Dynamic Characteristics Of Impeller Of Perturbed Six-bent-bladed Turbine Based On Fluid-structure Interaction

The pesudoplastic luid with shear thinning property is a kind of non-Newtonian fluid widely used in the industrial field.It is very important to study flow field structure and the coupling effect of impeller in the stirred tank for the homogeneous mixing and efficient mass transfer of pseudoplastic fluids.The existing analysis of the flow field and structure field is mostly based on the one-way coupling theory,while that can only reflect the effect of fluid on solid,which cannot reveal the influence of solid structure deformation on fluid.Therefore,based on bidirectional fluid-structure interaction method,the flow field structure and the modes of 6PBT impeller are analyzed,and the agitation characteristics and the reinforcement mixing mechanism of 6PBT impeller are investigated,which provides a theoretical reference for the optimization of the agitator.In the rheological test of pseudoplastic fluid(Xanthan gum solution),the relationship between the apparent viscosity and the shear strain rate of xanthan gum solution in transitional flow conformed to the Herschel-Bulkley rheological model.And the data obtained from the PIV experiment is consistent with the simulation results.Numerical simulation results of stirring flow field indicate that the 6PBT impeller's discharge direction is inclined upwards or downwards,which can generate an asymmetrical flow field structure,and can effectively eliminate the upper and lower isolation zones and make the fluid in the tank all go into chaos.The rheological behavior of pseudoplastic fluid has a great influence on the velocity distribution of the flow field,especially when the rheological index is greater than0.3,the rheological effect is more obvious.Increasing the speed can improve the velocity distribution in the stirred tank very well.When the flow field completely enters the transitional flow state,if the speed is increased,the flow field velocity distribution will increase more.The structural analysis based on the bi-directional fluid-structure interaction method shows that the force coupling effect between the6 PBT impeller and the fluid is more obvious than that of the 6BT impeller.Besides,compared with 6BT impeller,6PBT impeller has stronger action force on fluid,better energy transfer and higher mixing efficiency.Due to the shear thinning property of the pseudoplastic fluid,as the rotational speed increases,the viscosity of the fluid gradually decreases,the force of the fluid on the blade also decreases accordingly,and the stress condition of the blade is improved.As the rheological index decreases,the viscosity of the pseudoplastic fluid increases,the viscous resistance and deformation of the blade are both increased.Modal analysis shows that the modal frequency of 6PBT impeller under prestressed mode is basically the same as that of natural mode.The rheological properties of pseudoplastic fluid have little effect on the natural frequency of 6PBT impeller,but have a certain influence on the vibration mode.