The CFD Analysis Of Automobile Passenger Compartment Noise Influenced By Air Duct

Under the new situation of energy saving and emission reduction,new energy vehicles are more in line with the industrial development planning of the new era than traditional vehicles.Therefore,the development situation of the new energy vehicle industry at home and abroad is getting better and better,which also makes more people pay attention to the comfort of new energy vehicles in recent years.Noise is an important factor affecting the comfort of the car interior,and the improvement of the sealing performance of the car body makes the noise outside the car more difficult to enter the car interior,so the noise inside the car has become the key to the noise inside the passenger compartment.Since the air duct outlet of the automobile HVAC system is directly connected with the passenger compartment,the noise generated by high-speed fluid in the HVAC system pipe will directly enter the vehicle driving and passenger compartment,so it is of great significance to study the aerodynamic noise generated by the air duct of the automobile air conditioner to improve the comfort level in the passenger compartment of new energy vehicles.In this paper,based on computational fluid dynamics(CFD),numerical simulation method is used to analyze the characteristics of flow field and sound field in the passenger compartment of a new energy light truck under the influence of defrosting duct and blowing air duct of HVAC system.The main research contents of this paper are as follows:Firstly,the numerical simulation model and simulation method of air duct and passenger compartment are analyzed and determined.By comparing and analyzing the application range and advantages and disadvantages of each numerical simulation model in computational fluid dynamics software,combined with the research object of this paper,as well as defrosting conditions and blowing conditions,the simulation method of RANS was determined to add Realizable k-epsilon turbulence model in steady-state simulation analysis of flow field.The wide band noise source model is used to estimate the wind pipe noise source.In the transient simulation analysis,DES method was used with SST k-omega turbulence model,and the FW-H model was used to calculate the far field of the noise in the passenger compartment considering all the components of the noise source.Then,the characteristics of flow field and sound field in air duct and passenger compartment under defrosting condition are studied by using the determined model and method,and the rules are revealed.The geometric model and simulation model of defrosting air duct and the passenger compartment were established.Under the condition of meeting the defrosting performance of automobile windshield glass,the defrosting air duct inlet flow test value of 201.00 m~3/h and 380.00 m~3/h were used as the model input to explore the characteristics of air duct flow field and steady state sound field.The results show that,The distribution of air velocity field,gas pressure field and turbulent kinetic energy field in the air duct is related to the structure of the air duct and positively related to the inlet flow size.The noise values of air duct flow sources near the outlet of the near field air duct and near the seat in the far field passenger compartment were calculated by acoustic analogy method,the results show that sound pressure level are greatly influenced by duct along the block,and is not only related to monitoring position,also positively related to the size of inlet flow,maximum defrosting conditions when driving personnel ear noise maximum is less than the noise standard limit value,indicating that the defrosting duct can meet the noise performance requirements under the condition of meeting the defrosting performance.Meanwhile,the characteristics of flow field and sound field in air duct and passenger compartment of a new energy light truck were studied.With the maximum inlet flow of 450.00m~3/h as the input under the condition of satisfying the comfort of the passenger compartment,the calculation results of analyzing the flow velocity field and pressure distribution inside the air duct on the blowing surface and the noise source distribution on the surface of the air duct show that,that the noise source is mainly distributed at the sudden expansion and contraction of the duct structure.According to the FW-H noise source model,the sound pressure level near the human ear in the far field passenger compartment is up to 63 d B(A),and the noise value is too high,so there is room for optimization of noise in the passenger compartment.Finally,the structure of the blowing air duct is improved to solve the problems of unreasonable noise source distribution in the blowing air duct and excessive noise in the passenger compartment during the maximum inlet flow.According to the analysis of the internal gas flow velocity diagram and surface static pressure distribution diagram of the blowing face duct,the sudden expansion,sudden contraction and corner structure of the blowing face duct are found to be unreasonable,which leads to eddy current of the air flow,pressure pulsation,air flow regeneration noise and influence the noise in the passenger compartment.Therefore,combined with engineering practice,smooth transition processing was carried out on the structure of the sudden expansion and contraction of the duct,and the radius of the corner of the pipe was revised to R60.The steady noise source analysis of the improved air duct shows that the surface noise source of the air duct decreases.The comparison of sound pressure level of monitoring points in the passenger compartment before and after the improvement shows that the noise around the driver’s ear is reduced by 2d B,and the improvement effect is significant.Through the verification analysis of the air volume distribution of the blowing surface duct,the improved air volume distribution of the duct is still 2:3:3:2,which meets the requirements of the blowing surface.In this paper,the flow field and sound field in the occupant compartment of a car are studied by computer simulation method.The comfort of the vehicle is studied and improved before the formal production,which can reduce the physical model and physical test,thus effectively reducing the cost of product development and promoting the development of new products.