Abstract
In hydraulic systems, transient flow often occurs and may results in cavitation in pipelines. In this paper, the Computational Fluid Dynamics (CFD) method based on the Fluent software was used to investigate the cavitation flow in pipeline; the density-pressure model was incorporated into the continuity equation by using further development of UDF (user defined function), which reflects the variable wave speed of the transient cavitation flow, and the related algorithms were established based on weakly compressible fluid Reynolds Average Navier-Stokes (RANS) techniques. Firstly, the numerical simulations of the transient non-cavitation and cavitation flows caused by the fast closing valve in the reservoir-pipe-valve system were carried out by using the grid slip technique. The simulation results can enrich the flow field information such as velocity, pressure and vapor volume fraction. Through the evolution process of the pressure field, the propagation characteristics of pressure waves can be analyzed qualitatively and quantitatively. Through the evolution process of the velocity field, it can be seen that the velocity distribution in the wall area changes rapidly and has a high gradient, which mainly depends on the viscosity. However, the change of the velocity distribution in the core region is related to the velocity distribution of the history of the past time, which mainly depends on the diffusion. The formation, development and collapse of the cavity can be successfully captured, and it can be clearly and visually observed that the uneven distribution of vapor cavity in the direction of pipe length and pipe diameter, and the vapor cavity move slowly along the top of the pipe wall. Rarefaction wave’s propagation into pressure decreasing region and pressure increasing region can lead to different results of cavitation flow. The accuracy and reliability of the weakly compressible fluid RANS method were verified by comparing the calculated results with the experimental data.
Highlights
Hydraulic transients are caused by the rapid changes in pressurized pipelines and characterized by strong positive and negative pressures, which are often referred as water-hammer, and which probably cause device failures, system fatigues, leakages, or pipe ruptures, and can even be accompanied by cavitation when the liquid pressure in pipes drops below its corresponding vapor pressure, which may subsequently lead to more severe damages to the hydraulic system [1]
The transient cavitation flow phenomenon is replayed, and some of the simulation results are basically consistent with the experimental data, but they assume that the vapor cavity occupies the entire calculated section and the position remains the same, which is not the real condition, and they are impossible to reflect the essence of the cavity volume fraction transport
By considering the compressibility of water and introducing the fluid densitypressure equation that represented the pressure wave speed, a transient cavitation flow calculation model based on the weakly compressible fluid Reynolds Average Navier-Stokes (RANS) method was proposed
Summary
Hydraulic transients are caused by the rapid changes in pressurized pipelines and characterized by strong positive and negative pressures, which are often referred as water-hammer, and which probably cause device failures, system fatigues, leakages, or pipe ruptures, and can even be accompanied by cavitation when the liquid pressure in pipes drops below its corresponding vapor pressure, which may subsequently lead to more severe damages to the hydraulic system [1]. Such changes are normally triggered by valve opening/closing, pump startup/stop, load regulations of hydraulic turbine units, etc. As efficient techniques to get more information of hydraulic transients, the more accurate quasi two-dimensional (2D) unsteady friction model, which takes the velocity distribution of the cross-section into consideration attract more and more attention [6,7]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
