冰封期天然弯道水流运动结构研究

The cross section configuration of natural curved reach always is complicated and changeful. Flow from open to enclosing undercurrent in ice-cover season, and the existing additional ice lead to bend flow influenced by the riverbed and ice cover. The flow structure is significantly changed, at the same time reduce the capacity of transmitting ice and ice flow, easy to jam ice freezing and bring ice flood disaster. The research on flow structure of natural curved reach redistribution with the ice cover progression is deficient currently. Therefore, this project intends to use a method which combines field prototype test with mathematic model, taking the natural curved of Inner-Mongolia Toudaoguai reach as the research object, collecting the three-dimensional flow field during open river period of curved reach, meteorological, the thermodynamic, ice thickness, ice temperature, water level under ice data. The research analyze effect of additional ice cover on natural curved reach flow structure, study the relationship between ice friction and meteorological, thermodynamics, ice cover growth and decay, establish three-dimensional mathematical model of curve reach flow in ice cover period and simulate the redistribution law of flow structure in different development stage of ice cover. The research results will further enrich the hydrodynamic basic theory of natural curved reach in frozen period, which provide hydrodynamic technology supporting for studying the formation and dynamic evolution of ice cover, ice jam and ice dam in natural river, and both academic significance and practical value for promoting the development of river ice engineering research.

天然弯道断面形态复杂多变，在封冰期，水流从明流转变为封闭的暗流，附加冰盖的存在使弯道水流受河床和冰盖共同作用，显著改变水流流动结构，降低弯道输冰能力和冰下过流能力，易于卡冰封河，引发冰凌灾害。目前针对天然弯道水流运动结构随冰盖发展重分布的研究成果较少。因此，本项目拟采用野外原型测验与数学模型计算相结合的手段，以黄河内蒙古头道拐段天然弯道为研究对象，采集畅流期弯道三维流场，封河期气象、热力学资料与冰厚、冰温、冰下水位、冰下流场等数据。分析附加冰盖对天然弯道水流运动结构的影响；研究冰盖摩擦力与冰盖生消的关系，建立冰封期弯道水流运动三维数学模型，模拟天然弯道冰盖的不同发展阶段水流运动结构重分布规律。项目研究成果将进一步丰富天然河流弯道水动力学的基本理论，为研究天然河道冰盖、冰塞及冰坝的形成和动态演变提供水动力学方面的技术支撑，促进河流涉冰工程研究发展，具有重要的学术意义和实用价值。

天然弯道河段易于发生首封，其断面形态多复杂多变，在封冰期，水流从明流转变为封闭的暗流，附加冰盖的存在使弯道水流受河床和冰盖共同作用，显著改变水流流动结构，降低弯道输冰能力和冰下过流能力，易于卡冰封河，引发冰凌灾害。项目以黄河内蒙古河段什四份子弯道为研究对象，开展封河前后原型测验。在畅流期，采用走航式H-ADCP进行弯道地形及三维流场测验；在稳定封河期，开展了研究弯道冰层厚度、冰下水位、冰温等冰情资料原型测验；同时建立了冰封期弯道水流运动的三维紊流数学模型，开展了冰下过流能力研究。研究结果表明：（1）畅流期，水流在通过弯道段时由于水流离心力作用凹岸水面高于凸岸水面，水面即有从凸岸向凹岸倾斜的横比降出现，水面比降约为2.68‱。（2）在畅流期表层流速最大，随水深的变大流速逐渐变小。（3）稳定封河期，弯道的上游水深小于弯道下游水深，弯道的上游冰厚要小于弯道下游冰厚，弯道上下游流速大小变化不大。（4）冰盖的存在，加大了湿周，增加了冰盖底面与水流间的阻力，贴近冰盖底面的流速趋于零，断面上的最大流速区下移。沿河宽方向在冰面以下0.5m和河床以上0.5m均表现为在凹岸流速大于凸岸，冰下0.5m处流速大于河床0.5m以上流速。（5）考虑冰花堆积影响，冰盖形成初期初始冰盖糙率n初一般为0.050～0.055，稳定封河后期冰盖糙率n末一般采用0.013～0.017。（6）模型计算表明，稳定封河期比畅流期水位高1.5m左右，结合冰盖糙率的取值，提出封河期与畅流期之间水位关系式。项目研究成果进一步丰富了天然河流弯道水动力学的基本理论，为研究天然河道初始冰盖的形成和动态演变提供水动力学方面的技术支撑，促进了河流涉冰工程研究发展，具有重要的学术意义和实用价值。