中文摘要：

为了模拟低流速情况下的流态转换和水击波的实际衰减过程,针对管流瞬时流速接近临界流速而导致的层流-紊流交替出现的情况,分别将层流摩阻损失公式和紊流摩阻损失公式引入到传统的特征线法瞬变计算模型,建立改进后的瞬变模拟复合数学模型.通过数值方法对伴随层-紊流交替情况下的水击全过程进行模拟得到关阀瞬变的压力波动时程,与传统瞬变模型计算结果相比,该波动过程线具有更快的衰减速度.结果分析表明,瞬变波的衰减过程实质是弹性波的能量衰减过程,摩阻损失是导致瞬变波衰减的直接原因,当流速较大时,能量消散以紊流摩阻为主,当流速较小时,能量消散以层流摩阻为主.对于瞬变波衰减的模拟,考虑层流区的实际摩阻损失后的衰减速度比传统水击模型计算的衰减速度快,因此,在瞬变波衰减的模拟中必须充分考虑层流摩阻的效应.

英文摘要：

An improved compound mathematical model was established to simulate attenuation of hydraulic transients with laminar-turbulent alternations, usually occured when pipeline flow velocity fluctuates near the critical velocity. Laminar friction resistance and turbulent friction resistance were considered respectively in this model by applying different resistance schemes to the characteristics method of fluid transient analysis. The hydraulic transients of valve clos- ing process were simulated using the model. More reasonable attenuation of hydraulic transients was obtained. Accurate attenuation is more distinct than that obtained from traditional models. The research shows that hydraulic transient is a type of energy waves, and its attenuation is caused by friction resistance. Laminar friction resistance is more important than turbulent friction resistance ff the flow velocity is smaller than the critical velocity. Otherwise turbulent friction resistance is more important. Laminar friction resistance is important in the attenuation of hydraulic transients for valve closing process. Therefore it is significant to consider different resistances separately in order to obtain more accurate attenuation of hydraulic transients.