浅层地温场中热对流数值模拟

温度示踪的研究区域大多在地表浅层，浅层地温场主要受气象和水文影响。气温波动可用傅立叶级数精确表示，由此建立了在表层气温和垂向水流共同影响下的浅层地温场瞬态分析模型，用Laplace变换的方法得到其解析解，并用有限元模拟了垂向水流对浅层地温的影响。模拟结果表明：浅层地温有季节波动，在地下水补给区，气温波动振幅衰减速率明显减缓，表现为表层气温波动可以影响到更深的深度；在排泄区，温度波振幅衰减很快。另外，还模拟了水平集中渗漏带附近的瞬态温度场，发现由于热对流的传热能力远大于热传导，强渗漏带温度迅速与补给源温度相一致，温深剖面出现异常，温度异常带形成后，继而通过热传导改变较大范围内地质体热量分布。离低温补给源越近，地质体降温越快，温度改变越多；反之则越慢，温度改变越少。因此，由温深剖面的温度异常，可精确探查渗漏带位置。

Numerical simulation of thermal convection in shallow ground temperature field

The study areas of temperature tracer method are mostly concerned with shallow layer, its temperature is mainly influenced by weather and groundwater. Fluctuation of air temperature can be accurately expressed by Fourier series. How surface temperature and vertical groundwater flow influencing temperature field were demonstrated with a transient analysis model. The analytical solution is obtained by Laplace transform and numerical solution by FEM. The results indicate that shallow ground temperature field also has seasonal fluctuation; but the decay rate of amplitude mitigates singnificantly; and fluctuation of air temperature can influence deeper in groundwater recharge district: while in discharge district, amplitude of temperature waves decays faster. Besides, a transient temperature field near horizontal strong leakage layer is simulated. It is found that because heat transfer ability of convection is much stronger than conduction, the temperature within strong leakage zone is consistent with recharge source quickly and then temperature field in a wider range is changed by conduction. Geologic bodies near low temperature source are cooled faster and changed more, vice versa, slower and less. Therefore, the potential leakage zone can be traced accurately in this way.