【作者】 李晓鹏；

【导师】 董志勇；

【作者基本信息】 浙江工业大学 ， 市政工程， 2009， 硕士

【摘要】 在高坝泄水建筑物中会遇到常见的高速水流问题,如空化空蚀、掺气、脉动振动、消能防冲等。尤其在溢流坝、泄洪洞、陡槽等泄洪建筑物中,当水流速度达到一定程度时,水流压强低于相应的饱和蒸汽压强,产生空化现象。空穴流由低压区流到压力升高区便会产生空蚀破坏。当空化现象不可避免时,为了减免高速水流空化产生的空蚀破坏,经济而有效的措施是在低压空化区或在易发生空蚀部位上游设置掺气设施强迫掺气。在泄水建筑物施工中,过流壁面常会形成圆柱形突体、升坎、跌坎、凹槽、三角形突体及蜂窝等不平整突体。泄水建筑物的运行实践表明,即使过流壁面上仅残留几毫米的不平整突体,亦会引起砼表面大范围的空蚀破坏。首先,本文针对突体引发空化现象的国内外研究现状和发展动态作了比较全面的回顾;其次,本文重点对由圆柱形突体引发空化的水力特性进行探讨,在直流式水洞中利用三维粒子图像测速仪(PIV)对其进行了初步试验研究,通过测量两种不同高度不锈钢试件在不同掺气浓度条件下空化区的流速分布,探讨掺气量与速度场分布的关系;最后,本文针对泄水建筑物过流壁面中的圆柱形突体周围流场进行数值模拟,模拟不同高度圆柱形突体以及不同掺气浓度对空化区域内流动特性的影响,给出瞬时流速场和压力场,并与PIV实测结果进行了比较,结果表明,数值模拟与实测值总体上吻合较好,能较好地模拟因表面圆柱形突体引发的空化现象。更多还原

【Abstract】 Some problems of high-velocity flow are often encountered when released from these high dams, such as cavitation, aeration, fluctuation, vibration, energy dissipation etc. Especially in spillway dams, spillway tunnels and chute spillways of high-head discharge structures, cavitation phenomena will occur while flow velocity reaches a certain value and flow pressure is lower than the relevant saturated vapor pressure. Cavitation erosion arises from the cavity flow from underpressure to higher pressure. As cavitation phenomenon is inevitable, in order to prevent the erosion due to the cavitation in high-velocity flow, an economic and effective measure is to set up aerators for generating forced aeration in underpressure cavitation regions or upper locations liable to cavitation erosion. Surface irregularities such as offset into flow, offset away from flow, cylindrical protrusion, and triangular protrusion on the surface usually exist under the construction of outlet works. The operation practice of outlet works showed that large-scale cavitation damage would occur even if there existed a slight surface irregularity of only a few millimeters on the overflow surface. Firstly, a comprehensive review and a progress in cavitation characteristics of high velocity flow over a surface cylindrical protrusion; Secondly, Three-dimensional Particle Image Velocimetry has been used to study the flow field of high-velocity flows over surface irregularity—cylindrical protrusions. By measuring the flow velocity distribution over two different heights of stainless steel specimens in cavitation region with different air concentrations, the relation between entrained air rate and flow velocity was investigated. Finally, this thesis presents numerical simulation of both horizontal and vertical two-dimensional flow fields around cylindrical protrusions on overflow surface of flood release structures. Effects of cylindrical protrusions with different heights and different air concentrations on flow characteristics in cavitation region were considered. Velocity and pressure profiles in horizontal and vertical two-dimensional flows were obtained, and a comparison with the PIV measured data was made. The results showed that numerical simulation reasonably agree well with experimental data.更多还原