Calculation method of transient pressure of trapped air mass in pipe impinged by water flow

Abstract

The invention provides a method for calculate transient pressure of retained air mass in pipeline impinge by water flow. The equations of motion of water column and the instantaneous equations of gaspressure are established by taking the horizontal pressurized transmission / drainage pipeline with retained air mass as the center. The second-order nonlinear differential equations are obtained by simultaneous equations with the transient flow pressure of pipeline as the strain value and the instantaneous displacement of water column as the independent variable. The equation is subjected to linearization so as to obtain the calculation formula of air-water transient pressure of retained air mass in pipeline impinge by water flow, which takes into account the effects of time, local atmosphericpressure, gas state index, water flow density, inlet pressure, pipe length, and retained air mass length. The invention provides a tool for calculation of the peak value of air-water hammer pressure and oscillation period produced by the transient flow phenomenon that the water flow impinges on a retained air mass in a pressurized pipe, and provides theoretical basis for optimizing the engineeringdesign of the pressurized transmission / drainage pipeline, reducing the engineering cost and ensuring the safe operation of the engineering calculation.

Description

technical field [0001] The invention relates to the calculation of the water-gas transient flow process of a pressure transmission / drainage pipeline system, and belongs to the technical field of numerical calculation of air-water hammer pressure generated by a pressure transmission / drainage pipeline. Background technique [0002] In the pressurized water pipeline system, there is trapped air mass due to poor exhaust in some high-convex parts or closed ends of the pipeline. The gas-water hammer pressure generated by the variable flow phenomenon will be much greater than the general water hammer pressure, which is the main reason for the pipe burst. [0003] It has been one of the important subjects in the study of transient flow to solve the transient flow pressure generated by the water flow impacting the air mass in the water pipeline. At present, experimental research and numerical calculation models are mainly used for measurement and calculation analysis. [0004] Affe...

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Problems solved by technology

[0004] Affected by the incomplete similarity theory and similarity criterion of transient flow models, it is difficult to obtain reliable transient pressure values ​​of prototype pipelines through experimental research methods

In terms of numerical calculation methods, researchers ignore the elasticity of water and pipe walls and analyze according to rigid theory, and establish a one-dimensional rigid mathematical model; consider the elasticity of water body and pipeline, and establish a one-dimensional elastic water model, rigid plug, virtual plug, etc. Elastic mathematical models, but these equations themselves cannot directly obtain analytical solutions, only approximate solutions can be obtained by numerical integration, which involves complex graphic methods and programming, and it is difficult for engineers and technicians to use this method to calculate and predict pipeline internal transients. Transient pressure peaks that may be generated by variable flow and pressure variation with time

In addition, the study found that both rigid and elastic models have large deviations when the trapped air mass in the pipeline is small

Based on the above reasons, some researchers have also carried out the research on the approximate analytical solution of the maximum pressure of the water flow impacting the air mass, but the analytical solution expression of the maximum pressure generated by the impacting air mass and the oscillation period given by the researchers contains an unknown functional relationship, resulting in the air mass The maximum pressure and period cannot be directly calculated, and engineers and technicians cannot directly apply the formula to actual engineering

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