Experiment And Simulation On Hole-model Of Discharge Rate To The Gas-pipeline

Along with the natural gas utilization and pipeline scale expanding, as part of pipelines service for a long time and step into the aging phase, leakage accidents occur occasionally. Additionally, natural gas is inflammable and explosive, a great possibility of fire and explosion exists when leakage happens, then seriously threat the public security. Hence to carry out risk assessment of natural gas pipelines is especially important to the coordinated development of natural gas application and safety and health. Moreover, discharge rate calculation is a significant issue, also the prerequisite and foundation of consequence forecast and risk assessment.Currently, relatively mature models of discharge rate calculation include hole-model, pipe-model and hole-pipe generalized model. The derivation process of such models is mainly based on a series of conservation equations and assumed conditions, therefore, some defects are inevitable. For instance, the effect of hole-geometry feature to the discharge rate calculation is ignored, the discharge coefficient is arbitrarily chosen, results of discharge rate lack necessary verification, etc.The paper synthesizes quantities of study achievements, to further narrow the difference between ideal gas and real gas, the compressibility factor is expressed as a function of pressure and temperature and introduced into the derivation process of discharge rate models. Then, comparative analysis of applicability and precision among hole-model, pipe-model and hole-pipe generalized model is done. To research the effect of hole-geometry feature to the discharge rate, the gas-pipeline leaking simulation system is designed and constructed. At the same time, a full-scale CFD model of the leaking unit is established and its validity is proved through a quantitative evaluation combined with the experimental data. On this basis, the gas-pipeline leaking scene is reappeared and features of micro flow field including velocity vector distribution near the hole, velocity distribution of the hole-cross-section and mach-number distribution of center line are clear. Moreover, inherent law of choked flow of discharge rate and relationship between normal shock wave of supersonic speed flow and isentropic expansion near the hole are presented.Finally, results are used to the engineering application. To solve the question that discharge coefficient is arbitrarily chosen, a new method is presented in this paper. The influencing factors of discharge coefficient are determined, hole-geometry feature, pipe pressure and roughness included. Based on nonlinear fitting, the empirical formula of discharge coefficient and dimensionless ratio of pressure under different hole-shape and pipeline roughness is obtained. Combined with the hole-pipe generalized model, discharge rate is calculated quickly and accurately. The new method is promising to provide theoretical basis and scientific reference to the rigor and refinement of discharge rate calculation.