Finite Element Analysis And Dynamic Characteristic Optimization Of The Stalk Impeller Based On Fluid-Solid Coupling

Stalk rubbing machine developed by China is a new kind of forage processing equipment between straw cutter and grinder. It was mainly composed of rubbing device and impeller blower, after rubbed by the rubbing device, the stalk was thrown out by impeller blower. In the working process of throwing material, the impeller will vibrate violently under the combined effect of gravity, centrifugal force and pressure generated by high speed gas-solid two-phase flow. Therefore the static and dynamic performance of impeller is directly influence the working performance of the whole impeller blower.In order to ensure the safe, reliable and stable operation of the impeller blower. Based on the simulation of the gas-solid two-phase flow field in the impeller blower of 9R-40 rubbing machine, the finite element analysis was carried out by using the unidirectional fluid solid coupling method in the study of impeller. The distribution of stress and strain of the impeller under the combined effect of two phase flow pressure, centrifugal force and gravity were obtained. Based on the finite element model, the free mode simulation of the impeller was carried out. Meanwhile, using the laser vibrometer technology measured the free modal frequency and vibration mode of impeller, the theoretical analysis and numerical calculation were verified by modal test. In addition, the gas-solid-solid coupling method was adopted to do the pre-stressed modal analysis in order to consider the influence of centrifugal force and gas-solid two-phase flow pressure on the intrinsic attribute of the impeller. Finally, The effects of different parameters on stress,strain and vibration modes of impeller were compared and analyzed, and the structural parameters(blade thickness, disc radius and disc thickness) affecting the vibration characteristics of impeller were optimized by using the Response Surface Methodology(RSM).Research results showed that:(1) When the impeller blower was throwing the rubbed stalk, the maximum equivalent stress of the impeller is 48.98 MPa, which occurs at the outer edge of the blade connected with the reinforcing plate and the disc, the change trend of stress and strain are the same.The maximum deformation of the impeller is 0.046 mm, which appears on the outer edge of the blade, there is a tendency that all the blades expanded to outward with the trend of tangential bending. After verification, the strength and stiffness of impeller meet the requirements.(2) The maximum stress, strain and total deformation of the impeller are less affected by the blade thickness. The maximum equivalent stress and the strain of impeller reduced with the increase of blade length. The maximum equivalent stress, strain and deformation increased with the increase of the impeller speed. The stiffener can reduce the equivalent stress, strain and total deformation of the impeller. The distribution of stress and strain ofimpeller does not change with blade length, blade thickness, rotational speed and the stiffener.(3) The relative maximum error of simulated and experimental modal frequency was3.99%. Moreover, the vibration modes and the position of the maximum amplitude were basically same. Thus it can be seen that the numerical calculation results were accurate.(4) The pre-stress increased the different-order natural frequency of the impeller, the first and the 2nd order frequencies increased obviously.(5) The resonance analysis showed that when the impeller blower was throwing the rubbed stalk the deviation between the first order pre-stressed frequency and the excited fundamental frequency meet the requirement. But the 2nd and the third order pre-stressed frequencies were close to the 2nd and the third order excited frequencies respectively. In order to improve the dynamic characteristics of the impeller, it is necessary to optimize the it.(6) The disc thickness had the greatest influence on the low-order pre-stressed modal frequencies. The blade thickness took the second place and the final one was the disc radius. After optimized, the deviation between the exciting frequency and the first order natural frequency increased from 21.98% to 35.82%. The deviation between the exciting frequency and the second order natural frequency increased from 8.76% to 11.11%. The deviation between the exciting frequency and the third order natural frequency increased from 4.27% to 7.55%. The total mass of impeller was reduced by 0.31 Kg. After optimization, the strength and stiffness of impeller can meet the requirements of working conditions, and the whole optimization result was feasible and effective.