Research On Characteristics Of Aerodynamics And Wind-induced Vibration For A Road Vehicle By Fluid-structure Coupled Method

The environmental wind will generate aerodynamic force which has an important influence on the security, stability, comfort of High-Speed Vehicle. It is important to consider aerodynamic in the study about body designing, system dynamics and suspension designing. Currently, scientific researchs rarely consider the body vibration influence on the flow structure. This paper mainly reaserch domestic and international applications of fluid-structure coupled method(or fluid-structure interaction-FSI) on the plane, train and automobile and basic theory of fluid-structure interaction, computational fluid, structural analysis, vibration and so on. The purpose is to find out the best numerical simulation method which would be applied to the contents of thesis. When the accuracy of the numerical simulation results is verified by the wind tunnel test results, the numerical simulation program of the paper will be determined. Finally, the numerical simulation method is used in the engineering applications which are the vehicle vibration, choke plate vibration and time-varying crosswind causing sideslip and roll. Specific research contents are summarized as follows:First, the paper proposes the FSI method which is used in the numerical simulation of MIRA model to research the characteristics of aerodynamic and wind excitation. The method will couple the fluid and structural simulation which generally are separate calculation system. The wind tunnel experimental techniques(aerodynamic measurement technique, the displacement measurement technology, PSI pressure scanning technology, etc.) would verify the numerical simulation method. The deviation of the both methods is within ± 10%. The numerical simulation method has certain feasibility and effectiveness in the engineering practice, so it has a certain guiding significance. Through flow field structure analysis, the FSI phenomenon has a relatively strong influence on the aerodynamic lift, the impact mechanism is that the location change of the body or attachments will lead to the topology changes of the shedding vortex or separation vortex.Second, the paper researchs the vibration characteristic of vehicle and choke plate under different speed. The simulation results show that:(1) The FSI phenomenon has a relatively strong influence on the aerodynamic lift. When the speed increases, the wind-induced vibration effect also increases.(2) When we analyse the vehicle flow field, we find that aerodynamic lift difference rate is 38% at 140km/h, the NO-FSI results are relatively small. If the design of car is based on these results, the product design will be biased towards the adventure.(3) The wind excitation phenomenon could cause a vibration of the elastic choke plate, the phenomenon will not only affect the aerodynamic performance of the choke plate but also cause breaking of the choke plate.Third, the paper researchs three different time-varying crosswind(linear crosswind, pseudo step crosswind and sine crosswind). The simulation results show that:(1) The results of the FSI and NO-FSI have little difference, so linear crosswind relatively less affects on the aerodynamic.(2) The pseudo step crosswind will produce instantaneous dangerous working conditions. The conditions need the high level of vehicle stability and driver. When the car is in the high speed, it is very dangerous.(3) The FSI method and NO-FSI method have a large gap in aerodynamic lift. The NO-FSI method will make that the design bias towards the adventure. When the high speed car is running in the long time sine crosswind conditions, the risk will increase, the driver should avoid running in this condition for a long time at a high speed.In summary, the paper research the different between the FSI method and NO-FSI method based on the basic theory, numerical simulations, wind tunnel experiments. The traditional CFD prediction of the aerodynamic lift force is smaller than the actual situation, it will impact the prognosis of dangerous situations in the autopilot and suspension automatic adjust system. But the FSI numerical simulation more close to the actual situation, it will provide some more accurate reference datas for these intelligent systems.