岩溶洞穴的强迫流示踪实验模型与数值模拟

Forced Convection Tracer Experimental Model and Numerical Simulation of Karst Cave

提出了一种用于计算钻孔揭露的岩溶洞穴体积的新方法—强迫流示踪法,即在钻孔揭露的岩溶洞穴中定量投放示踪剂后,将小型搅拌设备放入洞穴中,强力搅拌洞穴中水体,使示踪剂迅速扩散至整个洞穴空间,同时观测搅拌中心的示踪剂浓度变化,得到示踪剂浓度历时曲线,依据不同的示踪剂浓度历时曲线计算不同类型洞穴的体积.本文还同时提出了一维、二维和三维封闭岩溶洞穴在强迫流条件下的示踪曲线概化模型,并通过数值模拟验证了这些模型.封闭岩溶洞穴的强迫流示踪模型表明,每个(或与搅拌中心等距的每组)洞穴的开阔壁面均有可能使搅拌中心的示踪剂浓度历时曲线产生一个拐弯点,壁面离搅拌中心越近,拐弯点越明显,随着距离的增大,拐弯点不明显;拐弯点出现的时间与示踪剂在强迫流条件下到达洞穴壁面的时间有关,壁面距搅拌中心越近,两者的一致性越好,距离越远,拐弯点出现时间越滞后于示踪剂到达洞穴壁面的时间.

A new method, namely Forced Convection Tracer Method （FCTM）for calculating the volume of drilling-revealed subsurface karst cave, was presented in this paper. The experimental procedure of this method is, firstly to release the tracer into the drilling-revealed subsurface karst cave quantitatively and place the stirring device at the tracer-releasing point to create forced convection. Then the tracer is going to diffuse to the entire space quickly. Finally to observe the tracer concentration changes of mixing center（ tracer-releasing point）and calculate the volumes of different types of caves according to different tracer concentration-time curves. This paper also presented the tracer curve generalized models of isolated l-D, 2-D and 3-D karst caves in forced convection condition, which were verified by related numerical simulation models. Isolated karst cave force convection tracer model shows that once the tracer reaches the wall of cave, it will change the speed of diffusion and affect the tracer-releasing point. The closer the wall is to the mixing center, the more obvious the turning point is. If the cave wall is close enough to the mixing center, there will be a consistency between appearance time of turning point and the time of tracer reaching the cave wall under the condition of forced convection.