黏弹性管道中气液两相瞬变流实验及模型

为了给管道安全设计提供建议,以及使基于瞬变流理论的管道故障检测技术在黏弹性输水管道中得以应用,对黏弹性管道中气液两相瞬变流进行研究.首先,在重力流有机玻璃管道中进行快关阀气液两相瞬变流实验.其次,以离散蒸汽空腔模型(DVCM)和离散气体空腔模型(DGCM)为基础,用体积含气率对瞬变流波速进行修正,建立两个将非稳定摩阻和管壁黏弹性影响考虑在内的一维气液两相瞬变流模型.实验和模型结果表明:在初始流型为泡状流的低压系统中,DVCM能准确模拟实验波速,而DGCM求得的平均波速值比实验波速大.在模拟初始流型为泡状流的瞬变流时,DVCM模拟结果与实验值吻合得很好,而DGCM模拟结果的最大峰值更大,对管道设计来讲更为安全;在气液两相瞬变流过程中,气体的可压缩性使得管壁的黏弹性效应对压力的衰减作用大为削弱,导致非稳定摩阻的影响不可忽略,且由于气体存在使得整个瞬变流过程中压力衰减变慢.

Experimental and modeling study on gas-liquid two-phase transient flow in viscoelastic pipes

To make suggestions on the pipeline safety design and apply the transient-based technique into the fault detection in the viscoelastic pipeline, this paper studies the gas-liquid two-phase transient flow in the viscoelastic pipeline. Firstly, the fast and complete valve closure is used to produce the gas-liquid two-phase transient flow in the gravity flow pipeline made of plexiglas. Secondly, by using the air fraction to modify the transient wave speed, two one-dimensional gas-liquid two-phase transient flow models, which take into account the influence of unsteady friction and pipe-wall viscoelasticity, are established based on the discrete vapor cavity model (DVCM) and discrete gas cavity model (DGCM). Experimental and model results show that DVCM can accurately simulate the experimental wave speed in the low pressure system when the initial flow regime is bubbly flow, while the average wave speed obtained by DGCM is larger than the experimental wave speed. In the simulation of transient bubbly flow, the results of DVCM are in good agreement with the experimental values, while the maximum peak values in the results of DGCM are larger than the experimental values, which demonstrates DGCM is more suitable for the design of pipeline safety. During the gas-liquid two-phase transient process, the compressibility of air makes the effect of pipe-wall viscoelasticity on pressure damping greatly weakened, which leads to the unignored effect of unsteady friction, and the pressure damping in the whole transient process becomes slow due to the presence of air.