Physical Model Test And Determination Of Key Parameters Of River Anchor Ice Evolution

Heilongjiang River Basin is located in the northeast of China,which has the lowest annual average temperature in China.The negative temperature month of the whole year is nearly six months.Ice jam,shore ice and anchor ice often appear in Heilongjiang Basin in winter.The process of river ice production and dissipation will disturb the surrounding agricultural engineering and ecological environment.The growth and release process of anchor ice will affect the operation of hydropower station,ice traffic,water ecosystem and sediment transport.Based on the physical model test conducted in the low temperature environment simulation laboratory,the evolution process of river anchor ice and its main influencing parameters are preliminarily explored in this study.The conclusion is as follows:(1)In all the model tests of anchor ice evolution,the shape of anchor ice starts from the adhesion of psoriasis ice.On the pebble at the bottom of the flume,the anchor ice grows in two different positions,namely the front formation and the back formation.The main observation in this study is the front formation.After the formation of the anchor ice,it began to grow in the fr ont gap of the pebble.The anchor ice first grew to the upstream and the water surface.Because the growth of the anchor ice exceeded the top of the pebble particles,it began to flatten and grow to the downstream under the influence of the water flow,which led to the generation of the ice tail.Generally,after the formation of an ice tail,the other ice tail will start to grow downstream from the left and right of the previous ice tail,and this growth form will continue to grow downstream until the bottom of the tank is completely covered.(2)The release of anchor ice observed is due to the action of current scour and buoyancy.By comparing the bottom roughness of three different flumes,it is found that the anchor ice with small roughness is easier to release than that with large roughness.This is because the cohesive force between the gravel with small particle size and the anchor ice is not enough,and it is easy to be washed away by water.(3)The thermal growth of anchor ice was found through the water temperature curve during the experiment.According to the temperature curve of water temperature recorded in the experiment,it is found that there is a thermodynamic process during the experiment:when the water flow is too cold,debris ice appears in the water,the turbulent flow mixed with debris ice particles to bring it to the bottom of the tank,some debris ice particles adhere to the bottom of the tank to form anchor ice.When the latent heat released by the formation of anchor ice and debris ice is not enough to balance the heat loss on the surface of the water,the subcooling of the water continues to increase.When the released latent heat is balanced with the heat loss on the surface,the water temperature will no longer drop to the minimum temperature.Large amounts of anchor ice rapidly formed and grew during this period,and the water temperature began to rise slowly due to the increase of latent heat released by the massive growth of anchor ice.As the surface ice is regularly removed and skimmed,the heat exchange process of water and gas continues.Each time the surface ice is removed,the latent heat released by the anchor ice and debris ice in the tank is not enough to balance the heat lost by the water,making the water temperature dro p again.At the later stage of the experiment,no new debris ice was produced in the water,and the water temperature remained basically constant.(4)The density and porosity of anchor ice were measured.It was found that the density of anchor ice increased with the increase of Froude number Fr and Reynolds number Re,and the porosity of anchor ice decreased with the increase of rough Reynolds number Re*.(5)The influence of the evolution of the anchor ice on the hydraulic resistance is studied by changing the roughness of the bottom of the flume.In the early stage of the evolution of the anchor ice,the growth of the anchor ice increased the roughness of the bottom of the flume.As the roughness reached the peak,the test continued,the riverbed was completely covered by the anchor ice,and the roughness of the riverbed surface gradually decreased.The growth rate of the relative roughness curve under different temperature conditions is obviously different.The relative roughness curve with lower temperature obviously grows faster,but its growth rate decreases with time.When the temperature is-20?,the values of the roughness n and the relative roughness n~*on the bottom of the flume are the largest;the growth rate of the roughness n under different velocity conditions is obviously different,and the roughness of the test group with 0.25 m/s velocity is increased With the increase of Froude number Fr and Reynolds number Re,the average relative roughness n~*began to decrease.(6)According to the thickness curve of anchor ice,the growth rate curve of anchor ice is obtained.The thickness curve and growth rate curve of anchor ice are obviously different under different air temperature conditions.When the air temperature is-20?,the growth of anchor ice is the fastest,and the time required for the growth rate to reach the peak value is the shortest;when the roughness of the bottom of the water tank is 0.5 cm,1 cm,2 cm,the thickness of anchor ice is the largest in the test group with the roughness of the bottom of the water tank of 1 cm,and when the roughness of the bottom of the water tank is 0.5 cm,the growth of anchor ice is the shortest The maximum speed peak and the shortest time to reach the peak value;three groups of different Froude numbers were used to study,and it was found that the thickness and growth rate of the experimental group with Froude number of 0.56 at the initial stage of the growth of the anchor ice were the largest,and the thickness and growth rate of the experimental group with Froude number of 0.25 were the largest as the experiment continued.