输水管内水锤诱导空化流的单组分混合模型及实验研究

Water column separation is one of the key reasons causing the failure of water transmission pipeline, and the accompanied vapor cavitation and the flow field of the local water body are characteristic of obvious three-dimensional (3D) transients. This task intends to study the details and the relevant mechanism of cavitation flows induced by water column separation and rejoining in the water pipe, such as, both phase change and pressure surges, by using theoretical analysis and numerical simulation and testing techniques. Based on theoretical analysis of Rayleigh-Plesset kinetic equation for cavitation bubble, the two-phase equilibrium cavitation model is developed, and the governing equations for 3D two-phase flow mixture model together with water hammer wave velocity is established by employing single component two-phase flow mixture theory. Then the one-dimensional (1D) water hammer equations for two-phase flow mixture is deduced by analyzing the average method for physical quantities on pipe cross section, so that the researches of 1D-3D mutual numerical verification for water column separation and rejoining, and 1D-3D coupling computation mode are carried out. Aiming at the characteristics of water hammer equation and vapor volume fraction distribution for two-phase flows, efficient and accurate methods of characteristic are investigated and constructed for water hammer equation for two-phase flow, and the good calculation software for water hammer with separation, which causes vapor cavitation two-phase flows, is developed. For reservoir-pipe-valve hydraulic system, experimental observation and measurement of instantaneous hydraulic parameters, water column separation and vapor cavitation flow characteristics are carried out with the help of modern high speed photography, visual PIV (Particle Image Velocimetry) , high-precision flowmeter and pressure transducers. The rationality and reliability of above-mentioned and -related model and numerical algorithm are verified by a series of experimental data.

水柱分离-弥合水锤是导致输水管道破坏事故的主要原因之一，伴随的蒸汽空化型态和局部流场均呈现出明显的三维瞬变特征。本课题拟采用理论分析、数值模拟及测试技术，深入研究输水管内水柱分离-弥合水锤的空化相变、压力波等若干细节及机理。基于空泡Rayleigh-Plesset动力学，建立两相间平衡空化模型；采用单组分两相流理论构建含有水锤波速的三维两相流控制方程。研究管截面平均方法，构建两相流混合物模型的一维水锤方程，开展水柱分离-弥合水锤的一维-三维间的相互数值验证和耦合联合计算模式的研究。针对两相流水锤方程和汽相体积份数分布特点，研究设计两相流水锤方程高效精确特征线算法，开发伴随水锤分离的两相流水锤计算软件。借助于现代高速摄影、可视PIV、高精度流量计和压力传感器观测水库-管道-阀门水力系统的瞬时水力参数变化、水柱分离及蒸汽空化流的流动特性，通过一系列实验数据验证上述模型和算法的合理性和可靠性。

水柱分离-弥合水锤是导致输水管道破坏事故的主要原因之一，伴随的蒸汽空化型态和局部流场均呈现出明显的三维瞬变特征。基于不可压流体的弱可压缩理论，建立了有压管道瞬变流动的三维弱可压模型，三维SST k-ω湍流模型对压力衰减预测具有相对较高的精度，其流场分析表明，由关阀引起的非对称流动大约在阀前3/4倍管径距离，在压力波传播过程中，粘性耗散主要集中在粘性底层，而湍动耗散在y+=13~23时达到最大值。采用单组分两相流理论构建含了有水锤波速的三维瞬变空化流模型并捕捉到空腔演变的全过程，蒸汽穴在管长和管径方向上分布不均匀，且沿着管壁顶部方向缓慢移动。建立了一维非恒定MIAB-DGCM瞬变两相流模型，并设计开发了两相流可视化软件。基于Rayleigh-Plesset动力学方程，构建了一维两相流空化模型，并确定两种不同形式的质量输运方程的经验系数值为Singhal模型：Ce=0.02, Cc=1；Kunz模型：Cdest=1, Cprod=100000。基于瞬时壁面剪切应力，构建了准2D DGCM模型及准2D两相空化平衡模型，准二维模型预测的压力水头比一维模型更接近实验结果，对于相同的空间和时间离散，准稳态湍流假设和冷冻湍流假设的准确性随着径向扩散与压力波传播时间尺度的比值的增加而增加。开展了水锤诱导流动的一维-三维联合计算模式研究，发现适当增加耦合松弛因子和CFD每时步迭代次数有助于改善计算收敛性，同步耦合比异步耦合可靠，串行计算稳定性和准确性优于并行计算。采用高速摄影、可视PIV和高精度压力传感器等进行了水箱-管道-阀门水力系统水锤诱导空化流可视化试验，确定了不同初始流速及关阀规律对起伏管道多点空化流动瞬变特性的影响，空腔演变规律以及空腔前缘速度特性。