Study On Discharge Flow Pattern And Dynamic Lateral Pressure Of Silo Considering The Influence Of Hopper Inclination

As an important tubular structure,silos are widely used in grain storage industry.With the increasing number of silos,the safety design of silos structure becomes more and more important.In silo structure design,selecting more reasonable storage pressure value is an important premise to ensure silo safety and reliability.The dynamic side pressure of silos is much higher than the static side pressure in the unloading process,which has been widely accepted by the academia.However,no consensus has been reached on the increasing mechanism of dynamic lateral pressure and the distribution of overpressure phenomenon.When central unloading is carried out in the silo,the difference of funnel inclination will affect the discharging flow patterns and lead to the change of dynamic side pressure.In this paper,based on the national natural fund project:"based on the loading process of energy conversion silo dynamic overpressure mechanism"（51578216）,through the laboratory model test,numerical simulation and theoretical derivation method,from the silo discharging flow patterns and the principle of arch’s perspective,to explore the silo dynamic mechanism of the increase of confining pressure unloading process,provide a reference for the safety of the silo design,the main contents are as follows:（1）In the laboratory model test,plexiglass silos with inclination angles of 30 degrees,45degrees and 60 degrees funnel were selected,and the storage materials were layered with soybeans and black beans with the same grain size.The earth pressure sensors installed in the inner wall of the silo are used to measure the lateral pressure of the storage material and record the flow of the storage material during unloading.The static side pressure value,the standard value and the dynamic side pressure value were compared and analyzed respectively,and the overpressure coefficient of each measuring point was calculated to get the maximum overpressure coefficient and the distribution range of overpressure phenomenon.The relationship between flow state and dynamic overpressure is analyzed by observing the flow of layered storage during unloading.（2）Use particle flow code PFC^2D to establish the same model silo as the test,and generate storage particles in layers.The static side pressure obtained by the simulation is not far from the standard value.On this basis,dynamic side pressure measurement and flow record during discharging are carried out.According to the difference of flow pattern,the comparison of velocity field and force chain diagram,and the comparison of experimental results,the mechanism of increasing dynamic lateral pressure was further studied.（3）Based on the results of indoor model test and numerical simulation,the following conclusions can be drawn:the difference in funnel Angle does not affect the static lateral pressure of the silo side wall,and the dynamic lateral pressure decreases with the increase of the height of the measuring point;For the same height of measurement point,the smaller the funnel Angle is,the larger the dynamic lateral pressure value is and the larger the overpressure coefficient is.Different funnel inclinations result in different junction positions of the two flow forms.The junction position of flow pattern almost coincides with the significant overpressure area.The difference of flow pattern changes leads to different velocity at the junction,which leads to the increase of dynamic lateral pressure.（4）According to the principle of flow and camber formation of the storage material,the principle of increasing the dynamic lateral pressure in the unloading process of the silo is analyzed from the perspective of the flow pattern of the storage material.According to the experimental and numerical simulation results,the silo has bothmass flow and tubular flow in the unloading process,and it is easy to produce pressure arch at the junction of the two flow forms.The existence of pressure arch will hinder the normal flow of storage material,resulting in the inertia force completely acting on the arch body,and then leading to the increase of dynamic lateral pressure.The difference of funnel inclination Angle mainly affects the position of pressure-bearing arch.The larger the funnel inclination Angle is,the closer the position of pressure-bearing arch is to the bottom of the silo wall.On this basis,the equation is established for theoretical analysis,and the calculation formula of dynamic lateral pressure is obtained.The calculated value is compared with the experimental value and the simulated value,and the results of the three are relatively close.