SPH Modeling of Transient Mixed Fluid Flows in Drainage Pipeline Systems

Mixed fluid flows (i.e., air and water) in drainage pipeline systems are common and harmful phenomenon, in which their complex interactions of different fluid components may cause serious drainage problems such as rapid filling, mixing and geysering in urban drainage pipeline systems under extreme storm events. Prediction and analysis of transient mixed fluid flows in the pipeline is of great importance to the design, construction and operation of such fluid piping systems in engineering practice for avoiding its harmfulness to the system and associates. Numerical modeling of transient mixed flow interface and propagation process has been a useful way to inspect and elaborate such complex interaction process, which however is still challenging due to the different properties and coupling techniques of open channel and pressurized flows. Currently, different numerical methods are available for the simulation of transient mixed flows in pipelines, including the classical methods such as the Method Of Characteristic (MOC), Finite Volume Method (FVM), Finite Difference Method (FDM), and Lattice Boltzmann Method (LBM). However, many previous applications in the literature have indicated that these classic methods could not be well applied to complex mixed flow process, especially with phase change, column separation, and flow discontinuity.

In recent year, the Smoothed particle hydrodynamics (SPH) has become a more and more popular numerical method because of its advanced features such as advection done perfectly, exact mass conservation, instinctive time independent, etc. As a result, this SPH based method has been developed to model some simple and common flows (e.g., steady and/or uniform flow) in open channels and pipelines in the literature. In this regard, it is expected to extend and develop further this advantageous method to more complex flow processes, such as transient mixed air-water flows studied in this paper. To this end, this paper aims to develop a suitable SPH method with specific innovations in the numerical scheme to solve the coupled two-equation model (Saint-Venant and water hammer /transient models), thereby tracking the transient open-channel-pressurized flow interface in closed conduits. The obtained numerical results are validated and verified by experimental data available in the literature as well as tested in the current work. The achievements and findings of this study are expected to provide alternative model and tool for the transient mixed flows in drainage pipeline systems.

Keywords: transient mixed flows; drainage pipe system; numerical simulation; Smoothed Particle Hydrodynamics (SPH)