| Ice is commonly found in rivers in northern China in winter,and ice formation is easy to occur during freezing and thawing periods.The formation of ice cover not only inhibits the photosynthesis of plants and microorganisms in the water body,but also reduces the water flow along the path,which leads to the water anoxia,but also reduces the water transport capacity of the river.The channel section is mostly complex compound section.No matter the flood period or the ice condition,the flow pattern of the river is more complex than that of the single section open channel,and the aeration helps to solve the problem of water anoxia,and the influence of aeration on the water transport capacity of the channel under the ice cover is also needed.The hydraulic characteristics of aerated flow without ice cover are particularly necessary.In this paper,air compressor and hose are used as aerator to aerate the flow of water,and the foam float cap is used to simulate the ice cover.The distribution of flow velocity and air concentration along the horizontal,vertical and vertical distribution under the condition of complete float cover and no float is studied under the condition of different flow and air blowholes.The theoretical basis is provided for ice disaster prevention,water ecological safety in winter and winter water conveyance strategy.The conclusion is that only when the main channel is overflowing,the velocity of the main channel increases first and then decreases along the transverse direction,and the maximum velocity reaches the middle point of the main trough.When the flow of water floodplain,the flow of Q is relatively small,the water flow in the beach is between the side wall and the main water wall of the main trough.It is driven mainly by the main channel water body,which is less influenced by the potential energy and the side wall.The nearer the boundary wall is,the nearer the boundary wall is,the more the flow Q increases,the influence of the potential energy on the tidal flat gradually becomes the largest.At the same time,the flow turbulence at the junction of the side wall,the beach and the main channel increased,making the velocity of the beach increase first and then decrease along the horizontal direction,and the maximum value approaches the midpoint of the beach.Under the influence of gas acceleration and turbulent flow at the junction of the channel and the trough,the velocity of the channel increases first and then decreases along the vertical direction.The flow velocity decreases,but the flow velocity distribution is not obvious and the maximum value of the vertical distribution of flow velocity is not obvious.Gas can reduce the contact area between the floating cover and the water surface,which is beneficial to the water transport.A part of the gas emitted from the air blowhole is dissolved in the water body,and the other is in the form of bubbles in the water body,and is constantly exchanging gas with the surrounding water body.Because of the smooth flow,most of the gas floats,and only a small amount of gas spreads to the side wall in the form of tiny bubbles and moves longer.Because of the large friction of the channel corner and the strong turbulence of the flow,the concentration of the micro bubbles makes the aeration concentration larger.After the increase of floating cover,there are two reasons for the decrease of air concentration at the bottom of the 1-3 air blowholes and under the dense air hole.The first is the rise of the water level in the floating cover,the greater of the pressure at the bottom,the greater of the gas solubility,and the two is the enhancement of the turbulence and the distribution of the concentration of aeration.Due to the collection of small bubbles and the movement of the floating cover wall,the aeration density of the flow surface increases under the dense porosity. |
