Aeroacoustics Characteristics Analysis And Noise Reduction Of Ultra-high Speed Rolling Rotor Compressor

With the development and progress of society,noise pollution has been paid more and more attention.Due to the relatively low noise level,smooth operation,small vibration interference,simple and compact structure and other advantages,the application of Rolling Rotor Compressor in home air conditioning is more and more widely.However,with the increase of compressor rotation speed and people's requirements,the noise level of rolling rotor compressor is also becoming unacceptable.Aiming at the aerodynamic noise problem caused by high speed,the simulation prediction of noise radiation caused by flow-induced vibration and the theoretical modeling of the noise at the reed valve of the double-cylinder super-high speed rolling compressor were studied in this paper.The performance of the exhaust muffler under all working conditions was evaluated and improved by simulation.The main contents of this thesis are as follows:(1)Based on the Finite Element Method andBoundary Element Method,a multi-field simulation and prediction model of flow field,flow-induced vibration and noise radiation in compressor was established.It was concluded that the internal pressure of compressor varies sharply in a short time after the exhaust valve was opened,which is the main time of noise occurrence.The flow-induced vibration form was shown as the whole machine's axial translation at 360 Hz,the radiation of noise was isotropic in the radial direction and increases with the increase of the height in the axial direction.At 720 Hz,the noise radiation was almost isotropic in the radial direction,but in the axial direction,it was largest in the middle and decreases in both sides.(2)Constrained modal analysis of exhaust reed showed that the first,third,fourth and sixth modes of the reed were transverse bending vibration,the second mode was torsional vibration and the fifth mode was combined bending and torsion vibration,the higher mode was vibration combined bending and torsion.The first natural frequency of the reed was 261.80 Hz and the excitation frequency of the compressor system was 180 Hz,which indicated that there is no risk of resonance in the reed valve.(3)Based on the theory of mechanical vibration,hydrodynamics and acoustics,a theoretical model of the acoustic characteristics of the reed valve-muffler system was established through the theoretical analysis of forced vibration of the reed,refrigerant flow in the reed valve gap and sound propagation inside the muffler.It was found that the acoustic pressure at the muffler outlet within 1000 Hz was controlled by both the excitation frequency and the muffler transfer function,while it was mainly controlled by the impedance characteristics of the muffler after 1000 Hz.When the excitation frequency changes,the noise radiation at the muffler outlet was affected by both the excitation frequency and the transfer function of the muffler.Any dominant position of the two will cause the noise to increase,especially when the excitation frequency happens to be at the peak frequency of the transfer function,noise can be very loud.On the contrary,when the two factors work together,the noise energy will be dispersed at multiple frequencies and the total sound pressure will be reduced.The effects of reed width,thickness and system damping on the amplitude of reed and noise radiation at muffler outlet are similar.The purpose of noise reduction can be achieved by increasing the reed width,thickness and system damping,but at the same time,the amplitude of reed will also be reduced and affect its working characteristics.(4)The acoustic performance of exhaust muffler was analyzed and optimized by acoustic finite element method.It was found that the original muffler can only achieve ideal silencing effect at the second working condition,and it is difficult to meet the requirements at the first working condition.The influence of the outer diameter,length of the three chambers and the diameter of the connecting pipe on the transmission loss in the original muffler structure was studied,the results showed that the original structure can not guarantee a good silencing effect of 180 Hz under the whole working condition.The upper cavity was changed into a resonant cavity,by choosing appropriate parameters,the lower cavity has a peak noise attenuation at 180 Hz at the first working condition and the upper cavity has a peak noise attenuation at 180 Hz at the second working condition.The simulation results showed that this structure can ensure the good silencing effect of the muffler at 180 Hz at all working conditions.