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等效水力隙宽和水力梯度是影响岩体裂隙网络渗流特性的重要因素。制作裂隙网络试验模型,建立高精度渗流试验系统;求解纳维-斯托克斯方程,模拟流体在裂隙网络内的流动状态,研究等效水力隙宽和水力梯度对非线性渗流特性的影响。结果表明,当水力梯度较小时,等效渗透系数保持恒定的常数,流体流动属于达西流动区域,流量与压力具有线性关系,可采用立方定律计算流体流动;当水力梯度较大时,等效渗透系数随着水力梯度的增加而急剧减少,流体流动进入强惯性效应流动区域,流量与压力具有强烈的非线性关系,可采用Forchheimer方程计算流体流动。随着等效水力隙宽的增加,区别线性和非线性流动区域的临界水力梯度呈幂函数关系递减。当水力梯度小于临界水力梯度时,控制方程可选立方定律;当水力梯度大于临界水力梯度时,控制方程可选Forchheimer方程,其参数A和B可根据经验公式计算得到。其研究结果可为临界水力梯度的确定及流体流动控制方程的选取提供借鉴意义。
Equivalent hydraulic gap width and hydraulic gradient are important factors affecting the seepage characteristics of rock fracture network. The fracture network test model was established to establish a high-precision seepage test system. The Navier-Stokes equations were solved to simulate the fluid flow in the fracture network. The effects of equivalent hydraulic gap width and hydraulic gradient on the nonlinear seepage characteristics were studied. The results show that when the hydraulic gradient is small, the equivalent permeability coefficient remains a constant, the fluid flow belongs to the Darcy flow region, and the flow and pressure have a linear relationship. The cubic law can be used to calculate the fluid flow. When the hydraulic gradient is large, the equivalence The permeability coefficient drastically decreases with the increase of hydraulic gradient, and the fluid flow enters the strong inertia effect flow area. The flow and pressure have a strong non-linear relationship. Forchheimer equation can be used to calculate the fluid flow. With the increase of equivalent hydraulic gap width, the critical hydraulic gradient that differentiates between linear and non-linear flow areas decreases exponentially. When the hydraulic gradient is less than the critical hydraulic gradient, the governing equation can be selected as the cubic law. When the hydraulic gradient is greater than the critical hydraulic gradient, the governing equation can be selected as the Forchheimer equation. The parameters A and B can be calculated according to the empirical formula. The results of this study can provide reference for the determination of critical hydraulic gradient and the selection of fluid flow control equations.