Experiment And Simulation Study On Granular Chute Flow With Turnings And Granular Merging Flow

Granular matter is the most common substance in nature. As a complex nonlinear dissipative system, its phase transition phenomenon is very complicated. The behavior of granular material is related to its packing history and packing order, so there is plenty of uncertainties which make some trouble in the studies. Till now, the physical essence of many granular phenomena is unclear, and the explanation remains in the qualitative level. The studies in granular material on the one hand can contribute to engineering problems, and on the other hand can promote the advance and interplay of statistical mechanics, nonlinear dynamics, traffic flow, applied mathematics and computer science.This paper is focused on granular chute flow, using experimental and simulation methods. Some new phenomena are presented in the paper, which will provide some bases for the understanding of the granular mechanisms. And the work also can provide some theoretical guidance to pipeline transport of particles, mixing of particles, and even traffic flow, etc.Usually the chute for the study of dilute to dense transition is vertical, while this paper changed the chute to inclined and with two turnings. The dilute to dense transition is observed by changing the width of the inclined chute. In the experiment, the transition is not abrupt, and there is a critical area, in which the final flow state can be either dilute state or dense state. So there is a bi-stable phenomenon for the same width of chute. The bi-stable region is determined in the experiment, and the discrete element method simulations show qualitatively agreement with experiment. Depending on the initial incoming flux, the upper one or the lower one of the two bottlenecks will become dense first. This determines the state of chute flow. In order to get more intuitive explain of the phenomenon, the two bottlenecks are simulated by DEM individually, and their dilute critical flow rate and dense flow rate are determined. In daily production and life, pipes with turnings are as common as vertical pipes. So the study of chutes with turnings gets some practical value.The merging flow of two channels is similar to the on-ramp system in traffic flow problem. The phase diagram of on-ramp system is usually studied in traffic flow aiming to optimize the traffic. Similarly, this paper studied the merging of two channels in order to solve the optimization problem of granular flow. In the experiment, by adjusting the opening width and thus the inflow of two channels, we observed nine flowing states for the system. The nine phases are presented in a phase diagram with coordinates of two channels’ incoming width. The resulting phase diagrams of granular merging flow are very similar to the on-ramp phase diagrams in traffic. And the simulation results are close to the results of experiment. Study of merging flow of two channels is valuable for the related engineering problem, debris flow, pedestrian flow and vehicular traffic flow.