Research On Noise Distribution And Reduction Measures Of Counter-rotating Axial Fan

The counter-rotating structure of fan is two impellers rotate in reverse and guide each other.Because of its compact structure,high wind pressure,large flow rate and high efficiency,counter-rotating axial fan is widely used in coal mine.During the operation of counter-rotating axial fan,non-uniform flow is caused by two impellers,then results in large aerodynamic noise.In addition,the narrow space underground makes the working condition worse.It has a negative impact on both physical and mental health of staff,safe and efficient production,and energy consumption.Therefore,this paper took counter-rotating axial fan as research object,used sound test system and computational fluid dynamics method to carry out the test and simulation research on noise detection and reduction,which provides important measures for research of counter-rotating axial fan's noise.Firstly,introduced the structure and working principle of counter-rotating axial fan.Started from the internal flow state,explained the formation of aerodynamic noise.Took the variation of sound field under different operating conditions as research object,built noise test system by LMS Soundbrush,and the noise distribution of the fan at different speeds and different loading distance of conical flow controller was tested.The results show that the noise at second impeller was the highest,overall noise increased with the increase of rotating speeds.Overall noise of the fan decreased first and then increased with the decrease of the loading distance of conical flow controller.It has guiding for the research of noise source and sound field of fan.Secondly,a simplified three-dimensional model of the fan and impellers with different blade angle were established,then divided the grid.With the help of computational fluid dynamics software,the numerical simulation of the flow field and sound field inside the counter-rotating axial fan was carried out when the blade angle was changed respectively.The changes of the fan operating state were analyzed by steady simulation,unsteady simulation and noise simulation.The increase of two impellers' blade angle made total pressure of the fan increase,and the effect of first impeller's blade angle was larger than the second.To avoid high noise,the blade angle of first impeller should not change exceed 49°.The smaller first impeller's blade angle was,the smaller fan's sound pressure level was.Theoretical support was provided for the fan to change the blade angle to adjust the operating state.Finally,designed blades with holes,skewed blades and swept blades to solve the problem of excessive noise of counter-rotating axial fan.Used computational fluid dynamics method to analyze the aerodynamic performance and noise characteristics of different blades.When there were holes in blades,the overall noise of the fan was reduced,which made the total pressure of the fan decrease,the rotating noise caused by the interaction of impellers was decreased,but the total pressure decreased,too.Swept forward blades used in first impeller was the best,it can not only increase the total pressure of the fan,but also reduce the overall noise.It is instructive to reduce the noise of the counter-rotating axial fan by optimizing the blade structure.