水库水温分层的流场分析

水库水温分层是流体密度流现象的一种,其形成受库区内流场、太阳辐射和表层热交换的共同影响,而水温分层状态的出现又将影响水库来流在库区的流动过程和出库水流的温度.以流场与温度场耦合计算的立面二维水库水温模型为基础,对水温分层的主要影响因素进行了理论分析,结合数值模拟讨论了温度场与流场的相互作用,对分层状态与来流发展特别是与垂向流动的关系进行了剖析.认为一定的来流水温差和表层热通量是水库形成分层状态的必要条件;水库表层温跃层对紊动扩散的抑制使温跃层内纵向和垂向动量均低于层外水体,上游来流高温水遇此温跃层之后易被阻碍而形成密度流下潜;双温跃层主要由高温流动层通过紊动不完全侵蚀底部低温水层而形成;水库底部回流区方向受主流动层流线方向控制并随主流动层流线趋于水平而被压缩;泄流孔口高程处主流动层形成的流速切应变使附近温度梯度减小,等温线趋于稀疏,主流动层随流量增加而增厚.

Flow Field of Thermally Stratified Reservoir

Reservoir thermal stratification is a phenomenon of density current, whose formation is influenced by combined factors, including flow field, solar radiation and heat exchanges. The thermal stratification will affect the flow process of incoming flow in reservoir area and the temperature of outgoing flow. Based on the laterally-averaged reservoir water temperature model, which was obtained by the coupling computation of flow field and temperature field, this paper made a theoretical analysis of the main factors influencing thermal stratification. Furthermore, it discussed the interaction between temperature field and flow field by the numerical simulation method. In addition, it explored the relationship between stratification and the trend of incoming flow, especially the flow in the vertical direction. This paper concludes that the stratification can only be formed under necessary conditions, which are a certain cooling range of incoming flow and the heat flux on surface; due to the inhibition effect of thermocline on turbulent diffusion, the longitudinal and vertical momentums in thermocline are both below that of the water body outside the thermocline. The high-temperature incoming water upstream, when encounting this thermocline, will be easily hindered. Then, it forms a density current and dives to the bottom; through the incomplete erosion of low-temperature water layer at bottom by high-temperature fluidized bed, which is mainly caused by turbulence, a duplex thermocline will be formed; the direction of circumfluence field at bottom is controlled by the flow direction of the flowing layer of the main stream, with which its direction tends to become horizontal and then get compressed; the shear strain of flow velocity, produced on the flowing layer of the main stream, at the location of the orifice of flow discharge in height, makes the temperature gradient nearby decrease, the isothermal line distribute sparsely, and the movable layer of the main stream thicken with the increase of flow.