| As urbanization is accelerated, construction machinery is used more and more widely, and its noise performance gradually become the focus of attention. In its noise components, aerodynamic noise occupy a certain proportion. With the development of vehicle engineering and technology, the engine intake and exhaust noise has been effectively controlled and gradually reduced, and aerodynamic noise caused by engine cooling fan increasingly prominent. In general, the construction machinery's tasks are heavy, and large engine power is needed; what's more, construction machinery rarely moves with high speed, which lead to a poor engine cooling conditions. Thus a large flow fan is needed for cooling, and therefore large fan noise is generated compared to other vehicles. In this paper, based on Lighthill's acoustic analogy theory, the Infinite Element Method(IFEM) combined with the computational fluid Dynamics(CFD) was utilized to calculate aerodynamic noise caused by the cooling fan in a small excavator, and several solutions was searched to reduce the fan noise. The main research word and conclusion were divided into following areas:First, the original power component's flow and sound field are simulated, using the CFD software Fluent to simulate the flow field with three different gas model(constant gas model/ ideal gas model/ incompressible ideal gas model), then using Actran to simulate the sound field according to different flow field results. The result indicates that using incompressible model is more accurate, and it can save much time compared with ideal gas model.Secondly, starting from the noise source and the propagation path, the noise reduction of aerodynamic noise is studied.It contains:(1) Different fan's effect on thermal management and aerodynamic noise. The original fan with eight constant chord blades were replaced by a fan with unequal spaced blades and a fan with ten forward curved blades. It is found that the fan with unequal spaced blades generates more peak points on the noise spectrum, which makes the noise level higher; the fan with ten forward curved blades reduce the noise level.(2) Make some small changes on the opening-hole program on power component. The simulation finds that effects of openings on the flow field of a lot of the hole is too much noise came a greater amount of computation; Too less opening hole makes eddy current increase and the cavity resonance enhance, which makes noise increases. Compared different program's far-field noise value and flows through the radiators, the original program is better.(3) Put sound absorbing material-- polyurethane foam on the wall of power component; Simulation shows that it can reduce the far field noise is obviously.Then, the influence of Physical property parameters for sound transmission loss of bulkhead is analyzed. Power Cabin is a closed space surrounded by thin plates. Bulkhead's sound insulation performance have a great impact on the noise transmission. Using noise analysis software Actran, analyze the impact of plate thickness and material parameters on insulation based on a 1m×0.5m board, and on this basis analyze the noise performance of the power compartment main board member and improvements. Basing on the result, sound insulation performance of main bulkheads of the power cabin is analyzed, and the way to improve the performance is found.In this paper, aimed at the aerodynamic noise of the cooling fan of the power cabin, the corresponding noise reduction scheme is simulated and analyzed from noise source and sound propagation, and a good result is obtained. Using computer to simulate and analyze aerodynamic noise of construction machinery plays a guiding role in the implementation of a concrete practicing scheme, and it has important significance to reduce unnecessary experimental process. |
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