The Research Of Fluid Transients In Low Pressure Hydraulic Pipeline

In the hydraulic transmission systems, after the valve is suddenly open and shut off, there will be a fluid transient in the form of pressure pulsation propagating along the pipeline. When the pressure transients occur in low pressure pipelines such as the suction lines of pumps or the return lines of a hydraulic system, gas bubbles and cavitation will occur inside the fluid. The growing and collapsing of gas bubbles and cavitation not only damage the flow continuity and reduce the working mediums physical performance, but also influence the propagation of pressure pulsation. Therefore, the study of the fluid transient accompanying the growing and collapsing of gas bubbles and cavitation in low pressure hydraulic pipelines is absolutely important for the prediction of the hydraulic pump performance and the safety of hydraulic system.In this paper, according to the Fluid Dynamic theory, mathematical model of the pressure transients accompanying the growing and collapsing of gas bubbles and cavitation in low pressure hydraulic pipelines is given, based on the continuity equation and motion equation. The mathematical models of friction item, the growing and collapsing of gas bubbles and cavitation are also introduced. The finite difference method and Matlab/Simulink are used to simulate the pressure transients accompanying the growing and collapsing of gas bubbles and cavitation in low pressure hydraulic pipelines. A method using selector block in Matlab Simulink to solve the equations in spatial dimension is developed. The pressure transients under different conditions such as different initial flow rate, different viscosity and different initial gas bubble volume are simulated. The experiments of the pressure transients accompanying the growing and collapsing of gas bubbles and cavitation in low pressure hydraulic pipelines are carried out. Two piezoelectric pressure transducers are used to measure the resulting pressure wave. And a high speed video camera is used to recode the growth and collapse of gas bubbles and cavitation behind the valve.