两种不同粒径石英砂中非达西流动的实验研究

Experimental study on non-Darcian flow in two kinds of media with different diameters

在水力梯度较大的多孔介质中，水流往往呈现非达西现象。为分析不同粒径介质中非达西流发生的条件，本文对粒径为0．5～0．63mm和0．63～1．25mm两种石英砂，分别开展了一维均质土柱渗流实验，并应用水力阻抗和临界雷诺数判别渗流过程的非达西现象。研究结果表明，随着渗透流速增大，水力梯度和渗透流速之间的线性关系将发生偏移，且Forehheimer方程和Izbash方程均能够很好地描述非达西渗流阶段的水流运动过程。此时，水力梯度中以黏性力和惯性力消耗能量为主导的渗透流速线性项和非线性项均逐渐增大，同时非线性项占水力梯度的相对比重随流速的增大而不断增大。两种石英砂出现非达西流时，其非线性项占水力梯度的40％～50％，相应的临界雷诺数分别为22～27和52～104。非达西流出现的临界雷诺数随介质粒径的增大而增大。

The linear relationship between the hydraulic gradient and specific discharge for Darcy＇s law is no longer valid when the specific discharge is large enough. This means that non-Darcian flow occurs. An experiment was conducted by using 1-D sand columns with various hydraulic gradients to establish the relationship between the hydraulic gradient and specific discharge passing through two kinds of porous media with diameters of 0.5mm - 0.63mm and 0.63mm - 1.25mm respectively. The hydraulic resistivity and Reynolds number were used to identify the occurrence of non-Darcian flow. The results indicate that both the Forcheimer and lzbash equations can well describe the flow. Both the linear term and nonlinear term of hydraulic gradient representing the energy dissipation due to inertia force and viscous force respectively are increasing with the increase of specific discharge. At the same time, the portion of nonlinear term in hydraulic gradient increases continuously. The nonlinear term of hydraulic gradient is 40% and 50%, and the critical Reynolds number is 22 - 27 and 52 - 104 for two kinds of media respectively. The critical Reynolds number for occurring of non-Darcian flow increases with grain diameter.