TU Dresden, Institute for Groundwater Management, D-01062 Dresden, Germany.
Ground Water. 2012 Jan-Feb;50(1):144-8. doi: 10.1111/j.1745-6584.2011.00805.x. Epub 2011 Mar 3.
As a result of rock dissolution processes, karst aquifers exhibit highly conductive features such as caves and conduits. Within these structures, groundwater flow can become turbulent and therefore be described by nonlinear gradient functions. Some numerical groundwater flow models explicitly account for pipe hydraulics by coupling the continuum model with a pipe network that represents the conduit system. In contrast, the Conduit Flow Process Mode 2 (CFPM2) for MODFLOW-2005 approximates turbulent flow by reducing the hydraulic conductivity within the existing linear head gradient of the MODFLOW continuum model. This approach reduces the practical as well as numerical efforts for simulating turbulence. The original formulation was for large pore aquifers where the onset of turbulence is at low Reynolds numbers (1 to 100) and not for conduits or pipes. In addition, the existing code requires multiple time steps for convergence due to iterative adjustment of the hydraulic conductivity. Modifications to the existing CFPM2 were made by implementing a generalized power function with a user-defined exponent. This allows for matching turbulence in porous media or pipes and eliminates the time steps required for iterative adjustment of hydraulic conductivity. The modified CFPM2 successfully replicated simple benchmark test problems.
由于岩石溶解过程，喀斯特含水层表现出高度传导的特征，如洞穴和管道。在这些结构中，地下水流动可能变得不稳定，因此可以用非线性梯度函数来描述。一些数值地下水流动模型通过将连续模型与代表管道系统的管网耦合，明确考虑到管道水力。相比之下，MODFLOW-2005 的管道流动过程模型 2（CFPM2）通过降低 MODFLOW 连续模型中现有线性水头梯度内的水力传导率来模拟不稳定流。这种方法减少了模拟不稳定流的实际和数值工作。原始公式适用于大孔隙含水层，其中不稳定流的起始雷诺数（1 到 100）较低，不适用于管道或管道。此外，由于水力传导率的迭代调整，现有代码需要多个时间步长才能收敛。通过实现具有用户定义指数的广义幂函数对现有 CFPM2 进行了修改。这允许在多孔介质或管道中匹配不稳定流，并消除了迭代调整水力传导率所需的时间步长。修改后的 CFPM2 成功复制了简单的基准测试问题。
