管道倾角和壁面粗糙度对高速运动液体段塞脱落率影响的数值模拟研究

Numeral simulation on effects of inclination angle and wall roughness on mass shedding rate of high-speed liquid slug in pipelines

当对复杂地形条件下的输水管道系统进行维护时,流体会在低洼处汇集形成液体段塞。系统重启时,在上游驱动压力作用下,段塞将不断被加速。受到诸如管道倾角、壁面粗糙度等因素的影响,液体会从高速运动的段塞中脱落,导致段塞质量和长度发生变化。针对高压气体作用下管道内单个高速运动段塞的质量脱落问题,采用VOF两相流技术,通过三维CFD数值模拟试验,绘制了不同工况下液体段塞脱落长度与运动距离之间的关系曲线,研究了管道倾角以及壁面粗糙度对液体段塞脱落率的影响。结果表明:不同管道倾角下,液体段塞脱落率为一常数;随管壁粗糙度的增大,液体段塞脱落率以幂指数形式增大,直至逼近于某一常数。此外,从液体脱落的角度解释了段塞运动距离超过6倍段塞初始长度时,段塞会因全部液体脱落而发生破碎的现象。研究成果可为复杂地形条件下输水管道的系统设计提供理论指导。

When water conveyance piping systems under complex terrain conditions are maintained, liquids will collect at low-lying locations forming liquid slugs. When the system is restarted, the slug will be accelerated under the upstream driving pressure. Affected by factors such as pipe inclination angle and wall roughness, some liquid will shed from the high-speed slug, resulting in changes in slug mass and length. Aiming at understanding the mass shedding of single slug moving in pipeline driven by pressurized air, the relationship between liquid slug loss length and moving distance is studied by using three-dimensional CFD simulation, in which the VOF technique is applied to track the water-air interface. The influence of pipe inclination angle and wall roughness on the slug mass shedding rate is also investigated. The results show that the slug mass shedding rate is independent of pipe inclination angle, and it increases in power exponent form with the increase of pipe wall roughness until it approximates a constant. In addition, it is explained from the point of slug mass shedding rate that when the slug moving distance exceeds six times of the initial slug length, the slug will break up due to mass shedding. The results can provide theoretical guidance for the design of water conveyance pipeline system under complex terrain conditions.