Aero-acoustic Analysis Of A-level Automotive HVAC System

With the rapid improvement of living standard, consumers are eager to get more comfortable driving environment. However, vehicle noise becomes a disturbance to the passengers or drivers which becomes a research focus in recent years. Excessive noise not only affects the normal communication inside the vehicle, but also causes driver and passengers feel fatigue, and even affects driving safety, puts people and property safety in danger. Therefore, how to reduce the noise inside car became a concern in recent years. With the decrease of exterior noise, and the improvement of body tightness, aerodynamic noise of HVAC(heating, ventilation and air-conditioning) system becomes the main interior noise source. It is significant to improve the aerodynamic noise characteristics of HVAC system.Aero-acoustic of HVAC system includes fan aero-acoustic and ducts aero-acoustic. Fan structure parameters, such as blade shape, blade number, tongue gap and volute shape have been studied by many scholars, and fan aero-acoustic characteristics have been improved step by step. Duct structure was optimized to reduce the pressure drop inside duct, and duct aero-acoustic characteristics was improved accordingly. HVAC assembly was focused studied in this paper. Impact of the HVAC assembly structure on aero-acoustic characteristics was studied, and optimization was carried out to improve aero-acoustic characteristics.Main contents of the research are as followed:Air flow test and noise test of HVAC system were carried out, mass flow and noise level under different fan rotation rate was obtained accordingly. Fan order analysis and outlet noise spectrum of HVAC system were analyzed and compared, and simulation boundary conditions were obtained.By analyzing the basic theory of flow field and sound field, 3D modulus of HVAC system, turbulence model and acoustic model were established. Flow field simulation and sound field simulation were carried out, and simulation results were compared with experiment results, so the accuracy of the simulations was verified. Distribution of flow field and sound field were analyzed, and aero-acoustic characteristics of different noise sources were compared.According to the flow field and sound field analysis results, aero-acoustic characteristics of HVAC system were optimized. First of all, RSM was used to optimize aero-acoustic characteristics of HVAC system, two optimization mechanisms were used to make multi-objective optimization, and the mathematical functions were established among air flow, pressure drop, sound pressure level and angle of vent door, foot door, cold-warm door. The outlet aero-acoustic characteristics were improved without deteriorating flow field characteristics of HVAC system according to the mathematical functions, and two optimization results were basically in same. Comparing with multi-objective optimization method, HVAC structure was improved by adding baffle, outlet aero-acoustic was reduced a little. Finally, processes and results of three optimization program were comprehensive compared, to provide a guideline for design and optimization of HVAC system.