基于表面反应和扩散迁移控制的灰岩单裂隙渗流—溶解模型及其数值模拟

Model of Coupled Fluid Flow and Chemical Dissolution Controlled by Surface Reaction and Mass Transfer in a Single Limestone Fracture and Its Numerical Simulation

针对碳酸盐类可溶岩地区水电站坝址流场、化学场及固相介质属性等随时间发生改变对工程安全运行造成不利影响等问题,研究了灰岩地区地下水运移过程中各物理场间的相互作用,分析了影响灰岩溶解速率的2个因素,即表面反应控制和扩散迁移控制。在此基础上,建立了单裂隙中的渗流—溶解耦合模型,并进行数值求解。模拟结果表明:在垂直裂隙延伸方向,其溶蚀锋面不为齐整平面,而是呈似"虫洞"状非均一变化,而沿裂隙延伸方向即自上游侧向下游方向溶蚀程度逐渐减轻;通过裂隙的流量呈现随时间逐渐增大的趋势,但变幅不大;根据流量求得的等效水力隙宽,其增幅和增长速率均小于实际平均隙宽;同时,化学场中Ca2+浓度的分布与裂隙开度变化具有相似性,不同时刻上游侧反应速率R均大于下游侧;就反应机制而言,初期均受表面反应控制,随反应进行,位于上游的补给区部位转为受扩散迁移控制,但在下游位置仍受表面反应控制。

Some hydropower stations were built on soluble rocks such as carbonate and the flow field,chemical field and solid properties around a dam site were changed,which may have adverse effect on the operation. Two factors,surface reaction and mass transfer,were thought to control the dissolution process. Based on this,a model of coupled fluid flow and chemical dissolution in a single fracture was built up and solved. And the results showed that the dissolution front is not a plane,but somehow like wormholes. And the aperture along the fracture becomes narrower. Although the flow through the fracture becomes larger,the amplitude was small. And the range and growth rate of equivalent hydraulic aperture are much smaller than actual average aperture. The distribution of Ca2 +concentration is similar to the aperture,while the reaction rate at upstream is much faster than the one at downstream. And along the whole fracture it is controlled by surface reaction initially. As the dissolution processing,it turns to mass transfer control near the inlet,while it remains surface reaction controlled near the downstream.