共查询到15条相似文献,搜索用时 125 毫秒
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在此之前已经报道了二维斜面颗粒流在通道中的分布规律以及二维斜面粗糙边界附近的颗粒 流量密度(ξ=ρ·ν)分布.本文则主要研究通道宽度W对边界附近颗粒流量密度(ξ=ρ· ν)分布的影响.结果表明,颗粒流量密度随通道宽度的变化(ξ W)存在一临界通道宽度W c.在本实验条件下临界通道宽度Wc=70d.当通道宽度小于临界宽度Wc时 ,通道中距边界20d—30d区间内的相对颗粒流量密度随斜面倾斜角的变化可描述为ξ∝( sinθ)α,α是与通道宽度W有关的参数,其数值在032至085之间.
关键词:
二维颗粒流
颗粒物质
颗粒流量密度 相似文献
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以往的实验研究中,已经知道粗糙边界条件下,二维颗粒流的颗粒流量是以通道中心横向对称分布的,颗粒流横向分布既受通道宽度的影响,同时也受通道斜面倾斜角的影响,而且颗粒在通道两侧的分布明显少于通道中间. 主要研究粗糙边界附近颗粒分布随通道宽度以及通道斜面倾斜角的变化规律. 在稀疏流状态以及保持边界墙体的粗糙度不变的条件下,对应不同通道宽度,粗糙边界附近10d范围内的颗粒流量密度(ξ=ρv)随斜面倾斜角的增大而减小,颗粒流量密度随通道宽度的变化存在一临界宽度Wc;在通道宽度小于Wc时,粗糙墙体附近10d范围内颗粒流量密度ξ随sinθ呈指数衰减,通道宽度大于Wc时,颗粒流量密度ξ_sinθ曲线随θ增大几乎呈线性减小.
关键词:
二维颗粒流
颗粒物质
颗粒流量密度 相似文献
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通过用分子动力学方法对颗粒物质流的计算机模拟,研究发现增大通道宽度可以使二维颗粒流从稀疏流转变为密集流状态.通过对不同通道宽度下,固定开口为9.5d的颗粒流和 漏斗口以上9.5d×8d区域记录的模拟结果分析,发现随通道宽度增大,密度变大、温 度降低.当“颗粒温度”T较低时(T/m<0.05 J/kg),颗粒流内部接触数开始超过1.2 ,同时出现较为牢固的横向链状颗粒团簇,是造成流量突变以及密集流的原因.
关键词:
颗粒物质
颗粒流
计算机模拟 相似文献
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用计算机模拟的方法研究了开口角度对二维颗粒流稀疏流—密集流转变的影响.在固定入口流量和固定颗粒数两种条件下,均发现当开口角度大于零时,开口角度的增大可以提高颗粒流由稀疏流向密集流转变的最大出口流量.在稀疏流状态下,出口流量与开口角度无关;而在密集流状态下,出口流量随开口角度的增大而增大.进一步的计算还发现增加开口角度可以提高颗粒流出开口的流动速度,且最大出口流量与颗粒的流动速度呈线性关系.
关键词:
颗粒物质
颗粒流
分子动力学模拟 相似文献
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用实验和计算模拟的方法研究了颗粒流中的颗粒速度与颗粒流特性的关系.实验研究发现当入口流量固定时,在出口上方高速运动的颗粒会使颗粒流由稀疏流向密集流转变的临界出口尺寸变小.当颗粒流转变为密集流后,颗粒速度的作用被出口上方的颗粒堆积区所消耗,最终变得与颗粒速度无关.二维分子动力学模拟计算得到了与实验相同的结论.通过二维分子动力学模拟计算,还给出了不同颗粒速度下体系的密度和速率在空间的分布图.这些分布图显示随着颗粒到达出口上方的瞬间速度的不同,颗粒堆积区的密度和高度均会改变,并最终导致颗粒流流动状态的改变.
关键词:
颗粒流
颗粒气体
分子动力学模拟 相似文献
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实验研究了粗糙边界条件、不同通道宽度以及不同斜面倾斜角下二维颗粒流的颗粒分布 ,发现颗粒流在稀疏流状态下尽管在现象上表现出类似流体的性质,但由于颗粒流系统的能 量耗散,所以颗粒流的速度和密度分布和牛顿流体完全不同,颗粒流在通道中的分布既受通 道宽度的影响同时也受重力场的影响,颗粒在通道中以通道中轴线呈对称分布,通道两侧的 颗粒密度明显高于通道中间,由于通道中颗粒受剪切力的作用,导致颗粒在通道中的密度分 布的变化,通道边界粗糙度明显影响着颗粒流横向分布.
关键词:
二维颗粒流
颗粒物质
稀疏流 相似文献
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The dilute-to-dense transition of granular flow of particle size d(0) is studied experimentally in a two-dimensional channel (width D) with confined exit (width d). Our results show that with fixed d and D there is a maximum inflow rate Q(c) above which the flow changes from dilute to dense and the outflow rate
drops abruptly from Q(c) to a dense rate Q(d). A rescaled critical rate q(c) is found to be a function of a scaling variable lambda only: q(c) approximately F(lambda), where lambda identical with d/d(0) d/D-d. This form of lambda suggests that the dilute-to-dense transition is a global property of the flow, unlike the jamming transition which depends only on d/d(0). Furthermore, the transition is found to occur when the area fraction of particles near the exit exceeds a critical value which is close to 0.65+/-0.03. 相似文献
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HUANG De-Cai SUN Gang LU Kun-Quan 《理论物理通讯》2007,48(4):729-733
Two-dimensional granular flow in a channel with small exit is studied by molecular dyhamics simulations. We firstly define a key area near the exit, which is considered to be the choke area of the system. Then we observe the time variation of the local packing fraction and flow rate in this area for several fixed inflow rate, and find that these quantities change abruptly when the transition from dilute flow state to dense flow state happens. A relationship between the local flow rate and the local packing fraction in the key area is also given. The relationship is a continuous function under the fixed particle number condition, and has the characteristic that the flow rate has a maximum at a moderate packing fraction and the packing fraction is terminated at a high value with negative slope. By use of the relationship, the properties of the flow states under the fixed inflow rate condition are discussed in detail, and the discontinuities and the complex time variation behavior observed'in the preexisting works are naturally explained by a stochastic process. 相似文献
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《Physics letters. A》2014,378(18-19):1281-1285
This paper studies the granular flow down a chute with two successive turnings, which play the role of bottlenecks for the granular flow system and determine the granular flow state in main section between them. With the increase of main section width D, phase transition from dilute to dense granular flow is observed: When the main section width D is small (large), the granular flow at upper (lower) bottleneck is dense and the granular flow is dilute (dense) in the main section. More interestingly, a bistable region is exhibited, in which either dilute flow or dense flow may occur and continue for the entire run. In this region, the packing in the reservoir will affect initial flow rate and then affect the flow pattern. This study can be viewed as a paradigm for the jamming and unjamming transitions under shear due to gravity. 相似文献
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In this Letter, we present the results of our study on the influence of granule velocity on the granular flow state. The maximum outflow rate of the dilute flow state increases with an increase in granule velocity, whereas the outflow rate of the dense flow state remains unchanged. In addition, increasing granule velocity can extend the region of the dilute flow state and shrink that of the dense flow state. These observations can be explained by the relationship between the flow rate and the packing fraction at the bottleneck under a fixed particle number condition. 相似文献