Liquid Pipeline Transient Flow Analysis And Its Application

Traditionally the calculation of friction terms in unsteady liquid pipe flow is based on the quasi-steady assumption that the unsteady friction in transients can be approximately calculated by the formulas in steady pipe flow. Almost all of the experimental and theoretical researches, however, are suggested that: (1)the steady flow and the transient flow have distinct friction characteristics and the unsteady friction in transients can be token as two parts, namely quasi-steady friction term and modified term; (2)the unsteady friction in transient liquid pipe flow would be underestimated by the traditional quasi-steady friction models which can not mimic the key physical processes in addition to predict the maximum and minimum pressure in water-hammer. As a result, there is significance in theory and practical engineering to study the unsteady friction in transients and propose more accurate unsteady friction models to simulate the transient pipe flow from one steady state to the next one. In this paper, it includes several parts as follows:Based on the conservation laws of mass and momentum equilibrium in transient liquid pipe flow, the basic equations are introduced in detail.On the basis of the quasi-steady assumption, the traditional quasi-steady friction model in liquid transients is proposed and its numerical solution with the method of characteristics is obtained. In addition, two sorts of the most promising unsteady friction models (i.e. Vardy&Brown unsteady friction model and Brunone unsteady friction model) which can be used to simulate liquid transients in turbulent, smooth pipe flow are proposed and their numerical solutions with the method of characteristics are obtained.The corresponding calculation program of the traditional quasi-steady friction model, Vardy&Brown unsteady friction model and Brunone unsteady friction model have been developed and applied to the transient simulation of the practical pipelines. After their corresponding simulation results being compared to the experimental measurement, the accuracy and preponderance of the two sorts of unsteady friction models in simulating transient events are testified.By means of numerical simulation with the traditional quasi-steady friction model and Vardy&Brown unsteady friction model, the quasi-steady and modified wall stress terms under different conditions are calculated. And the corresponding change laws and the influence of both of wall stress terms upon hydraulic transient in liquid transients are analyzed. And some of useful conclusions are drawn.The applicable fields of the above-mentioned three sorts of friction models are also discussed. And the conclusions gotten could be used to provide reference and instruct the suitable choice of different friction models in practical pipeline simulation in oil industry, such as raw oil pipeline and finished oil pipeline.