNG k-εturbulence model are applied to calculate the standard van model. Results from RNG k-εturbulence model are closer to the experimental value than those from standard k-εturbulence model. The RNG k-εturbulence model is successful and effective to simulate the flow fields of van. Then van body truck model with three horizontal and three vertical grid boards was simulated to analyze its flow characteristics and drag reduction mechanism. The numerical results were compared with existing experimental data and verified that the standard model and corresponding CFD method are reliable. Considering the actual situation of van, the standard model is simulated again in consideration of the ground effect. The results showed that negative pressure in the tail area and pressure resistance increased under ground effect. It provided contrasting data for the next numerical simulation.Using the same numerical simulation method, structural grid and boundary conditions, 3D numerical simulations are applied to the models adding different shapes and inclined stern plate and spiral baffle. Numerical results are compared with the standard model to study theirs external flow field characteristics and drag reduction mechanism.Numerical results show that the plates added at the rear have a good effect for delaying flow separation and raising the pressure in the wake. The initial separation from the trailing edge of the model is delayed, which subsequently reattaches on the added plates. The flow reattachment on the plates decelerates the outer flow which in turn increases the pressure significantly at the edge of the plates where the flow separates again to form a vortex in the wake. This significant rise in the pressure has a favorable effect on the pressure drag. Therefore, the pressure drag reduced evidently after installing the plates which extend from the bottom and the sides of the model. The added plates have the drag reduction effect when the deflection angle is in the range of 10~15°. Modifying the wing shape of the added plate from straight line into Witozinsky curve, a lower total drag is obtained. A reduction of the total drag coefficient by 11.98% when a curved additional plate is installed without ground effect. If the ground effect is considered, the maximum reduction of the total drag can be up to 13.31%.Numerical results show that adding suitable additional device can effectively reduce aerodynamic drag of van model. Installing the stern plate in vehicle's tail or installing the spiral baffles above and lateral of the vehicle achieve very good drag reduction effects. At the same time, these two kinds of drag reduction device are simple, low cost and convenient in installation, which can applied to van through perfecting.We use the numerical methed to study simple , feasible, low-cost devices to reduce efficiently the aerodynamic drag of van. The simulation and mechanism analysis of drag reduction can provide theoretical basis for the design of van.