【作者】 王海云；

【导师】 戴光清；

【作者基本信息】 四川大学 ， 水力学及河流动力学， 2004， 硕士

【摘要】 工程实际中常将导流洞改建为泄洪洞,洞首多采用龙抬头段与原导流洞相连结。龙抬头泄洪洞泄洪时通常形成的是明流流态,其突出的特点是:流速高、单宽流量大、低数和小底坡,反弧末端掺气坎后射流的重力影响十分显著,掺气坎后底空腔区流线弯曲严重,掺气空腔内容易产生积水等。国内外学者对高水头泄洪洞掺气设施的体型优化,进行了较多的试验与理论研究;然而,多数文献在提高掺气设施的掺气性能方面,仅考虑了沿顺水流方向的二维变化,所提出的掺气设施存在体型复杂、不容易施工或施工难度大等问题,掺气坎后水流存在垂直于水流方向的横向流动,进而影响了掺气效果。本文首先通过试验研究,从掺气坎后空腔区的三维形态考虑,提出了一种新型V型槽式掺气坎(简称V型坎);其主要特点是:掺气坎后射流水舌沿垂直于水流方向的重力分布发生变化,即掺气坎后射流水舌的流速、挑角和高程,沿中心向两侧保持连续变化,其水舌落水点的范围即空腔长度,成为一连续变化的曲线,而且沿曲线处水流的流速也是连续变化的,从而减弱或消除了水流落水处由碰撞形成回水。在V型坎出口断面处,水流的三维扩散更充分,水舌与空腔的接触面明显增大,有利于增加水流的掺气量,同时在落水点处受水流的强烈紊动,进一步提高了掺气效果,对底空腔长度、通气量等掺气特性指标都有明显的改善。通过对试验结果的比较和分析研究,在前人研究基础上,建立了预测V型坎掺气特性的数学模型,提出了有关底空腔长度、空腔负压、通气量的理论预测公式。 <WP=4>为了对龙抬头明流泄洪洞水流流场特性进行全面深入的研究,本文还采用三维双方程紊流模型模拟了泄洪洞的紊流流场,并且采用非结构网格来处理复杂的边界形状,对自由水面,引入水-气两相分层流理论中的流体体积分数法(VOF)来迭代求解。通过模拟计算,得到泄洪洞内水面线、速度场、压力场和底空腔长度等水力参数,通过与实测结果对比分析,数值模拟结果与实测值吻合较好。由于泄洪洞反弧段下游水流表面自掺气尚不够充分,底部强迫掺气尚未充分扩散,在反弧段下游侧墙,容易形成较大范围的清水带(掺气盲区),同时受反弧段离心力和掺气坎后侧墙存在低压区的影响,故下游侧墙壁面易发生空蚀破坏。文中在反弧末端设置了突缩和突跌掺气设施,在侧墙两边对称布置侧向折流器;试验结果表明,侧墙突缩比的范围宜为0.012～0.018,侧收缩坡度范围在1:40～1:20之间。加设侧向折流器后,侧墙水流的出射角增大,侧空腔畅通,并直接和底空腔相连,形成稳定的侧空腔和底空腔,更有助于掺气坎后水舌的全断面的掺气,对侧墙和底板皆起到了很好的保护作用。更多还原

【Abstract】 In the hydraulic engineering diversion tunnel is often rebuilt to flood spillway tunnel,which linked dragon-raise-head sector to the diversion tunnel. The aerators are widely used in flood spillways tunnels to prevent the cavitation damage of the structures. The characteristics of the dragon-raise-head spillway tunnel are high head, large-unit-discharge, low Froude number and slight slope. Large-discharge and low Froude number imply high depth of water,the impact of the gravitations is notable. So there is easily backwater in the air chamber,which obviously affects on the hydraulic character of the aerator. On the condition of slight slope flows the bottom of air chamber tends to cause backwater flow and obstruct air current. In the view of research on configuration optimization of aeration device of the free flow spillway tunnel former scholars emphasis on two-dimension research,i.e. following flows direction variability and ignore the flows crossing run of vertical water direction. So for this flow condition the common aeration device doesn’t meet the demand of protecting cavitation damage.A new V-type aerator, the three dimensional aerator has been put forward through model test. The main characteristic is that gravitations distribution of free jet nappe alternates not only in the directions of longitudinal and vertical, but also in the cross direction along vertical flowing direction. The velocity,jet-trajectory <WP=6>angle and water depth change lineally from the center to both sides. The range of downstream edge is continuous curvilinear. Thus backwater in the air chamber is eliminated. The reason of why the V-type is better has been analyzed theoretically. For this type, on the outlet of free jet the three-dimensional flow diffusion is more sufficiency than the traditional two-dimensional aerator. Therefore the air entrainment rate is larger, the length of air chamber is longer. It is mainly because that, the length of the air chamber is continuously varying along the lateral direction within a range and along downstream bilateral edge strong turbulence fluctuation further contributes to aerated capacity. Based on model experiment, numerical model for V-type aerator is built and theory formulas are put forward on the length and pressure of air chamber and air discharge. In order to study the hydraulic characteristics of the aeration device comprehensively the method of turbulence numerical simulation is used to study the free flow spillway tunnel. The fractional volume of fluid (VOF) model of the air-water two phase flow is introduced to the three-dimensional k-εtwo–equation turbulence model and combined with the geometry reconstruction scheme to solve the free water surface. The unstructured grid is used to treat the irregular boundary. By these methods, the turbulence flow field of the free flow spillway tunnel is simulated successfully. The free water surface and the distribution of velocity and pressure on the free flow spillway tunnel are obtained by the turbulence numerical simulation, which are analyzed and compared with the test results, and agreed well with each other.Behind the aerator of the anti-arc bottom self-aerated is not enough at the surface of flow and the aeration by force is not sufficiently diffuse,which causes a large un-airflow area in the sidewalls, at the same time influenced by centrifugal force and low pressure areas of sidewalls——all of these as we know it is easy to be destroyed by the cavitation under these conditions. In this paper an aerator with a sudden contraction and a vertical drop is used to bottom of anti-arc. The results of model tests indicate the sudden contraction ratio is suitable to 0.012~0.018 and grade of slope should be 1:40~1:20. The air entrainment quantity is obviously <WP=7>affected by lateral deflector. The lateral air chamber is an important aeration mechanism when the lateral air chamber is connected to the bottom cavity,which prevent cavitation damage of sidewalls and soleplates effectively.更多还原