Interaction Mechanism Of Flow Around Porous Particles Based On Lattice Boltzmann Method

Flow around porous bluff bodies widely exists in nature and various engineering fields,such as life sciences,energy and chemical engineering,aerospace,nuclear and ocean engineering.The fluid-solid system of such porous particles involves the interaction between internal and external solid skeletons and fluids.It has important academic and application value to deeply study and reveal its internal mechanism and flow law.At present,considerable work has been done on numerical studies of the flow around porous bluff bodys,but there are few reports on the effects of multiple bluff body arrangements on vortex shedding patterns and forces acting on bluff bodies.Based on this,this paper adopts the mesoscopic lattice Boltzmann method(lattice Boltzmann method)to conduct numerical simulation and mechanism analysis of the flow around porous particles with a Reynolds number(Re)of 100 and a Darcy number(Da)within the typical flow characteristics range of 10-6≤Da≤10-2.By examining the side by side and tandem arrangement of double porous particles,as well as the structural arrangement of three particles in an equilateral triangle,to explore the mechanism of the influence of different spacing ratios(T/D for side by side,L/D for tandem,and three particles)and Da on the vortex shedding and its frequency and force coefficient.The main research results are as follows:When the porous particles are arranged side by side,seven flow pattern are observed in this paper,with five in the range of 10-6≤Da≤10-3,and one in the small Da range(10-6≤Da≤10-4)another in the range of Da=10-2.When Da=10-2,vortex shedding never forms,the flow pattern hardly changes with the spacing ratio,and the force coefficient almost assumes a straight line shape without fluctuations.When 1.1≤T/D≤1.3,reducing Da will delay the development of the flow pattern to the next stage by weakening the effect of interstitial flow;When 1.4≤T/D≤1.5,reducing Da will promote the transition of flow pattern.In addition,it is also found that the drag coefficients of both particles have a step phenomenon,and the average lift coefficient is negatively correlated with Da.The vortex shedding frequency increases with the increase of the spacing ratio,but is less affected by Da.For the arrangement of porous particles in tandem,it is found that there are three flow patterns,namely,the flow mode 1 in which only downstream vortex shedding occurs,the flow mode 2 in which both particles have vortex shedding,and the flow mode 3 in which no vortex shedding occurs.When Da=10-2,downstream particles will form vortex shedding,but the vortex shedding phenomenon quickly disappears as the spacing ratio increases.When Da is within the range of 10-6≤Da≤10-3,reducing Da will promote the flow pattern to enter mode 2 faster.In particular,in mode 1,the vortex shedding frequency decreases as the spacing ratio increases,while in mode 2,the vortex shedding frequency hardly changes with the spacing ratio.For the lift coefficient,the smaller the Da,the stronger the fluctuation.However,the step phenomenon of the drag coefficient only occurs at the upstream particles,while the downstream particles have a negative correlation with Da.When three porous particles are arranged in an equilateral triangle,ten flow patterns are found in this paper.When Da=10-2,there are four flow patterns.The shear layer strength of upstream particles increases with the increase of spacing ratio in the range of 1.6≤L/D≤3.2 and decreases with the increase of spacing ratio in the range of 3.4≤L/D≤6.0.When 10-6≤Da≤10-3,there are three flow patterns within the range of 1.2≤L/D≤2.6 that correspond to the side by side arrangement of two particles and have similar vortex shedding patterns.When 1.2≤L/D≤1.8,reducing Da will delay the transition of the flow pattern;When 2.0≤L/D≤2.6,only when Da=10-6 flow pattern transition can be promoted.When 2.8≤L/D≤6.0,there are three flow patterns,and there is only one flow pattern within the small Da range.In addition,this paper also found that the vortex shedding frequencies of the three particles are not equal at 1.4≤L/D≤2.6,while the vortex shedding frequencies of the upstream particles are slower,and the vortex shedding frequencies of the three particles are consistent for other spacing ratios.The drag coefficients at the three particles all have a step phenomenon,and their average lift coefficients change with the increase of the spacing ratio.The fluctuation of the two force coefficients is still inversely proportional to Da.