基于卸料流态模拟与观测的储粮仓壁动态压力增大机理研究

粮食筒仓在卸料过程中产生的动态侧压力是筒仓破坏的重要原因。该文基于室内粮食筒仓卸料模型试验,利用高速摄像仪拍摄筒仓中心卸料的全过程,运用图像处理技术分析贮料的流动形式,并测量卸料过程中产生的动态侧压力。在此试验的基础上,利用颗粒流程序PFC3D(particle flow code in 3 dimensions)进行数值模拟,追踪特定颗粒的运动情况。通过比较试验与数值模拟结果,从流态方面探索深仓中心卸料时超压现象产生的机理。研究表明:筒仓在卸料过程中动态侧压力在测点深度4 m的位置达到峰值15.92 kPa。卸料时存在着整体流动和管状流动2种流动形式,2种流动形式的混合区域主要分布在高径比约为1的高度位置,即中上部贮料进行整体流动,底部贮料进行管状流动,且底部贮料流动速度大于中上部贮料的流动速度。在2种流动形式混合区域容易产生承压拱,承压拱的存在阻碍了中上部贮料的正常流动,导致在该区域内产生明显的超压现象,最大超压系数达到2.5。通过研究筒仓在卸料过程中动态压力的增大机理,可为筒仓的安全设计提供参考。

Mechanism of dynamic pressure increase of grain silo wall based on simulation of discharge flow states

Abstract: Silo is widely used in grain, logistics, electric power, metallurgy and other industries. Therefore, the reasonable design of silo structure is the key. China is a large country of grain production, with application of the modern granary environmental protection, energy saving, green and other concepts, the cylinder wall is higher, and larger diameter, occupies less land, saves resources of the silo and is more and more in line with the future development trend of granary, and with the trend of rapid development around the world. With the increasing height and diameter of silo, the problem of failure in silo discharging is becoming more prominent. The dynamic lateral pressure of grain silo during discharging is the major cause of silo failure. In this paper, based on the indoor grain silo discharging model test, the whole process of the silo center emptying was recorded with high-speed camera, the flow pattern of grain was analyzed with image processing technology, and the dynamic pressure generated during the discharge process was measured. Based on this test, the particle flow code (PFC3D) was used to carry out numerical simulation to track the movement of specific particles in the test. By comparing the results of the experiment and the numerical simulation, the mechanism of overpressure in the discharge of the silo was explored. Through this study, in the process of discharging in the center, there were two kinds of flow states, the mass flow and the tubular flow. At the beginning of the discharge, the stored material flowed as mass flow. After a period of time, the upper part of the material flowed as mass flow, the bottom of the storage was a tubular flow, and the mass flow was in the high diameter ratio close to 1 of the height position to convert to tubular flow. When the discharging height reached 1.1m, the stored material flowed in tubular flow until the discharge was completed. Both the dynamic lateral pressure and the static lateral pressure increased with the depth of the measuring point, and the dynamic lateral pressure was greater than the static lateral pressure. At the beginning of the discharge, the dynamic lateral pressure measured by the silo suddenly increased, and then the dynamic lateral pressure value decreased with the continuous reduction of the storage height. The overpressure coefficient measured by the three groups of sensors was larger in the height range of the high diameter ratio close to 1, and the overpressure phenomenon was obvious. In the process of silo discharging, the speed of tubular flow of the bottom stored material was greater than the speed of the mass flow of the middle and upper stored material. There was a pressure arch at the junction of the two flow states, and the existence of the pressurized arch hindered the normal flow of the upper stored material, which led to the self-weight of the stored material and the additional force caused by the change of momentum was almost entirely by the arch, resulting in the increase of the dynamic lateral pressure and a significant overpressure phenomenon.