Experiment Study On Ice Cover Formation Process Of Compound Section Channel In Cold Region

China has a large area but uneven distribution of resources.With the rapid development of economy and society,the development of large-scale water distribution project and water transfer project,which is the lifeline project for optimal allocation of water resources in the cold regions of northern China,is very fast.And the demand for water transportation in winter is also increasing.Project practice shows that the compound section channel in the cold regions cannot only adapt to the demand of large changes in water flow in winter and summer,but also conducive to heat preservation and water transfer by narrowing the water surface in winter.But there are few research about the ice cover formation process and the ice cover water delivery operation process of compound section channel.The research is such that it is impossible to theoretically analyze the problem of ice cover water transfer in the compound section channel.Therefore,this paper conducts experimental research on the ice cover formation process and the ice cover water delivery operation process in the hydraulic low temperature simulation laboratory with the compound section channel as the research object,and then compares with the ice cover formation process of the trapezoidal section channel.At the end,Combined with numerical simulation,the surface velocity of the compound section channel and the trapezoidal section channel and the influence of ice cover development on the flow velocity and heat transfer coefficient were analyzed.The main research contents and achievements are as follows:(1)A set of research methods and test methods for the study of channel ice cover formation considering hydraulics,thermodynamics,meteorology and channel geometric boundary characteristics are designed.(2)According to the test data analysis,under the same flow conditions,compared with the trapezoidal section channel,the compound section channel has the characteristics that the shore ice is formed faster and thicker,and the ice cover of the middle main part is formed slowly.Compared with the trapezoidal section channel,it is more likely to generate stable and firm shore ice,and it can also extend the water delivery time of the main channel in winter.(3)The direct calculation formula of the thickness of the channel static ice cover is given by the relationship between the thickness of the ice cover and the accumulated hourly negative temperature;Based on the Stefan degree-day method,the direct calculation formula of the thickness of the moving ice and static ice cover of the channel is also given;At the end,the formula for calculating the channel shore ice increment is determined by the experiment data.(4)Through the experiment of the ice cover water transfer operation on the compound section channel,it can be known that the small flow condition back to the main tank water transfer can delay the development of the ice cover in the main tank and promote the winter water transfer under the joint heat preservation effect of the ice cover and the middle air layer.The time and thickness of the intermediate insulation layer have a large effect on the growth of the ice cover in the main tank.On the basis of analyzing the growth mechanism of ice cover thickness,considering the factors such as ice cover heat preservation,middle air layer heat preservation and water level decrease,the ice cover water freezing degree-day method is proposed according to the thermodynamic theory.(5)Combined with numerical simulation analysis,it can be seen that under the same flow conditions,the surface velocity of the beach part of the compound section channel is smaller than the surface velocity of the trapezoidal section channel,while the surface velocity of the main section of the compound section is larger than the surface velocity of the trapezoidal section;In the case where the compound section only passes the water in the main tank,the surface velocity of the main tank is greater than the surface velocity of the trapezoidal section channel.The thickness of the ice cover on the compound section and the development speed of the shore ice are affected by surface flow velocity and heat exchange.In summary,the compound section channel can generate a stable and safe thicker ice cover under the same thermal and hydraulic conditions than the trapezoidal section channel;While in the width of the ice cover,the compound section develops slower than the trapezoidal section.Considering that the winter flow condition is small,the compound section channel always uses the main tank to transport water.The narrow-deep main tank is difficult to freeze the surface water compared to the trapezoidal section.Therefore,after the ice cover is generated on the beach by controlling the water level,the water level is lowered by the main tank to carry out the ice cover.The research results will provide a theoretical basis for the existing compound section channel ice cover water delivery problem,and help solve the problem of winter water delivery difficulties in the cold regions of northern China.