Numerical Prediction Of Vibratory Noise And Researches Of Noise Reduction For Centrifugal Fan

Centrifugal fan is widely used as a kind of universal fluid machinery and its high noise has already become one of the main noise sources that decrease the comfort when people working and living.Developing the vibratory noise prediction and the noise control technology research has great theoretical significance and engineering application value.The domestic and international research trend is analyzed systematically,and the vibration sources and noise sources are categorized.According to the typical centrifugal fan,the vibratory noise experiment is carried out in the semi-anechoic room and the vibration of the fan,the radiation noise of volute,the fluctuation force on the volute interior surface,the wind velocity in the pipe and the noise in the pipe are obtained.These data will be used to validate the fan fluid field simulation method and the vibratory noise perdition method.Simultaneously it will provide the contrast data for the verification of fan optimum design.The impeller model is acquired by the laser scan system.Considering the clearance between the impeller rear plate and volute and the bugle-like inlet,the fine structured grid of the whole field is meshed.The total fluid region includes the rotating zone containing the impeller with the ladder shape,volute zone and the round-square transition with the succedent region.The steady flow field is calculated by adopting the RANS method and the transient flow field is calculated by Large Eddy Simulation(LES)method.The validity of these methods are verified by comparing velocity with realistic result and the pressure fluctuation experiment result at three positions.So the method of predicting the fluid excitation source is obtained.The dynamic force and moment that the fluid excites on the impeller can be got by the LES method.According to the rotor dynamics,the dynamic force at the bear position can be got.By using the structure finite element method,the dynamic displacement caused by the bear dynamic force and the fluctuation force on the volute interior surface is predicted.After that,the volute structure noise radiation is predicted.So it syncretize the stead filed,unsteady field,structure finite element method,acoustic finite element method and develop the integral vibration and noise radiation prediction method of volute.Comparing with the experiment result in the semi-anechoic room,the effectiveness of the method is validated.Based on the fluctuation force on the impeller and on the volute interior surface,Adopting rotating dipole mode,using the acoustic finite method,the noise in the pipe which connected with the fan is predicted.The result is close to the experiment result,this prove that the method of predicting the noise radiated from the rotating impeller and the fluctuation force on the volute interior surface is very accurate and reliable.Lastly,the noise control methods are sorted out one by one.Focusing on the fan,according to the theoretical analysis and the vibratory noise measurement,methods such as pasting damping material,strengthening the support and modifying the shape of the blade are adopted.The experiment shows that the volute noise decreases by about 7dB at shaft frequency,the overall high frequency band declines by 4dB or so;the velocity in the pipe decreased by 0.5 m/s,the noise in the pipe decreases by about 3dB at the shaft frequency and about 4 dB at blade pass frequency.