Study of transition process features in short gas pipelines by the method of characteristics
Abstract
The article's topic is the modeling of transient processes in gas pipelines using the approach of a short pipeline and solving the obtained equations by the method of characteristics. The research subject is the features of the dynamics of pressure, mass flow rate and gas velocity under discontinuous boundary conditions. The article deals with the problem of a temporary change in the inlet and outlet mass flow rate of gas in an elementary section with the known distribution of gas pressure and velocity at the beginning of the process. When modeling the process, the directional change in pressure from the local component of the gas inertia force and the supercompressibility of gas are taken into account. When solving the problem, the equations of conservation of momentum and mass are linearized by introducing the mass flow rate of gas; functions representing counter-propagating waves were introduced; the fulfillment of boundary conditions is ensured along with the characteristics. The calculation domain is partitioned into time bands with a step equal to the excitation travel time over the entire section's length. Each band is partitioned by its main diagonals into triangular subdomains. Formulas for calculating the pressure and mass flow rate of gas are obtained for the first time band. To obtain a solution to the problem for the remaining time bands, an algorithm was developed, where using the inlet sought-for values for the time band, their values at the end of this band were determined. Such an algorithm was applied both for the case of constant values of the functions participating in the boundary conditions and for their variable values. Depending on the difference between the inlet and outlet mass flow rates, solutions were obtained with periodic pressure changes and a widespread increase and decrease in pressure in the section with time. Three-link plots of the sought-for functions were constructed.