Simulation Study On Dynamic Characteristics Of Agitator Shaft With Circular Stabilizer

Mixing equipment has been widely used in petroleum,chemical,pharmaceutical,food and other production areas,mixing plant including stirring shaft and the shaft rotational attachments,During the mixing process,The stirring shaft will vibrate axially,laterally and torsionally for the following reasons: the exciting force of the fluid,mixing the attachment installed eccentric,input speed fluctuations and other factors.The transverse bending vibration are the most common and most harmful,especially for thin stirring shaft,its natural frequency is low,and the axis of rotation speed and vibration frequency is close to easy to cause resonance,as a result,It is of great engineering significance to study the vibration characteristics of the mixing shaft,analyze the factors affecting the stability of the mixing shaft,predict the failure of the mixing shaft and find out the reasonable solutions.The literature shows that the stabilizer installed at the bottom of the stirring shaft can effectively resist the fluid exciting force in the stirring process,so as to reduce the deflection of the stirring shaft and reduce the transverse vibration.This paper is based on the fluid-solid coupling theory,CFD computational fluid mechanics method is used to simulate the fluid characteristics inside the stirring equipment,and the dynamic characteristics of the stirring shaft with stabilizer are analyzed.The experiment was carried out with a multi-functional experimental mixing device,and four stabilizers of different heights(30mm,40 mm,50mm,80mm)were installed for the six-blade open turbine agitator used in the experiment.In the finite element simulation analysis,this paper takes the existing experimental model(600mm long cantilever part and 300 mm distance between two supports)as an example to create a solid finite element model of agitator shaft-stabilizer,and analyzes the deflection and natural frequency of the agitator shaft under the agitator condition with the stabilizer of different heights and diameters.In the experimental study,an eddy current sensor was used to monitor the deflection of the agitator shaft with a circular stabilizer of different heights in real time.The results show that for the stirring shaft with circular stabilizers of different heights,the difference between the finite element calculation results of the axial end deflection and the experimental results is very small(less than 3 meters)when the rotational speed is lower than 100 rpm,with a difference of about 20%.With the increase of the rotational speed,the deflection value increases from 3 kept feet to 140 kept feet.The deflection difference calculated by the two methods increases from under 3 kept feet to 18 kept feet.The percentage of the deflection difference decreases.According to the calculation and analysis of the critical speed,the calculation result of the empirical formula is slightly less than that of the finite element simulation(less than 10%),so the calculation result of the finite element method is close to that of the experimental and empirical formula.Considering the errors of the existing equipment,the finite element model based on the fluid-solid coupling theory can be used to analyze the dynamic characteristics of the mixing shaft with stabilizer.Through finite element simulation calculation and analysis,it can be seen that: 1)for the mixing shaft with stabilizer,the fluctuation of flow field around the mixing blade becomes smaller.When the rotating speed is less than 200 rpm,compared with the mixing shaft without stabilizer,the pressure difference around the blades of the mixing shaft with four kinds of stabilizer heights(30mm,40 mm,50mm,80mm)fluctuates at25%.With the increase of rotating speed,the pressure difference near the blade increases.When the rotation speed is between 300 rpm and 380 rpm,among several stabilizers with the same diameter,the lower the height,the greater the pressure difference,and the overall pressure difference fluctuates around 35%.2)the size of the stabilizer has little influence on the first three natural frequencies of the mixing shaft(the increase in height by 10 mm or in diameter by 50 mm will cause a 1Hz change).The natural frequencies of the fourth to sixth order will decrease significantly with the increase in the size of the stabilizer(the increase in height by 10 mm or in diameter by50 mm will cause at least a 30 Hz change).3)when the rotating speed of the stirring shaft is less than 200 rpm,the deflection of the stabilizers of all sizes decreases slightly,and all of them can reduce the deflection by about 50%.When the rotating speed is between220 rpm and 380 rpm,the percentage of deflection reduction is related to the stabilizer size: the deflection reduction of the stabilizer with a radius of 200 mm and a height of80 mm is about 5% more than that of the stabilizer with a radius of 200 mm and a height of 30 mm.The deflection of the stabilizer with a height of 50 mm and a radius of 250 mm is reduced by about 10% more than that with a height of 100 mm.