| Summary: | 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.
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