[关键词]
[摘要]
移动式曝气装置通过推流螺旋和曝气扰动水体掺混,提升水面温度,阻碍渠道水流结冰,可延长寒区渠道冬季输水时间。为对移动式曝气装置在明渠水环境中的运行进行计算流体动力学(computational fluid dynamics,CFD)模拟,基于固-流-热耦合模拟技术,对不同装置曝气参数和运行条件下的明渠水流物理场进行仿真分析,并对装置运行效果进行评价。结果表明:移动式曝气装置对渠道水流表层温度有一定提升作用,增加曝气速度,可以增强水体的温度掺混效果;曝气深度的增加能够扰动更深层的较高温水体,但考虑岸坡影响,推荐1.5 m深度的曝气参数;增大行走纵距可以提高影响水体范围,但会产生“低温断层区”,最优行走纵距为2 m;行进速度对温度提升影响趋势先减弱后增强,行进速度大于2 m/s时,速度越大,装置对渠道水流的扰流增温效果越好。
[Key word]
[Abstract]
Long-distance water conveyance projects are essential in solving northern China's water resource shortage problem. However, the complex water transport conditions caused by river icing in winter seriously affect the channel's water transport capacity and the project's safe operation. Balancing the safety issues with water delivery efficiency has become a significant challenge for engineering water delivery operations. Increasing the surface water temperature to delay ice formation is possible by utilizing a mobile aeration device and this ensures the safety of winter operations and enhances the water conveyance capacity of the long-distance water conveyance project. However, as an active measure to increase the winter water delivery capacity of channel engineering, its working adaptability and disturbance heating effect still lack targeted research. To reflect the changes in water characteristics under aeration operation, computational fluid dynamics numerical simulation could be used as a reliable means of fluid research. The solid-fluid-thermal coupling technology is used to simulate the rotation of spiral blades and aeration. Simultaneously considering the heat exchange between water and atmosphere, the changes in water temperature caused by changes in the flow field are calculated. During the simulation, overlapping grid technology is introduced to optimize the dynamic grid calculation, ensuring computational efficiency and accuracy. The initial velocity distribution, temperature distribution, device operating speed, and operating path of the fluid through user-defined functions are set. Two different calculation schemes are designed to simulate and analyze the water characteristics under different aeration speeds, aeration depths, longitudinal distances, and walking speeds. The average temperature change curve and the average water surface temperature distribution map are drawn. The changes in water characteristics under different device parameters are changed and flow operating conditions are pushed, providing a basis for device parameters and operational design. The results are as follows: (1) Increasing the aeration rate within the safe allowable range can enhance the mixing effect of water. The aeration rate characterizes the size of the aeration amount. A higher aeration rate results in more significant disturbance to the water body and a higher increase in water surface temperature. (2) The aeration depth can increase the upper limit of temperature increase. A higher deep-water temperature can cause a greater temperature to increase as well. The disturbance caused by deeper aeration has a greater resistance to water pressure. In the case of insufficient aeration, the disturbance caused by deep aeration will gradually flatten with the upward migration of water flow. Considering the influence of slope, a depth of 1.5 m is recommended as the appropriate device parameter. (3) The optimal walking distance for operation is 2 m. Expanding the distance can increase the range of disturbed water surface, and secondary mixing will be carried out in local areas to increase water surface temperature. However, excessive longitudinal distance can lead to the appearance of low-temperature fault zones, which is not conducive to improving the efficiency of turbulent flow heating. (4) The trend of the effect of walking speed on temperature increases first weakens and then strengthens. When the speed is less than 2 m/s, the slower walking speed results in higher local aeration and a more substantial temperature mixing effect. After the speed exceeds 2 m/s, the acceleration of the speed causes the device to undergo secondary disturbance on the walking path. The improvement of the warming effect is more significant than the weakening effect caused by the reduction of local aeration.
[中图分类号]
[基金项目]