Study Of Fluid-structure Interaction Characteristics Of Flexible Blade In A Stirred Tank

Stirring is a common operation unit in the chemical industry,the structural stress and fluid flow in the stirred tank have important impact on the safety and efficiency of chemical process.Baffles,propeller,shaft and other components get structural deformation when they subjected to fluid forces.This deformation affects the fluid movement around the structure and intensifies the instability of flow,which causes the stirring structure get another deformation.The interaction of fluid and structure in stirred reactor is called fluid-solid interaction phenomenon.In this paper,the experiment is carried out in a circular stirred tank with a diameter of 480 mm and full baffle.Flexible blades are made of super elastic NiTi alloy.The deformation of flexible blade at different speeds is captured using high speed camera during high frequency shooting.The average deformation at each rotating speed is obtained and the vibration characteristics are investigated.It is found that the balance position,displacement amplitude and amplitude fluctuation increase with the increasing rotational speed.Baffle has a certain effect on the deformation of the blade.The blade deformation is small when pass by the baffle and is large between the baffle.According to the average deformation of flexible blade,rigid curved blade is made of high carbon steel.The stirring shaft moment(including bending moment and torque)is obtained by a high-precision sensor.We can learn that under the same speed,the bending moment of flexible blade is slightly higher than that of rigid blade;the difference of moment amplitude of two kinds of impellers is very small;the torque of flexible blade is greater than the rigid obviously.Using the PIV technique,the phase resolution fluid field and the phase averaging data of the two impellers are obtained at the same speed or power.We can find that under same speed or power,trailing vortex movement of two impellers is similar,the position of flexible one is closer to the tank wall in the radial direction,the velocity field is basically alike.The high turbulence kinetic energy area and the high turbulence kinetic energy dispersion area of the flexible impeller are larger and more far away from the blade than those of the rigid curved blade at each phase.The swing of flexible blade has great effect on the fluid motion in the impeller region,and it can transfer more energy of fluid in radial direction.