| People are not satisfied with the noise level of existing air-conditioner, and this problem has caught wide attention increasingly. The flow characteristics of indoor unit duct system have important influence on the noise level of indoor environment. Through the relationship study of indoor unit duct system between structure parameters and flow field characteristics, we can provide theory basis for the optimal design of indoor unit air duct, improve air flow and heat transfer performance and reduce noise levels.In this paper, based on the theory of Computational Fluid Mechanics and Aeroacoustics, we used Fluent software to establish the three-dimensional physical model of indoor unit duct system. Then we conducted a series of analysis about the tube heat exchanger and cross flow fan structure and parameters of indoor unit respectively to study the flow field and noise.My research includes the following contents:(1) Using Fluent software, combined with FW-H noise model, I summarized up a set of process about how to analyze the flow field and noise field completely. Firstly, we get the pressure data by numerical simulation, then combined with Fast Fourier Transform and Curel Equation to get the noise spectrum.(2) we used oval tube heat exchanger to replace circular tube heat exchanger, and researched how the heat exchanger structure can influence the aerodynamic performance and flow field of indoor unit. The results show that under any condition of air side flow status, the oval tubes fin have better heat exchange efficiency than that of the circular tube; Using oval tube fin heat exchanger can reduce the flow resistance of air duct system, improve the air volume, and the ratio of the length of axis of 2 oval tube works best. Compared with the circular tube, the calculation frequency range between 0 Hz to 1400 Hz, using oval tube can reduce the maximum sound pressure level 3 ~ 4 dB, reduce the minimum sound pressure level 4.5 dB, and has better effect in reducing low-frequency noise; Two kinds of oval tube, the oval tube a/b= 2 has better noise reduction effect, can reduce noise about 4 dB.(3) The structure of heat exchanger has a little influence on the location of the unsteady eccentric vortex of cross flow fan, and the greater the air volume, the greater the eccentric vortex. The pressure in the outlet volute tongue is biggest. The changes in the structure of heat exchanger mainly affect the air inside the heat exchanger fin in turbulent flow condition and the air into state of cross flow fan for the first time.(4) Cross flow fan with leaf blade trailing edge serrated, to some extent, can improve air flow and reduce noise; When the fan speed is very high, the role of to reduce the noise is not significant. Serrated blade can reduce noise caused by cross flow fan, but also cause air volume loss at the same time. Therefore in the practical when using this technology, it should be considered the balance between air volume and noise problem. |
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