Air expulsion from an end-of-pipe orifice in a rapidly filling horizontal pipe is investigated experimentally and analytically in order to more completely characterize the system's transient response. In particular, images of air-water patterns, air-volume variations, orifice flow regimes, and measured pressure histories are synchronized to elucidate the process of air expulsion. Air expulsion typically undergoes an early stage involving pressurization, expansion, and release of a portion of the initial air, events that generally occur even before the advancing water column reaches the pipe end. The next stage depends strongly on the orifice size. For a small discharge orifice, an oscillation of the residual air occurs with the discharge orifice being intermittently choked by water; by contrast, larger discharge orifices rapidly and completely expelled the air, often leading to high water-hammer pressures. Three distinct patterns of pressure oscillation are typically observed. With small orifices, the cushioning effect of the initial air tends to dominate, whereas slightly larger orifices lead to a more complex process of expulsion and more persistent and larger pressure oscillations. Even larger orifices often lead to severe water-hammer pressures. Thus, smaller orifices tend to result in smaller pressure fluctuations. As expected, both the initial-air volume and the inlet pressure significantly influence the transient response. A derived analytical model accurately...
COBISS.SI-ID: 14238211
Nowadays, plastic pipes play a key role in fluid conveyance, for example, in urban water supply systems. Dynamic analysis of designed water pipe networks requires the use of numerical methods that allow for solving basic equations that describe transient flows occurring in plastic pipes. In this paper, the main equations were formulated with pressure (p) and velocity (v) as the principal variables. A novel simplified retarded strain solution is used to properly model the pipe-wall viscoelasticity effect during transient flow process. Unsteady friction is calculated with the use of a filtered weighting function (with three exponential terms). The proposed numerical method enables the efficient modelling of transient flow in plastic pressurized pipes. Extensive simulations are performed and compared with experimental results known from three different European research centres (London, Cassino, and Lyon), with the aim of demonstrating the impacts of plastic pipe properties and frequency-dependent hydraulic resistance on transient pipe flow oscillations. The effectiveness of the proposed method for determining the creep functions of plastic pipes is also examined and discussed.
COBISS.SI-ID: 17045019