A new method for selecting dimensionless relaxation time in the lattice Boltzmann model was proposed based on similarity criterion and gas true physical parameters.At the same time,the dimensionless relaxation time wa...A new method for selecting dimensionless relaxation time in the lattice Boltzmann model was proposed based on similarity criterion and gas true physical parameters.At the same time,the dimensionless relaxation time was modified by considering the influence of the boundary Knudsen layer.On this basis,the second-order slip boundary condition of the wall was considered,and the key parameters in the corresponding combined bounce-back/specular-reflection boundary condition were deduced to build a new model of unconventional gas microscale flow simulation based on the lattice Boltzmann method suitable for high temperatures and high pressures.The simulation results of methane gas flow driven by body force in infinite micro-channels and flow driven by inlet-outlet pressure differential in long straight channels were compared with the numerical and analytical solutions in the literature to verify the accuracy of the model,and the dimensionless relaxation time modification was formally optimized.The results show that the new model can effectively characterize the slippage effect,compression effect,gas density and the effect of boundary Knudsen layer in the micro-scale flow of unconventional natural gas.The new model can achieve a more comprehensive characterization of the real gas flow conditions and can be used as a basic model for the simulation of unconventional gas flow on the micro-nano scale.展开更多
The flow performances of water, white oil and Hydrolyzing Polyacrylamide (HPAM) solution in fused quartz channels and the effect of wettability on the microscale flows have been studied respectively in this paper. The...The flow performances of water, white oil and Hydrolyzing Polyacrylamide (HPAM) solution in fused quartz channels and the effect of wettability on the microscale flows have been studied respectively in this paper. The adaptability of classical fluid mechanics in channels with different sizes has been discussed. The results show that water flows in channels of 2μm diameter also have few size effects and white oil flow accord with classical fluid mechanics theory in channels of 25μm diameter too, but polymer solution appears an obvious size effect as diameters of channels decrease to 16μm. The wettability does not produce any influences on the water or white oil flows in channels of 25μm or 50μm diameter. The experimental technology of microscale flows has been first applied for studying the flow performances of pores in low permeability reservoir. This study found a base for deep investigating the percolation mechanism in low permeability reservoirs.展开更多
It is well known that Navier-Stokes equations are not valid for those high-Knudsen and high-Mach flows, in which the local thermodynamically non-equilibrium effects are dominant. To extend the non-equilibrium describi...It is well known that Navier-Stokes equations are not valid for those high-Knudsen and high-Mach flows, in which the local thermodynamically non-equilibrium effects are dominant. To extend the non-equilibrium describing the ability of macroscopic equations, Nonlinear Coupled Constitutive Relation(NCCR) model was developed from Eu’s generalized hydrodynamic equations to substitute linear Newton’s law of viscosity and Fourier’s law of heat conduction in conservation laws. In the NCCR model, how to solve the decomposed constitutive equations with reasonable computational cost is a key ingredient of this scheme. In this paper, an analytic method is proposed firstly. Compared to the iterative procedure in the conventional NCCR model, the analytic method not only obtains exact roots of the decomposed constitutive polynomials, but also preserves the nonlinear constitutive relations in the original framework of NCCR methods. Numerical tests to assess the efficiency and accuracy of the proposed method are conducted for argon shock structures, Couette flows, two-dimensional hypersonic flows over a cylinder and threedimensional supersonic flows over a three-dimensional sphere. These superior advantages of the current method are expected to render itself a powerful tool for simulating the hypersonic rarefied flows and microscale flows of high Knudsen number for engineering applications.展开更多
基金Supported by National Natural Science Foundation of China(Key Program)(51534006)National Natural Science Foundation of China(51874251)。
文摘A new method for selecting dimensionless relaxation time in the lattice Boltzmann model was proposed based on similarity criterion and gas true physical parameters.At the same time,the dimensionless relaxation time was modified by considering the influence of the boundary Knudsen layer.On this basis,the second-order slip boundary condition of the wall was considered,and the key parameters in the corresponding combined bounce-back/specular-reflection boundary condition were deduced to build a new model of unconventional gas microscale flow simulation based on the lattice Boltzmann method suitable for high temperatures and high pressures.The simulation results of methane gas flow driven by body force in infinite micro-channels and flow driven by inlet-outlet pressure differential in long straight channels were compared with the numerical and analytical solutions in the literature to verify the accuracy of the model,and the dimensionless relaxation time modification was formally optimized.The results show that the new model can effectively characterize the slippage effect,compression effect,gas density and the effect of boundary Knudsen layer in the micro-scale flow of unconventional natural gas.The new model can achieve a more comprehensive characterization of the real gas flow conditions and can be used as a basic model for the simulation of unconventional gas flow on the micro-nano scale.
文摘The flow performances of water, white oil and Hydrolyzing Polyacrylamide (HPAM) solution in fused quartz channels and the effect of wettability on the microscale flows have been studied respectively in this paper. The adaptability of classical fluid mechanics in channels with different sizes has been discussed. The results show that water flows in channels of 2μm diameter also have few size effects and white oil flow accord with classical fluid mechanics theory in channels of 25μm diameter too, but polymer solution appears an obvious size effect as diameters of channels decrease to 16μm. The wettability does not produce any influences on the water or white oil flows in channels of 25μm or 50μm diameter. The experimental technology of microscale flows has been first applied for studying the flow performances of pores in low permeability reservoir. This study found a base for deep investigating the percolation mechanism in low permeability reservoirs.
基金financially supported by the National Natural Science Foundation of China (Nos.:11502232, 51575487,11572284, and 6162790014)support by the China Scholarship Council (No.201906320279)partially performed on resources of the National Supercomputing Centre,Singapore (https://www.nscc.sg)。
文摘It is well known that Navier-Stokes equations are not valid for those high-Knudsen and high-Mach flows, in which the local thermodynamically non-equilibrium effects are dominant. To extend the non-equilibrium describing the ability of macroscopic equations, Nonlinear Coupled Constitutive Relation(NCCR) model was developed from Eu’s generalized hydrodynamic equations to substitute linear Newton’s law of viscosity and Fourier’s law of heat conduction in conservation laws. In the NCCR model, how to solve the decomposed constitutive equations with reasonable computational cost is a key ingredient of this scheme. In this paper, an analytic method is proposed firstly. Compared to the iterative procedure in the conventional NCCR model, the analytic method not only obtains exact roots of the decomposed constitutive polynomials, but also preserves the nonlinear constitutive relations in the original framework of NCCR methods. Numerical tests to assess the efficiency and accuracy of the proposed method are conducted for argon shock structures, Couette flows, two-dimensional hypersonic flows over a cylinder and threedimensional supersonic flows over a three-dimensional sphere. These superior advantages of the current method are expected to render itself a powerful tool for simulating the hypersonic rarefied flows and microscale flows of high Knudsen number for engineering applications.
