Numerical simulation and experimental validation of radiation noise from vibrating shell of stalk impeller blower

Abstract: Stalk rubbing machine is a new type of forage processing equipment developed in China. It is mainly composed of rubbing device and impeller blower. When the stalk rubbing machine is working, the material is thrown out by the impeller blower after rubbed by the rubbing device. Its main problem is an increased level of vibration and noise of the impeller blower during the stalk rubbing machine running. However, the research of impeller blowers at home and abroad mainly focused on reducing the power consumption, increasing the throwing distance and throwing efficiency. There were few researches on reducing the vibration and noise of the impeller blowers. Because of the limitation of the experimental method, it was difficult to find out how the shell was excited by the pulsating gas-solid two-phase flow inside the impeller blower and how it produced vibration and radiated noise outwards. Aimed at these problems, the vibration radiated noise of the shell of the impeller blower was analyzed by the co-simulation method to predict the impeller blower's noise at the design stage of the stalk rubbing machine. Firstly, the ANSYS Fluent software was used to simulate the unsteady solid-gas two-phase turbulent flow in the impeller blower. Then the fluctuating pressure of the two-phase flow field was loaded into the inner surface of the shell. Secondly, the modal analysis and dynamic response analysis of the shell were carried out by using the finite element method which realized unidirectional coupling from gas-solid two-phase fluid to structure. With the vibration response of the shell as the acoustic boundary condition, the vibration radiation noise of the shell caused by unsteady flow was calculated by using the indirect boundary element method (IBEM) of the LMS Virtual Lab. Thirdly, Comparisons between the simulated values and the measured values of the vibration radiation noise of the shell were made, and the reliability of the numerical simulation was verified. Finally, the influence of shell thickness on the vibration radiation noise was analyzed based on the above co-simulation method. Research results showed that: 1) The fundamental frequency sound pressure levels for the simulation and experiment were basically the same. The changing trends of simulation results and the experimental results of the fundamental frequency and harmonics were also the same. Because the simplified simulation model made its stiffness smaller, the simulation results at the second and the third harmonic were slightly higher than the experimental results. Thus, it could be proved that the results of the co-simulation were credible. 2) The fundamental frequency sound pressure level was the highest. The second harmonic one came second, the third harmonic one was low, and the rest harmonic ones were very low and were neglected. 3) The sound pressure level of the radiated noise at the sides of the shell was the highest, particularly at inlet. And it was higher at outlet, too. 4) When the impeller rotational speed was 1 500 r/min, the best wall thickness was the combination of front and rear round shell thickness of 4 mm and the others' thickness of 3 mm. The research will provide the reference for further research on the noise of stalk rubbing machines and impeller blowers.