射流伺服阀前置级颗粒物空间分布数值研究

为了研究油液中所携带的颗粒物在伺服阀前置级中的停留率和停留位置,本研究通过数值模拟研究了在不同工作状态下,不同尺寸的固体颗粒在射流伺服阀前置级流场中的速度空间分布。结果表明:(1)颗粒会在伺服阀前置级中展现出倾向性的聚集行为,且长时间驻留在伺服阀内,特别是接收口及以下区域;(2)控制腔C1、C2端面边界条件为正弦流率相比其为固定壁面时,颗粒相的停留率更低;(3)控制腔端面C1、C2边界条件为正弦流率时,伺服阀前置级内颗粒停留率展现出随时间延长而降低的趋势。

Size dependent flow behaviors of particles in hydrocyclone based on multiphase simulation

To investigate the flow behaviors of different size particles in hydrocyclone,a designed process was numerically simulated by the transient solver,where the quartz particles possessing a size distribution were injected into a 100 mm diameter hydrocyclone with the steady water field and air core inside.A lab experimental work has validated the chosen models in simulation by comparing the classification efficiency results.The simulated process shows that the 25 μm quartz particles,close to the cut size,need much more time than the finer and coarser particles to reach the steady flow rate on the outlets of hydrocyclone.For the particles in the inner swirl,with the quartz size increasing from 5 to 25 μm,the particles take more time to enter the vortex finder.The 25 μm quartz particles move outward in the radial direction when they go up to the vortex finder,which is contrary to the quartz particles of 5 μm and 15 μm as they are closely surrounding the air core.The studies reveal that the flow behaviors of particles inside the hydrocyclone depend on the particle size.

Hydrodynamics and Solids Mixing Behavior in a Riser with Blunt Internals

The hydrodynamics and solids mixing behavior in a riser with blunt internals are studied. A uniform radial distribution for solids fraction and particle velocity achieves near the internals. The turbulent velocity of particles near the wall increases with the addition of the internals, with the lateral solids mixing enhanced significantly. Probability density distribution of particle velocity is bimodal in the riser with internals, which is similar to that in the conventional riser, indicating that no significant difference in the micro flow structure exists between the riser with internals and the conventional riser. At the same time, the axial solids mixing behavior changes insignificantly with the addition of internals. These results indicate that the micro flow structure in the riser is very stable, which changes insignificantly with the change of the bed structure.

A novel non-overlapping approach to accurately represent 2D arbitrary particles for DEM modelling

Mechanical behaviors of granular materials are complicated and greatly influenced by the particle shape.Current,some composite approaches have been proposed for realistic particle shape modelling within discrete element method(DEM),while they cannot give a good representation to the shape and mass properties of a real particle.In this work,a novel algorithm is developed to model an arbitrary particle using a cluster of non-overlapping disks.The algorithm mainly consists of two components:boundary filling and domain filling.In the boundary filling,some disks are placed along the boundary for a precise representation of the particle shape,and some more disks are placed in the domain to give an approximation to the mass properties of the particle in the domain filling.Besides,a simple method is proposed to correct the mass properties of a cluster after domain filling and reduce the number of the disks in a cluster for lower computational load.Moreover,it is another great merit of the algorithm that a cluster generated by the algorithm can be used to simulate the particle breakage because of no overlaps between the disks in a cluster.Finally,several examples are used to show the robust performance of the algorithm.A current FORTRAN version of the algorithm is available by contacting the author.

Discrete numerical modeling of granular materials considering crushability

The aim of this study is to numerically investigate the influence of particle breakage on the mechanical behavior of granular materials using a discrete element method(DEM). To enable particle crushing, non-crushable elementary particles are boned together to represents the granular aggregates which can be crushed when the external force exceeds its strength. The flaw of the aggregate was also modeled by randomly distributed void. Single particle crushing tests were carried out to determine the distribution of particle strength. The results of single particle crushing tests illustrate that the simulated single particle fracture strength and pattern agree well with the Weibull's distribution equation.Conventional oedometer tests, drained monotonic and cyclic triaxial tests were also carried out to investigate the crushing of the aggregates and the associated mechanical behaviors. The effect of confining pressure on the crushing of aggregates and the mechanical behavior was also analyzed. It was found that the peak stress and dilation decrease significantly when particle crushing was considered.The deformation behavior of the specimen is essentially controlled by two factors: particle rearrangement-induced dilation and particle crushing-induced contraction. The increase of permanent strain and the reduction of dilation were observed during cyclic loading and they tend to reach a stable state after a certain number of cycles. The crushing of aggregate is most significant in the first two cycles. The results also indicated that for the same axial strain the volumetric strain and the bound breakage in the cyclic loading tests are significantly larger than that in the monotonic loading tests,especially at high cyclic stress ratio.