大扩散角明渠水流特性及其调控措施研究

发布时间：2018-06-16 20:55

本文选题：大扩散角明渠段 + 水流特性　；参考：《华北水利水电大学》2017年硕士论文

【摘要】：在实际工程中,受限于场地不足,在洞、渠结合部往往无法布置足够长的明渠扩散过渡段,不得不采用大扩散角的扩散段来实现水流衔接。但是在此类的扩散段中,由于受边界条件影响,水流在扩散段中扩散不充分,导致断面能量分布不均,边界层分离,在经过扩散段时水流会出现主流偏移的现象,形成大范围的回流区及漩涡。这种不良流态会影响渠道的正常运用,极大地限制了输水明渠扩散段的使用条件;为了要实现扩散段的水流平顺均衡过渡,必须了解其水流特性并相应采取有效的调控措施。本文试图通过系列水力模拟进行扩散段水流特性及调控措施的试验研究,主要借助两个扩散段水槽模型,研究随流量和扩散角改变,水流经过扩散段时的水力要素变化特征;根据大扩散角明渠的水力特性提出用以调控水流的构筑物形式,验证并优化潜没式三角翼体的调控效果。在明渠扩散段无调控措施情况下,测量了扩散段特征断面水深、流速等水力要素,通过施放示踪剂观测了扩散段及其连接段的水流流态;分析研究了扩散段水力要素的空间分布特性,扩散段内的边界层分离情况,水流经过扩散段的能量损失,以及边界条件改变对扩散段及其连接段水流流态的影响。研究发现当扩散段扩散角在大于8°时,水流产生边界层分离所形成的回流、漩涡相对较小,但水流稳定性较差,主流易产生随机性偏移现象。随着扩散角的加大,水流形成回流漩涡的范围及强度亦增大,扩散段特征断面流速分布越发不均匀,能量损失增加,过流能力降低。当扩散角增大到45°时,扩散段两侧的回流区产生较强的剪切挤压作用抑制水流横向扩散,也抑制主流的随机偏移,水流非稳定性又受到一定抑制。明渠扩散水流下游断面的过流条件与扩散段水流状态有一定的响应关系,改变下游断面过流条件,扩散段主流的偏移状态及下游连接段回流区的形态也随之改变。根据大扩散角情况下明渠水流特性,采取底部介入式调控水流方法,提出了一种适用于调控大扩散角水流流态的潜没式三角翼体,研究了该措施的导流机理。试验表明,三角翼体通过前端攻角对水流的分流与两侧翼板的导流作用,强化水流横向扩散运动,改善了水流动量的横向分布形态,增强了扩散段水流结构的稳定性,使水流经过扩散段时能够较为均匀地扩散到整个过流断面,扩散段及其连接段流态得到改善。
[Abstract]:In the actual engineering, limited by the shortage of the site, in the tunnel, the junction of the canal often can not arrange a long enough open channel diffusion transition section, so the diffusion section with a large diffusion angle has to be used to achieve water flow connection. However, in this kind of diffusion section, due to the influence of boundary conditions, the diffusion of water in the diffusion section is not sufficient, which leads to the uneven distribution of cross-section energy, the separation of boundary layer, and the phenomenon of mainstream migration when the flow passes through the diffusion section. Form a wide range of backflow zones and whirlpools. This kind of bad flow state will affect the normal operation of the channel and greatly limit the use conditions of the diffusion section of the open channel, in order to realize the smooth and balanced transition of the flow in the diffusion section, it is necessary to understand its flow characteristics and take effective control measures accordingly. In this paper, a series of hydraulic simulation is used to study the flow characteristics and control measures of the diffusion section, mainly by means of two flume models of the diffusion section, to study the characteristics of the hydraulic factors changing with the change of the flow rate and the diffusion angle, and when the flow passes through the diffusion section. According to the hydraulic characteristics of the open channel with large diffusion angle, the structure form used to control the flow of water was put forward to verify and optimize the control effect of the submerged delta wing. In the case of no control measures in the open channel diffusion section, the hydraulic factors such as water depth and velocity of the characteristic section of the diffusion section are measured, and the flow patterns of the diffusion section and its connecting section are observed by the application of tracer. The spatial distribution characteristics of hydraulic elements in diffusion section, the separation of boundary layer in diffusion section, the energy loss of water flow through diffusion section, and the influence of the change of boundary conditions on the water flow state of diffusion section and its connection section are analyzed and studied. It is found that when the diffusion angle of the diffusion section is greater than 8 掳, the reflux formed by the separation of the boundary layer is produced. The swirl is relatively small, but the stability of the flow is poor, and the main stream is prone to the phenomenon of random migration. With the increase of diffusion angle, the range and intensity of reflux vortex are increased, the velocity distribution of the characteristic section of diffusion section is more and more uneven, the energy loss increases, and the overcurrent capacity decreases. When the diffusion angle is increased to 45 掳, a strong shearing and squeezing action is produced in the circumfluence zone on both sides of the diffusion section to restrain the lateral diffusion of the flow and the random migration of the main stream, and the instability of the flow is restrained to a certain extent. There is a certain response relationship between the cross flow condition of the downstream section of the open channel diffusion flow and the flow state of the diffusion section. When the flow condition of the downstream section is changed, the migration state of the main stream of the diffusion section and the form of the backflow zone of the downstream connecting section also change. According to the characteristics of open channel flow under the condition of large diffusion angle, a submersible delta wing body suitable for regulating the flow state of large diffusive angle water flow is proposed by adopting the method of bottom interventional control. The mechanism of this method is studied. The experimental results show that the delta wing body distributes the water flow through the angle of attack at the front end, strengthens the lateral diffusion movement of the water flow, improves the transverse distribution of the water flow momentum, and enhances the stability of the water flow structure in the diffusion section. When the flow passes through the diffusion section, the flow pattern of the diffusion section and its connection section can be improved.
【学位授予单位】：华北水利水电大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TV133

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